Thalassas - Universidade de Vigo

Transcription

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Thalassas greek voice meaning...”of the sea”
Cover photograph: Photograph courtesy of Victoriano Urgorri
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Nº 27 (2) - 2011
Volume 27(2)
Thalassas
AN INTERNATIONAL JOURNAL OF MARINE SCIENCES
This volume includes selected papers
presented in the 3rd IWO
Referees of Special Volume 27(2) (3rd IWO 2010)
ALEXANDER MARTYNOV
ALEXANDRE LOBO DA CUNHA
ANNETTE KLUSSMANN-KOLB
BASTIAN BRENZINGER
CRISTIAN ALDEA VENEGAS
CYNTHIA TROWBRIDGE
EMILIO ROLÁN MOSQUERA
FRANCISCO JOSÉ GARCÍA GARCÍA
FREE ESPINOSA TORRE
GARY MCDONALD
GUILLERMO DÍAZ-AGRAS
HANS BERTSCH
HEIKE WAEGELE
INGO BURGHARDT
JESÚS SOUZA TRONCOSO
JUAN MOREIRA DA ROCHA
KATHARINA HÄNDELER
KATHE JENSEN
MICHAEL SCHROEDL
PATRICK KRUG
RICHARD S. WHITE, JR.
ROLAND ANTON
SCOTT JOHNSON
TIMEA NEUSSER
VICTORIANO URGORRI
Invited Editor
JESUS SOUZA TRONCOSO
University of Vigo
Scientific Committee
ALFREDO ARCHE MIRALLES
Instituto de Geología Económica.
C.S.I.C., Madrid (Spain)
TOMOHIRO KAWAGUCHI
Department of Environmental Health Sciences
The Norman J. Arnold School of Public Health
University of South Carolina (USA)
ANTONIO CENDRERO UCEDA
D.C.I.T.T.Y.M. Facultad de Ciencias
Universidad de Cantabria, Santander (Spain)
NORBERT P. PSUTY
Center for Coastal and Environmental Studies
University of New Jersey (U.S.A.)
DARÍO DÍAZ COSÍN
Departamento de Zoología
Facultad de Biología,
Universidad Complutense de Madrid (Spain)
RICARDO RIGUERA VEGA
Departamento de Química Orgánica
Universidade de Santiago de Compostela (Spain)
GRAHAM EVANS
Department of Geology. Imperial College
The London University (United Kingdom)
RAFAEL ROBLES PARIENTE
Instituto Español de Oceanografía
Madrid (Spain)
FERNANDO FRAGA RODRÍGUEZ
Instituto de Investigacións Mariñas
C.S.I.C., Vigo (Spain)
AGUSTÍN UDÍAS VALLINA
Departamento de Geofísica
Facultad de Física,
JOSÉ MARÍA GALLARDO ABUÍN
Instituto de Investigacións Mariñas. C.S.I.C., Vigo (Spain)
FEDERICO ISLA
Centro de Geología de Costas
Universidad de Mar del Plata (Argentina)
JESÚS IZCO SEVILLANO
Departamento de Bioloxía Vexetal
Facultade de Farmacia,
Universidade de Santiago de Compostela (Spain)
CARMINA VIRGILI RODÓN
Departamento de Estratigrafía
Facultad de Geología,
TAKESHI YASUMOTO
Department of Chemistry
Agricultural Faculty,
University of Tohoku (Japan)
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Cover Photograph:
“Specimen of Doto fragilis from Ría de Ferrol.”
Photograph courtesy of Victoriano Urgorri.
INDEX
9-21
Hans Bertsch & Cathy Moser Marlett
The seris, the sun and slugs: Cultural and natural history of Berthellina ilisima and other opisthobranchia in the
Central Sea of Cortez.
23-35
Juan Moreira, Antía Lourido, Eva Cacabelos & Jesús S. Troncoso
Patterns of spatial distribution of cephalaspideans (mollusca, gastropoda) in subtidal soft bottoms.
37-48
Cristian Aldea, Tamara Césped & Sebastián Rosenfeld
Opisthobranchs from Bernardo O’higgins National Park (S. Chile).
49-60
Abad M., Díaz-Agras G. & Urgorri V.
Anatomical description and biology of the splanchnotrophid Splanchnotrophus gracilis Hancock & Norman, 1863
found parasitizing the doridacean nudibranch Trapania tartanella Ihering, 1886 at the Ría de Ferrol (Galicia, NW
Iberian Peninsula).
61-75
Alexandre Lobo-da-cunha, Ana Rita Malheiro, Ângela Alves, Elsa Oliveira, Rita Coelho & Gonçalo Calado
Histological and ultrastructural characterisation of the stomach and intestine of the opisthobranch Bulla striata (heterobranchia:
cephalaspidea).
77-100
Urgorri, V., Díaz-agras, G., Besteiro, C. & Montoto, G.
Additions to the inventory of Mollusca opisthobranchia of Galicia (Nw Iberian Peninsula).
101-112
Schrödl M, Jörger KM, Klussmann-Kolb A & Wilson NG
Bye bye “Opisthobranchia”!
A review on the contribution of mesopsammic sea slugs to euthyneuran systematics.
113-119
Kohnert P, Neusser TP, Jörger KM & Schrödl M
Time for sex change! 3D-reconstruction of the copulatory system of the ’aphallic‘ Hedylopsis ballantinei (Gastropoda,
Acochlidia).
121-154
Katrin Göbbeler & Annette Klussmann-Kolb
Molecular phylogeny of the Euthyneura (Mollusca, Gastropoda) with special focus on Opisthobranchia as a
framework for reconstruction of evolution of diet.
155-168
Hans Bertsch
Nudibranch feeding biogeography: ecological network analysis of inter- and intra-provincial variations.
169-192
Kathe R. Jensen
Comparative morphology of the mantle cavity organs of shelled Sacoglossa, with a discussion of relationships with
other Heterobranchia.
193-224
Alexander V. Martynov
From “tree-thinking” to “cycle-thinking”: ontogenetic systematics of nudibranch molluscs.
225-238
Valérie Schmitt & Heike Wägele
Behavioral adaptations in relation to long-term retention of endosymbiotic chloroplasts in the sea slug Elysia timida
(Opisthobranchia, sacoglossa).
Thalassas, 27 (2): 9-21
An International Journal of Marine Sciences
THE SERIS, THE SUN AND SLUGS:
CULTURAL AND NATURAL HISTORY OF Berthellina Ilisina
AND OTHER OPISTHOBRANCHIA
IN THE CENTRAL SEA OF CORTEZ
HANS BERTSCH(1) & CATHY MOSER MARLETT(1)
Key words: Bulla gouldiana, Doriopsilla albopunctata, Cochimí, Bahía de los Ángeles
ABSTRACT
The Seris of northwest Sonora have a profound
cultural tradition of molluscan interaction, applying
common indigenous names to over 150 species of
molluscs. The Seris used the shelled cephalaspidean
Bulla gouldiana for pendant jewelry, and called
the animal cacaapxom (‘what fattens [something]’).
The common tropical eastern Pacific Nudipleura
opisthobranch Berthellina ilisima, although apparently
not used, was given the common name xepenozaah
(‘sun in the sea’).
(1) Instituto de Investigaciones Oceanológicas,
Universidad Autónoma de Baja California,
Ensenada, BC, México
[email protected]
During a 25-year study at Bahía de los Ángeles,
Baja California, Berthellina ilisima was the third most
common opisthobranch encountered. It exhibited
an annual life cycle, with reproductive activity
occurring from May to July. In contrast, the more
northerly common Californian species Doriopsilla
albopunctata had a seasonally earlier annual life
cycle, from July to June, with reproductive behavior
observed during January to April. Berthellina ilisima
feeds on Demospongiae poriferans.
THE SERIS
The Seris, or the Comcaac, as the people call
themselves, have lived for centuries along the eastern
coast of the central Sea of Cortez (Figure 1) and in
the desert and mountain regions of northwest Sonora,
Mexico (between approximately 28º-31º N; 111º-113º
W). Although there has been significant interchange
with neighboring Yaqui (south) and Piman (north and
east) peoples, as nomadic hunter-gatherers the Seris
are unique among the southwest North American
9
HANS BERTSCH & CATHY MOSER MARLETT
Figure 1: Map of the central Sea of Cortez. Cartography by Cathy Marlett.
original desert settlers. Their extensive use of marine
resources especially sets them apart. However,
these cultural behaviors were shared with the Baja
California peninsular and now-extinct Cochimí
peoples, with whom the Seris most likely had contact
in their forays across the Gulf of California on reed
balsas. Little is known of these travels aside from
sketchy accounts in Seri oral history.
The Seri origins remain unclear, and it is not
known how long they have inhabited the Gulf
region. Published archaeological evidence (based on
radiocarbon assays) is inaccurate. “Estimated dates
were never calibrated nor corrected for reservoir
effect. The only reliable date for the antiquity of
the Seris in their present location is Nicolás de
10
Cardona’s 1615 visit to Isla Tiburón. While he was
there others came over from the mainland” (Thomas
Bowen, pers. comm.). Linguistic analysis yields
fewer clues (see Hale & Harris, 1979: 173). Their
language is clearly not part of the Uto-Aztecan
family of the neighboring Pimas and Yaquis, and
a suggested Hokan relationship, including either
peninsular Yuman or California coastal Salinan, has
not been clearly established to date (Campbell, 1997;
S. Marlett, 2007 & 2008).
MOLLUSCS
Archaeological, linguistic and ethnographic
studies reveal a profound cultural nexus between the
Seris and molluscs. Large middens containing bivalve
CULTURAL AND NATURAL HISTORY OF Berthellina Ilisina AND OTHER OPISTHOBRANCHIA IN THE CENTRAL SEA OF CORTEZ
Figure 2: Midden shell deposits on the eastern shore of Isla Tiburón, 29 March 2009. Photo by Cathy Marlett.
and gastropod marine shell deposits of human origin
are common throughout the ancestral Seri territories
(Figures 2 and 3).
More than 150 mollusc species with over 250
molluscan Seri names are identified by the Seris, with
significant ethnographic information (C. Marlett,
work in preparation). Although today the primary use
is as food and stringing of shells for the tourist market
or personal adornment, in the past molluscs played
an important role in the Seri culture. Easily gathered
in the extensive intertidal area, molluscs figured
prominently in the Seri diet. Their shells were heavily
used as eating utensils, vessels and storage containers.
Shells were used to butcher meat, as scrapers and
digging tools, and to make pottery and shape clay
figures (Fig. 4). Others were used in such varied ways
as medicine or as pipes for smoking tobacco. Shells
were fashioned into toys or used in games. A child’s
doll uses the byssal fibers of the bivalve Pinna rugosa
as hair (Fig. 5).
OPISTHOBRANCHS
Because of their reduced or nonexistent shell,
opisthobranch molluscs have tended to be overlooked
or not used by indigenous cultures worldwide. This
is evidenced by the lack of common names in native
languages for these organisms. Along the Pacific coast
of the Americas, only three species of opisthobranchs
are known to have been given such a name by a prehistoric [pre-European] people. The scientific name
11
Figure 3:
A midden on the mainland shore of Sonora, bordering El Canal del Infiernillo, 17 February 2009. Photo by Cathy Marlett.
Figure 4:
The shell of a Simomactra dolabriformis clam being used to shape
clay figures. The Seri name for this bivalve is haxöl icaai,
‘clam shell for making pottery’. Photo by Cathy Marlett.
12
Figure 5:
Traditional Seri doll, made in the 1970s. It is somewhat unusual in
that it has hair made from the byssal fibers of Pinna rugosa.
Photo by Cathy Marlett.
Figure 6:
The first European drawing of the Seris, by Padre Adam Gilg,
S.J. (1692). From: Alegre, Burrus & Zubillaga, 1960: 144-145.
Original in the Central Jesuit Archives in Rome
(Archivum Romanum Societatis Jesu, Boh. 108)
Figure 7:
Shell of Bulla gouldiana. Drawings by Cathy Marlett.
for the nudibranch Tochuina tetraquetra (Pallas,
1788) is based on Tochni, its name among the people
of the Kuril Islands, who ate it raw or cooked (Bergh,
1879: 154, referencing Pallas’ original description).
We are aware that Doris amarilla Pöppig, 1829, was
described as a food item of the indigenous Chileans,
however no vernacular name is known to have
existed, and the species is regarded as a nomen nudum
(Schrödl, 1996).
se colocan una concha” (Montané Martí, 1996: 156).
Very possibly these shells are the bubble snail Bulla
gouldiana (Fig. 7). Ethnographic testimony supports
this interpretation, as a Seri woman recounted that
long ago the Seris would hang bulla shells from their
ears, where they would make a “pretty sound” as they
jangled together in the breeze. The Seri name for the
species is cacaapxom, ‘what fattens [something]’, a
name derived in Seri folklore.
We here report Seri names for two species:
Bulla gouldiana Pilsbry, 1895, and Berthellina ilisima
(Marcus & Marcus, 1967).
The Seris would have encountered the seasonally
abundant Bulla gouldiana during their searches of
sand flats at low tide or in beach drift.
The first European drawing of the Seris was made
by Padre Adam Gilg, S.J., in 1692 (Fig. 6). The lead
male depicted in the family procession is apparently
adorned with earrings. Although not obvious in the
drawing, Gilg specifically described the use of shell
earrings. He wrote that “En los lóbulos de las orejas
Berthellina ilisima is known by the recentlycoined common names orange blob (Behrens &
Hermosillo, 2005, and Kerstitch & Bertsch, 2007)
and babosa albaricoque or chabacano, the apricot
slug (Camacho-García, Gosliner & Valdés, 2005).
The Seris call this animal xepenozaah, ‘sun in
13
Figure 8:
Three individuals of Berthellina ilisima (48, 41 and 43 mm total
lengths), in situ underneath a rock, subtidal, 18 feet depth,
Punta la Gringa, BLA, 15 May 1992.
Photo by Hans Bertsch.
Figure 9:
Pair of Berthellina ilisima (35-40 mm in length), with egg mass,
in situ underneath a rock, subtidal, 10 feet depth,
Punta la Gringa, BLA, 27 February 1989.
the sea’, or ‘sol en el mar’. The conspicuous and
brilliant color of this common species (occurring
under rocks intertidally and subtidally) evokes the
fierce brightness of the Sonoran sun (Fig. 8).
disc-shaped shell shrivels uselessly on extraction.
Interestingly, when a Seri woman was shown a photo
of xepenozaah, she laughed and said that it reminded
her of preserved apricots, and made her hungry!
Xepenozaah was apparently not used by the
Seris; it was not eaten, and the delicate internal
There seems to be no religious nor mythical
significance attached to this slug nor to its solar
resemblance. The Seris’ traditional belief system that
included vision quests, shamanism, and placating
malevolent spirits (Bowen, 1983: 245), did not include
sun worship. So why did they have a common name
for such a non-used creature? It is a gorgeous and
curious marine animal, found frequently under rocks
in the central Sea of Cortez (Kerstitch & Bertsch,
2007). Such an obvious and oft-encountered beauty
demands a name.
Figure 10:
Copulating pair of Doriopsilla albopunctata (32 and 28 mm long)
with egg mass, in situ on top of rock, subtidal, ~12 feet depth,
Punta la Gringa, BLA, 26 June 1998.
14
In an anecdote from Seri oral history, long ago
a group of hungry Seris traded for food from a boat
passing through the Gulf. The boat carried food
that the Seris had never seen. There were sacks of
white things, which they referred to as potaat cmis
‘[things] like maggots’ (most likely rice), and other
things referred to as xepenozaah cmis ‘[things] like
a xepenozaah’. It is tempting to posit that these were
oranges, a non-native fruit.
Table 1:
Table
1. Totalofnumbers
the fiveopisthobranchs
most abundant
opisthobranchs
at Bahía
de los
Total numbers
specimensofofspecimens
the five mostofabundant
at Bahía
de los Ángeles,
1984-2010,
Ángeles, 1984-2010,
with numbers
and percentages
found
at three
different
collecting localities:
with numbers
and percentages
found at three
different
collecting
localities:
la Gringa, Cuevitas and the Islands
Punta la Gringa, Cuevitas andPunta
the Islands.
Total
P. la Gringa
Cuevitas
Islands
Elysia diomedea
2795
2519 (90.1%)
246 (8.9%)
30 (1.2%)
Doriopsilla gemela
1502
449 (29.9%)
1053 (70.1%)
Berthellina ilisima
617
428 (69.4%)
46 (7.5%)
143 (23.2%)
Doriopsilla albopunctata
513
424 (82.7%)
87 (17%)
2 (0.2%)
Aeolidiella chromosoma
426
389 (91.3%)
15 (3.5%)
22 (5.2%)
—
The Seri word for oranges is sahmees, a word with
unclear etymology. An interesting possibility is that
through time, a shortened version of the xepenozaah
cmis might have been zaah cmis, ‘what is like the
sun’, from which it is no great leap to arrive at the
word sahmees. One Seri family still pronounces the
name for orange as zahmees. Of course, there is the
possibility that oranges were first called zaah cmis,
and the slug’s name is not involved.
totaling 479.5 hours of search time. During each
scientific dive, all opisthobranch specimens found
were counted, identified and measured. Density of
specimens and species was measured by unit of search
time, the best method for comparing opisthobranch
densities between different sites (Nybakken, 1978). A
total of 95 opisthobranch species, distributed among
9820 specimens, was recorded (Bertsch, 2010a, and
pers. obser.)
NATURAL HISTORY: BERTHELLINA ILISIMA
AT BAHÍA DE LOS ÁNGELES
Of the five most common species encountered
(Table 1), Elysia diomedea (Bergh, 1894) and
Berthellina ilisima are common in the southern
Mexican and Panamic provinces (sensu Briggs, 1995),
but Doriopsilla gemela Gosliner, Schaefer & Miller,
1999, Doriopsilla albopunctata (Cooper, 1863) and
Aeolidiella chromosoma (Cockerell, in Cockerell &
Eliot, 1905) range northward to central and northern
California. They demonstrate both the temperate
and tropical provincial-level affinities of BLA
opisthobranchs (Bertsch, 2010b), a phenomenon first
reported by Steinbeck & Ricketts (1941: 227): “This
was a strange collecting place. The water was quite
cold, and many of the members of both the northern
and southern fauna occurred here.”
Bahía de los Ángeles (BLA), Baja California,
México, is in the central Sea of Cortez, due west of
the Seri ancestral lands. Evidence from radioactive
carbon dating indicates that members of the Comondú
Culture and their historical Cochimí descendants
have inhabited this region for almost 6,000 years
(Bowen, Ritter & Bendímez-Patterson, 2008), taking
advantage of the year-round water spring at the base
of the mountain enclosing the bay.
For over 25 years, the senior author has been
conducting a long term study (see Bertsch, 2008) of
the subtidal communities at BLA: two rocky shoreline
communities on the northwest side of the bay, at
Punta la Gringa and Cuevitas, and a third comprising
the islands and the southeastern outer side of BLA
(mapped in Bertsch, Miller & Grant, 1998). During
the period 1984-2010, 408 research dives were made,
Differences between the three BLA opisthobranch
communities (Bertsch, Miller & Grant, 1998; Bertsch
& Hermosillo, 2007) are shown by the occurrence
patterns of these five species. Over 80% of Elysia
diomedea, Doriopsilla albopunctata and Aeolidiella
15
Table 2a:
Average monthly lengths (in mm)
Table 2a. Average
monthly lengths (in mm)
of Berthellina ilisima,
of Berthellina Bahía
ilisima,
Bahía
de los Ángeles
de los
Ángeles
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
13.75
14.63
17.489
18.422
26.098
26.044
30.421
35.039
34.88
33.913
52.674
45.583
(N = 4)
(N = 27)
(N = 45)
(N = 116)
(N = 41)
(N = 68)
(N = 126)
(N = 51)
(N = 25)
(N = 23)
(N = 43)
(N = 12)
Table 2b:
monthly
lengthslengths
(in mm) (in mm)
Table 2b. Average
Average
monthly
of Doriopsilla
albopunctata,
of Doriopsilla
albopunctata,
Bahía de los Ángeles
Bahía de los Ángeles
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
10.667
8.0
12.0
12.615
18.846
33.563
35.986
44.578
42.356
48.759
40.708
35.421
(N = 3)
(N = 5)
(N = 11)
(N = 13)
(N = 26)
(N = 32)
(N = 71)
(N = 147)
(N = 87)
(N = 54)
(N = 24)
(N = 19)
chromosoma were found at Punta la Gringa. The
abundance of the other two species is spread between
two communities: 70% of Doriopsilla gemela
occurred at Cuevitas and 29.9% at Punta la Gringa,
whereas 82.7% of Berthellina ilisima occurred at
Punta la Gringa and 23.2% at the Islands (Table 1).
Berthellina ilisima (Fig. 9) was the third most
common species encountered. It is a subtropical
to tropical species, ranging throughout the Gulf of
California south to Ecuador, but has periodically been
reported from the more northerly warm temperate
waters of southern California, probably corresponding
to El Niño occurrences (Kerstitch & Bertsch, 2007).
In contrast, the fourth most abundant opisthobranch,
Doriopsilla albopunctata (Cooper, 1864), is more
northerly in distribution, ranging from Mendocino,
California, to Punta Eugenia, Baja California and in
the Sea of Cortez (Fig. 10).
Berthellina ilisima exhibited a distinct annual
cycle (Fig. 11) from August to July. Juveniles of the
new generation appeared in August (averaging 13.75
mm in length), reaching maximum average lengths
of 52.674 mm and 45.583 mm (Table 2a) in June and
July. Doriopsilla albopunctata also exhibited an
annual cycle, but it was staggered earlier seasonally
than B. ilisima, from July to June (Fig. 12). Average
monthly sizes ranged from 8 mm to 48.759 mm
(Table 2b).
Table 3:
Seasonal reproductive activity at Bahía de los Ángeles of Berthellina ilisima and Doriopsilla albopunctata
Table
3. Seasonal reproductive activity at Bahía de los Ángeles of Berthellina ilisima and
(records from 1984-2010). Numbers of egg masses and pairs engaged in copulatory behavior observed per month
Doriopsilla albopunctata (records
fromduring
1984-2010).
Numbers
of egg masses and pairs engaged
(none found
August through
December).
in copulatory behavior observed per month (none found during August through December).
Egg Masses
Berthellina Doriopsilla
January
February
March
April
May
June
July
16
—
4
—
1
2
7
2
1
9
7
1
1
1
—
Copulatory Behavior
Berthellina
Doriopsilla
—
—
—
—
1
9
—
6
14
11
5
1
1
—
Figure 11:
Annual life cycle of Berthellina ilisima, average lengths of individuals per month, BLA; data 1984-2010.
Regression line y = 8.146 + 3.22x; R = 0.953; significant at P = 0.007.
Both species also exhibited seasonally staggered
periods of reproductive activity (Fig. 13), a reflection
of their temperate or tropical water distributions.
Copulatory pairs of B. ilisima were found in May
and June, whereas most copulatory pairs of D.
albopunctata were seen from January to April (Table
3). Most egg masses of the “southern” Berthellina
ilisima were found mainly from May-July, whereas
egg masses of the “northern” Doriopsilla albopunctata
were primarily encountered in February-March.
At BLA the egg mass of Berthellina ilisima is
a small coiled, low yellow-orange ribbon (Fig. 9),
but Behrens & Hermosillo (2005: 40) illustrate a
curtain-like, high, fragile and white egg mass from
southern California specimens. These differences
require further study.
The genus Berthellina Gardiner, 1936
(Nudipleura: Pleurobranchomorpha) comprises six
species. All exhibit a similar orange (varying from
yellow to red) coloration pattern, and a primarily
circumtropical distribution (Fig. 14). Most species
of Berthellina are known to feed on sponges (Willan,
1984), although Scott Johnson reported that B.
delicata (erroneously cited as B. citrina) feeds on
the stony corals Tubastrea coccinea, Leptastrea
purpurea and Porites lobata in Hawaii (Bertsch
& Johnson, 1981; Willan, 1984), and Frederick M.
Bayer has reported the Caribbean B. quadridens to
feed on sea anemones in aquaria (Marcus & Marcus,
1967: 44).
Based on the analysis of fecal and stomach
contents from BLA specimens, it can be reported for
the first time that B. ilisima feeds on Demospongiae
of the genera Sigmadocia and Oscarella (pers. comm.
Jeffrey Goddard). In situ observations both in Sonora
(Fig. 15) and BLA (Fig. 16) also show this species
associated with sponges.
17
Figure 12:
Annual life cycle of Doriopsilla albopunctata, average lengths of individuals per month, BLA; data 1984-2010.
Regression line y = 4.709 + 3.679x; R = 0.881; significant at P = <0.001.
Figure 13:
Frequency of egg masses observed per month, BLA; data 1984-2010. Open circles, Berthellina ilisima; dots, Doriopsilla albopunctata.
18
Figure 14:
Distributional map of species of Berthellina. Numbers refer to the six known species. 1. Berthellina quadridens (Mörch, 1863); west Atlantic: Mexico
to Brazil, and Caribbean Islands, Haiti to Trinidad and Tobago. 2. Berthellina edwardsi (Vayssiere, 1896); east Atlantic: southern England to Las
Islas Canarias, and the Mediterranean coast of France and Spain. 3. Berthellina citrina (Rüppell & Leuckart, 1828); Red Sea endemic.
4. Berthellina delicata (Pease, 1861); west Indian Ocean to central Pacific Ocean, including Hawai’i. 5. Berthellina sp.; South Africa and
Madagascar. 6. Berthellina ilisima (Marcus & Marcus, 1967); eastern Pacific. Distributional data from Valdés et al., 2006: 108-109 (1);
Cervera, 2000 (2); Gosliner, Behrens & Valdés, 2008: 97 (3-5).
Figure 15:
Berthellina ilisima under intertidal rock, on sponge; north of
Desemboque de los Seris, Sonora, 11 March 2008.
Photo by Cathy Marlett.
ACKNOWLEDGMENTS
This work is a portion of two independent long
term studies by the authors, conducted on opposite
shores of the Sea of Cortez: “A Seri Ethnography
of Molluscs” (CM) and “The Natural History,
Composition and Variation of the Opisthobranch
Figure 16:
Berthellina ilisima on sponge, subtidal in situ, 18 feet depth,
Punta la Gringa, BLA, 15 May 1992.
Communities at Bahía de los Ángeles” (HB). Various
aspects of this article have been presented at meetings
of scientific societies: The Pacific Conchological Club
(Los Angeles, California, October 2009), San Diego
Shell Club (San Diego, California, October 2009),
XII Congreso de la Asociación de los Investigadores
del Mar de Cortés (Guaymas, Sonora, México,
19
March 2010), Joint Meetings 43rd Western Society
of Malacologists and 76th American Malacological
Society (San Diego, California, July 2010), Third
International Workshop on Opisthobranchia (Vigo,
Spain, September 2010), and XVI Congreso Nacional
de Oceanografía (Ensenada, Baja California, México,
November 2010). We are grateful for discussions with
our colleagues at these sessions that helped shape this
final version.
Dr. Jeffrey H.R. Goddard kindly allowed us to use
his information on the stomach and fecal contents of
Berthellina ilisima.
During our investigations numerous people have
generously helped us. We are grateful to the many
Seris who have shared their intimate knowledge of
their sea world, especially Manuel Monroy, who
pointed out the slug and provided its name, and
Evangelina López, who described the past use of the
bubble shell by the Seris. We thank Steve Marlett
for his help with linguistic details of the Seri data
presented here, and Thomas Bowen for comments on
archaeological dating of the Seri origins.
We thank our diving and research colleagues
at Bahía de los Ángeles, including Ricardo Arce
Navarro, Rosa del Carmen Campay, Brian Coleman,
Jeff Goddard, Alan Grant, Christopher L. Kitting,
Michael D. Miller, Antonio Reséndiz and Tom Smith.
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21
Thalassas, 27 (2): 23-35
PATTERNS OF SPATIAL DISTRIBUTION OF
CEPHALASPIDEANS (MOLLUSCA, GASTROPODA)
IN SUBTIDAL SOFT BOTTOMS
JUAN MOREIRA(1), ANTÍA LOURIDO(2,*), EVA CACABELOS(2,**) & JESÚS S. TRONCOSO(2)
Key words: Cephalaspidea; benthos; assemblages; sediment; Iberian Peninsula; Atlantic Ocean.
ABSTRACT
Cephalaspidean gastropods are common
components of shallow soft-bottom benthic
assemblages; they are, however, often overlooked in
numerous studies because of the small size of many
species. The diversity, composition and distribution
of cephalaspidean assemblages at three different bays
located in NW Iberian Peninsula are described from
quantitative data. In general, patterns of composition
of cephalaspidean faunas varied across locations;
in two out of three locations there were no patterns
of distribution that could be related to sedimentary
composition. Some species seemed to be present in
(1)Departamento de Biología (Zoología), Facultad de Ciencias,
Universidad Autónoma de Madrid, Cantoblanco,
E-28049 Madrid, Spain.
e-mail: [email protected]
(2)Departamento de Ecoloxía e Bioloxía Animal, Facultade de
Ciencias, Campus de Lagoas-Marcosende s/n, Universidade
de Vigo, E-36310 Vigo, Spain.
Actual address:
(*)Instituto Español de Oceanografía, Centro Oceanográfico de
A Coruña, E-15001 A Coruña, Spain.
(**)Laboratory of Coastal Biodiversity-CIIMAR, Rua dos Bragas
289, 4050-123 Porto, Portugal.
any given kind of sediment (coarser sandy sediments
or fine sand-mud); other species such as Retusa
truncatula showed, however, eclectic patterns of
distribution, which might be related to their life cycle
and other factors such as availability or preference
of prey.
INTRODUCTION
The Cephalaspidea constitutes a widespread and
diverse group of opisthobranchs (Wägele, 2004), which
are well represented in marine soft bottoms (Franz,
1970; Howard et al., 1994). In fact, many species
are provided with a cephalic shield, which helps the
animal to burrow in the sediment (Fretter & Graham,
1954). The taxonomic status and family composition
of the Cephalaspidea has been questioned in the last
years (see, for example, Haszprunar, 1985; Mikkelsen,
1996; Wägele, 2004; Wägele & Klussmann-Kolb,
2005; Malaquias et al., 2009a,b). Here, we retain the
term “Cephalaspidea” to refer to a number of families
traditionally considered within this taxa, such as
Acteonidae, Retusidae, Ringiculidae, Haminoeidae,
Philinidae and Cylichnidae, which are mostly found
on soft bottoms (García et al., 2008).
23
JUAN MOREIRA, ANTÍA LOURIDO, EVA CACABELOS & JESÚS S. TRONCOSO
Figure 1:
A. Location of the studied areas in Galicia (NW Iberian Peninsula). B-D. Location of sampling sites and distribution of sedimentary types
at the Ría de Aldán (B), Ensenada de Baiona (C) and Ensenada de San Simón (D).
24
PATTERNS OF SPATIAL DISTRIBUTION OF CEPHALASPIDEANS (MOLLUSCA, GASTROPODA)
Figure 2:
Total number of species (S) of cephalaspideans per sedimentary type at each location (A) and mean abundance (+SD) per site in each sedimentary
type at each location (B). GR, gravel; VCS-CS, very coarse/coarse sand; MS, medium sand; FS-VFS, fine/very fine sand; MU, mud. *,
one sampling site in total. Black bars, Aldán; grey bars, Baiona; white bars, San Simón.
Cephalaspideans may be common in soft bottoms
and seagrass beds (Sprung, 1994; Gosliner, 1995;
Rueda et al., 2009) but are easily overlooked if not
sampled with the appropriate methodology (Rueda et
al., 2009); this is mostly due to the small size of many
species (Collignon, 1960). Some cephalaspideans
are herbivores although carnivorous habits are more
widespread within the group; carnivore species
mostly feed on foraminiferans, polychaetes and
bivalves (Rasmussen, 1973; Berry, 1994a; Wägele
& Klussmann-Kolb, 2005; Malaquias et al., 2009a).
For instance, predation by philinids and retusids
may greatly influence the population dynamics of
their prey, such as snails and clams (Morton & Chiu,
1990; Barnes, 1999); some introduced species of
philinids might also represent a potential risk for
maintenance of populations of indigenous species
due to competition for trophic resources (Gosliner,
1995). On the other hand, several cephalaspideans
show seasonal and interannual fluctuations in
their presence and abundance as do other benthic
invertebrates (Seager, 1982; Berry, 1994b). In
addition, they may serve as potential bioindicators of
the quality of the benthic environment. For example,
Retusa obtusa (Montagu, 1803) has been shown to
resist high concentrations of organic matter, lipids
and heavy metals in polluted soft-bottom in harbours
(Guerra-García & García-Gómez, 2004).
The molluscan fauna of the Galician rías (eastern
Atlantic, NW Iberian Peninsula) is particularly rich,
both on hard and soft substrata (e.g. Rolán, 1983;
Rolán et al., 1989; Olabarria et al., 1998; Moreira
et al., 2005; Troncoso et al., 2005; Lourido et al.,
2006; Cacabelos et al., 2008). This is mostly due,
on the one hand, to the variety of intertidal and
subtidal habitats and, alternatively, to the particular
oceanographic regime of the rias, characterized by
upwellings between March-April and SeptemberOctober (Álvarez-Salgado et al., 2000); the latter
result in a high primary production and therefore in
an important food supply for benthic fauna (Blanton
et al., 1987; Figueiras et al., 2002). Despite their
ecological importance, few attention has been paid
to the distribution and diversity of cephalaspideans
in the Galician rías. Determining the patterns of
spatial distribution of benthic populations and their
relationship with sediment variables, including
those of taxa influencing the dynamics of other
species, is important to understand the processes
which determine the structure and evolution of
assemblages and for an adequate management of
the natural marine resources (Malaquias & Sprung,
2005). Therefore, in this paper we describe the
composition of the cephalaspidean faunas in a range
of shallow-water sediments at several locations within
the Galician rías, and test whether there are any
25
Figure 3:
Total abundance per sedimentary site (%; bars) and mean abundance per site (indiv. 0.28m2 + SD; line) of cephalaspidean species (>20 indiv.) at
the Ría de Aldán (AL). GR, gravel; VCS-CS, very coarse/coarse sand; MS, medium sand; FS-VFS, fine/very fine sand;
MU, mud. *, one sampling site in total.
relationship among patterns of distribution and those
of granulometric composition.
oriented towards West and therefore exposed to the
influence of winter storms.
MATERIALS AND METHODS
Sampling was done in December 1995 (Baiona),
July 1997 (Aldán) and November 1999 (San Simón).
Geographic coordinates and abiotic features of
sampling sites may be found in Moreira et al. (2005;
Baiona), Lourido et al. (2006; Aldán) and Cacabelos
et al. (2008; San Simón). Sites were located at depths
of between 2-12 m (Baiona), 3-42 m (Aldán) and 2-28
m (San Simón). Sediments ranged from gravel to
mud in Baiona and from very coarse sand to mud in
Aldán and San Simón, with a predominance of sandy
sediments at the first two locations and that of muddy
sediments at the latter.
Studied areas
The three studied locations correspond to inlets
or small embayments at the mouth of the Ría de Vigo
(Ensenada de Baiona; 42º07’N-42º09’N, 08º49’W08º51’W) and the Ría de Pontevedra (Ría de Aldán;
42º16’N-42º20’N, 08º49’W-08º52’W), and an inlet
in the innermost part of the Ría de Vigo (Ensenada
de San Simón; 42º17’N-42º21’N, 8º37’W-8º39’W)
(Figure 1). The mouth of the three locations is
26
Sampling
The same sampling methodology was used at the
three locations. Five replicate samples were taken at
each site by using a quantitative Van Veen grab with
a sampling area of 0.056 m 2; a total area of 0.28 m 2
was therefore sampled at each site. Samples were
sieved through a 0.5 mm mesh and fixed in 10%
buffered formalin for later sorting and identification
of the cephalaspideans. Empty shells were neither
identified nor counted. An additional sediment
sample was also taken at each site to determine
the granulometric composition, grain-size median
(Q50), sorting coefficient (So), calcium carbonate
content (%) and total organic matter content (%). The
following sedimentary fractions were considered:
gravel (>2 mm), very coarse sand (2-1 mm), coarse
sand (1-0.5 mm), medium sand (0.5-0.25 mm), fine
sand (0.25-0.125 mm), very fine sand (0.125-0.063
mm) and silt/clay (<0.063 mm). Calcium carbonate
content was estimated by sample treatment with
hydrochloric acid; total organic matter content was
estimated from the weight loss on combustion at
450ºC for 4 hours.
(centroids) were classified by cluster analysis based
on the group-average sorting algorithm. Clusters of
sites determined as statistically significant by profile
test SIMPROF (P<0.05) were considered as having
a similar fauna (Clarke et al., 2008). Non-metric
multidimensional scaling (nMDS) was used to produce
the ordination of centroids; values of selected abiotic
features were further superimposed to detect visually
any related pattern in that ordination. Multivariate
analyses were done through the PRIMER 6 software
package (Clarke & Gorley, 2006).
The possible relationship between the
cephalaspidean fauna and abiotic variables
(granulometric fractions, grain-size median, sorting
coefficient, organic matter, calcium carbonate,
depth) at each location was explored using the BIOENV procedure (PRIMER). All variables expressed
in percentages were previously transformed by log
(x+1) and then normalised prior to the analysis.
Furthermore, correlations among abiotic variables
and the abundance of the numerically dominant
species (>20 individuals in total in any given
location) were determined through the Spearman’s
coefficient.
Data analyses
RESULTS
Total abundance (N) and total number of species
(S) were determined to assess the structure of the
cephalaspidean assemblage; those biotic parameters
were either calculated for each sampling site, a group
of sites corresponding to any given sedimentary type
or any given location.
The Bray-Curtis similarity index was used to
determine affinities in faunal composition among
sites (Bray & Curtis, 1957); therefore, a similarities
matrix was constructed based on species abundance,
which were previously transformed by applying
the square-root transformation to downweight the
contribution of the most abundant species. Data were
previously averaged across the five replicates for each
site thus obtaining a centroid (Bulleri & Chapman,
2004). From the similarities matrix, sampling sites
A total of 639 individuals representing 11 species
were found in the three studied locations (Table
1). The Ensenada de Baiona was richer in terms of
species diversity (S: 8) and mean abundance per site
(indiv. per m 2; mean ± SD: 15.8 ± 22.4), followed
by the Ría de Aldán and Ensenada de San Simón
(S: 6 and 3, mean ± SD: 7.3 ± 14.2 and 3.9 ± 9.1,
respectively). Retusidae was the most diverse family
(4 species) representing 70% of total abundance,
followed by Philinidae (3 spp., 12% abundance).
Retusa truncatula (Bruguière, 1792) and Cylichna
cylindracea (Pennant, 1777) were present at the three
locations. Philine spp. and Cylichnina umbilicata
(Montagu, 1803) were only found at Baiona while
Retusa mammillata (Philippi, 1836) and Ringicula
auriculata (Ménard de la Groye, 1811) were exclusive
27
Figure 4:
Total abundance per sedimentary site (%; bars) and mean abundance per site (indiv. 0.28m2 + SD; line) of cephalaspidean species (>20 indiv.)
at the Ensenada de San Simón (SA) and the Ensenada de Baiona (BA). GR, gravel; VCS-CS, very coarse/coarse sand; MS, medium sand; FS-VFS,
fine/very fine sand; MU, mud. *, one sampling site in total.
28
of Aldán. Retusa truncatula was the most abundant
species at Aldán and San Simón while C. umbilicata
contributed to more than half of the total abundance
at Baiona.
At the Ría de Aldán, cephalaspideans were found
at most of sampling sites (24 out of 27; 89%) and
at the Ensenada de Baiona were present in 15 out
of 21 sites sampled (71%); no specimen was found
at gravelly sediments in the latter. On the contrary,
cephalaspideans were more scarcely present at the
Ensenada de San Simón, being found in 12 out of
29 sites (41%), and were absent in most of the sites
corresponding to shallower muddy sediments.
Species diversity was greater in fine-very fine
sand sites at Baiona (S: 6) than in other sediments
(Figure 2A); the lowest number of species was found
in coarse sand at Baiona and medium sand at San
Simón (one species each). In coarse sandy sediments,
cephalaspideans were more abundant at San Simón
while in finer sandy sediments and mud those had
a greater abundance at Baiona than at the other two
locations (Figure 2B).
Three species (Retusa mammillata, Cylichnina
umbilicata, R. auriculata) appeared to show specific
patterns of distribution according to sediment
composition in some locations. Thus, the former
was found at Aldán in coarser sediments (gravel
to medium sand) at the deepest sites, reaching the
greatest mean abundance per site in very coarsecoarse sand (Figure 3A); Cylichnina umbilicata was
found at Baiona in medium and fine sand and showed
its greater mean abundance in the former (Figure
4C). Ringicula auriculata was present at Aldán
in medium sand to mud, showing an increasing
mean abundance per site following a decrease in
grain-size median (Figure 3C). Retusa truncatula
showed different patterns of distribution according
to the location and was present in a wide range of
sediments. At Aldán, this species showed its greatest
abundance at medium sand and was also found in
other sandy sediments, gravel and mud (Figure 3B);
at San Simón, R. truncatula was mostly found both in
coarse sand and muddy bottoms (Figure 4A) although
abundance varied greatly among sites. At Baiona,
R. truncatula was mostly present in finer sediments
(from fine sand to mud), being more abundant in
mud (Figure 4B). Cylichna cylindracea was present
at the three locations and showed different patterns
of distribution. At Aldán, it was present in a range of
sediments but was more abundant at fine sand (Figure
3D); at Baiona, the distribution of this species was
restricted to fine-very fine sand (Figure 4D) while at
San Simón the few specimens found were present in
mud. Philinids were only found at Baiona in coarse to
medium sand (Figure 4E-F); the three species found
were only represented by juvenile specimens.
Cluster analysis and SIMPROF test detected
significant groups of sites for Aldán and San Simón
but not for Baiona. The graphic representation
of the nMDS for Baiona showed that sites with
coarser granulometry plotted separately from those
of fine sand and mud (Figure 5C-D). Groups of
sites determined for Aldán and San Simón were
composed by sites which differ in their granulometric
composition, in some cases ranging from gravel
to mud (cf. Figures 5A, E); mean similarity within
groups of sites was between 20-45%.
At Aldán and San Simón, the BIO-ENV procedure
showed low correlations among abundance data
and any combination of the measured sedimentary
variables (ρw<0.45); correlations were higher for
Baiona (ρw>0.60). The best correlations were
obtained for the combination of coarse sand, grainsize median, sorting coefficient and depth (ρw:
0.62; Baiona), depth and sorting coefficient (ρw:
0.45; San Simón) and calcium carbonate (ρw: 0.17;
Aldán). The graphic representation of the nMDS
ordination showed that, for Baiona, sites tended
to be plotted according to a gradient in grain-size
median (Figure 5D); patterns for Aldán and San
Simón were less defined (Figure 5B,F only shows
nMDS ordinations with values of calcium carbonate
and depth superimposed) which reflected the low
29
Figure 5:
nMDS ordination of sampling sites based on the Bray-Curtis similarity index applied to abundance data (centroids) including superimposed values
of selected environmental variables (circles). A-B, Ría de Aldán (B, calcium carbonate); C-D, Ensenada de Baiona (D, grain-size median); E-F,
Ensenada de San Simón (F, depth). Groups of sites determined by the SIMPROF test are shown with dotted line.
30
correlations obtained. On the contrary, correlations
obtained through the Spearman’s coefficient among
any given variable and abundance of some of the more
abundant species showed more definite patterns,
which may explain the variation of abundance
and presence across sediments (see Figures 3-4).
At Aldán, the abundance of Retusa mammillata
showed a significant positive correlation with gravel,
grain-size median (P<0.01) and calcium carbonate
(P<0.05), and Cylichna cylindracea with fine sand
(P<0.05). At Baiona, Cylichnina umbilicata showed
positive correlations with medium sand (P<0.01) and
calcium carbonate (P<0.05) and Philine punctata with
medium sand (P<0.05); Philine aperta showed a high
positive correlation with very coarse and coarse sand
(P<0.001). At San Simón, R. truncatula was positively
correlated with coarse sand (P<0.01) and negatively
with organic matter (P<0.05).
DISCUSSION
Diversity and composition of cephalaspidean
assemblages showed differences among the three
studied locations. Species diversity was greater at
Aldán and Baiona, which have a variety of sandy
sediments, than at San Simón, where soft bottoms
are mostly muddy. In general, the Galician rías that
have a greater sedimentary heterogeneity show, in
turn, a greater benthic diversity (Garmendia et al.,
1998; Troncoso et al., 2005; Moreira et al., 2009). This
has been related to the presence of a wider variety
of habitats (i.e. different kind of sediments) and
microhabitats within sediments (e.g. more interstitial
spaces available in coarser sandy sediments than
in muddy ones; Pearson & Rosenberg, 1978). In
addition, cephalaspideans were found in a greater
proportion of sampled sites at Aldán and Baiona
than at San Simón. This fact might be due to the
greater variations in salinity occurring in the latter,
which influence large intertidal and shallow-water
areas, resulting from freshwater inputs of several
rivers (Vilas et al., 1995). Those salinity fluctuations
are known to constitute a severe limitation for the
survival of many benthic species (Planas & Mora,
1987). However, previous work showed that most of
the species found here could tolerate wide variations
of many physico-chemical factors, including salinity,
at least in Mediterranean lagoons (Cattaneo Vietti &
Chemello, 1991). Other possible explanation may be
attributed to the negative effects on the biota of the
anthropogenic perturbations occurring in San Simón,
mostly due to sewage disposal and mussel culture on
rafts taking place in several parts of the inlet. This
results in an increase of organic matter content and
derived phenomena of anoxia in the sediment, which
represent adverse conditions for the survival of many
taxa (Gray, 1979).
There were differences in the presence of some taxa
among locations and sedimentary types. For example,
philinids and Cylichnina umbilicata were absent from
sandy sediments at Aldán but present in coarse and/
or medium-fine sand at Baiona; the opposite pattern
was found for Retusa mammillata, mostly present in
coarser sandy sediments at Aldán. Because coarse
and medium sand sediments are present in large areas
of the outer-middle part of both inlets, it is difficult
to explain why not all those species were present in
both locations. This fact might reflect differences
in environmental conditions related to the time of
the year of sampling and the life cycle of species.
In temperate latitudes, abundance and presence of
some cephalaspideans may vary through the year
because of a number of abiotic factors (e.g. Berry,
1994b); wind have, for instance, a great influence
in recruitment, mostly during winter-spring, when
dispersal of benthic eggs occurs and those are more
vulnerable to unfavourable conditions (Berry, 1994b).
In fact, differences in abundance of several degrees
of magnitude are known to occur for the same season
among different years (Berry, 1994b), which may
reflect whether there was successful recruitment or
not. On the other hand, some cephalaspideans have
a one-year life cycle (Rasmussen, 1973) and adults
die after spawning around mid or late spring (Berry,
1989; Malaquias & Sprung, 2005) which makes it
difficult to find them in samples from early summer.
For example, philinids were only found at Baiona and
31
Table 1:
List of Cephalaspidea species found at the three studied locations, showing their total abundance (ABU; %) and presence (PRE, number of sites in
which any given species is present referred to the total sampled in each location; %). Range of depth (DEP; m) and sedimentary types (SED) where
each species was found is also shown. GR, gravel; VCS, very coarse sand; CS, coarse sand; MS, medium sand;
FS, fine sand; VFS, very fine sand; MU, mud.
Aldán
Species
Baiona
San Simón
ABU
PRE
DEP
SED
ABU
PRE
DEP
SED
ABU
PRE
DEP
SED
-
-
-
-
0.3
4.8
11
VFS
-
-
-
-
21.7
22.2
17-36
GR, VCS, CS,
-
-
-
-
-
-
-
-
16.0
38.1
2-11
FS, VFS, MU
79.1
31.0
2-4
VCS, CS, MS,
Family Acteonidae
Acteon tornatilis (Linné, 1758)
Family Retusidae
Retusa mammillata (Philippi, 1836)
MS
Retusa truncatula (Bruguière, 1792)
38.4
37.0
3-42
GR, VCS, MS,
FS, MU
Cylichnina umbilicata (Montagu, 1803)
Volvulella acuminata (Bruguière,
FS, MU
-
-
-
-
55.3
33.3
7-11
MS, FS, VFS
-
-
-
-
1.0
3.8
13
FS
1.8
9.5
3-8
FS, MU
-
-
-
-
16.2
22.2
4-18
MS, FS, MU
-
-
-
-
-
-
-
-
2.5
3.7
4
MS
-
-
-
-
10.9
17.2
2-4
VCS, CS, FS,
1792)
Family Ringiculidae
Ringicula auriculata (Ménard de la
Groye, 1811)
Family Haminoeidae
Haminoea navicula (da Costa, 1778)
MU
Family Philinidae
Philine aperta (Linné, 1767)
-
-
-
-
6.6
23.8
8-12
CS, MS
-
-
-
Philine punctata (Adams, 1800)
-
-
-
-
10.0
14.3
8-10
MS, FS
-
-
-
-
Philine scabra (Müller, 1784)
-
-
-
-
3.6
9.5
8-9
MS
-
-
-
-
20.2
44.4
4-33
CS, MS, FS,
6.3
19.0
7-11
FS, VFS
10.0
10.3
4-10
MU
Family Cylichnidae
Cylichna cylindracea (Pennant, 1777)
MU
those were just represented by juvenile specimens.
Therefore, differences in environmental conditions
among sampling periods might partially explain the
different patterns of distribution and presence among
the studied areas.
The retusid Retusa truncatula was present in
the three studied locations and appeared in a variety
of substrata, ranging from gravel to mud, as shown
by previous work (e.g. Rasmussen, 1973; Urgorri &
Besteiro, 1983; Hoisaeter, 2009), although abundance
varied among sediments within locations. One possible
explanatory model for this pattern of distribution
could be that variation in abundance across sediments
might not reflect preferences in granulometry but
seasonal and spatial variations in the presence and
quantity of prey. For example, predatory habits of R.
truncatula switch between foraminiferans and small
32
prosobranchs (juvenile Bittium and Hydrobia) along
the year (Rasmussen, 1973). Similar feeding patterns
have also been reported for R. obtusa, which major
prey item during reproduction is the snail Hydrobia
ulvae (Pennant, 1777), instead of foraminiferans
(Berry et al., 1992; Berry, 1994a). In addition, it
is known that some cephalaspideans may prey on
different species in different areas or when migrating
to deeper areas (Taylor, 1982; Morton & Chiu, 1990;
Gosliner, 1995). Therefore, it is likely that widespread
species may be present in a large variety of sediments
being their abundance dependant on the presence of
prey, rather than on some hypothetical preference for
any given kind of sediment. Thus, at the three studied
locations, the largest abundances of R. truncatula
were found where their potential prey was abundant,
whether the sediment was sandy or muddy. At Baiona,
this happened in a muddy site where the snail Bittium
reticulatum (da Costa, 1778) reached densities of 600
indiv. m-2; Moreira et al., 2005); at Aldán, the largest
abundances of R. truncatula and B. reticulatum
(Lourido et al., 2006; 160 indiv. m-2) were found at
a medium sand site. Finally, at San Simón, most of
the specimens of this retusid were found in three
muddy sites where H. ulvae was the numerically
dominant species of the molluscan assemblage
(Cacabelos et al., 2008). Anyway, explaining the
observed patterns would require carefully planned
manipulative experiments, to test whether there is
or not sedimentary preferences and the role of the
presence of prey across different kinds of sediment
(Berry & Thomson, 1990; Olabarria et al., 2002).
ACKNOWLEDGEMENTS
The authors are grateful to F.J. Cristobo, C.
Olabarria, P. Reboreda and members of the Adaptaciones
de Animales Marinos laboratory (Univ. Vigo) for their
help during field work. A.L. was supported by a FPU
scholarship of the Spanish Ministry of Education and
Science Ministry. Two anonymous referees provided
constructive comments that helped to improve the final
version of the manuscript.
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Thalassas, 27 (2): 37-48
OPISTHOBRANCHS FROM BERNARDO
O’HIGGINS NATIONAL PARK (S. CHILE)
CRISTIAN ALDEA(1), TAMARA CÉSPED(1) & SEBASTIÁN ROSENFELD(2)
Key words: Mollusca, Gastropoda, Opisthobranchia, Magellan Region, fjords, taxonomy, distribution, biogeography.
ABSTRACT
The Magellan Region, ranging from Northern
Patagonia Icefield (45ºS) to Cape Horn (56ºS), is
formed by a complex net of fjords and channels
created by glacial and post-glacial processes. The
knowledge on the group Opisthobranchia (Mollusca:
Gastropoda) generated in the Magellan Region began
at the end of the 19th century and it continued toward
the first half of the 20th century. After a long ceasing
period, the studies were intensified during the last
years. Nevertheless, there are several and extensive
areas of channels and fjords on which opisthobranchs
have not been reported. A project of territorial
characterization of the Bernardo O’Higgins National
Park, an extensive protected area (35,000 km 2) that
is located in the heart of fjords and channels zone,
it allowed to carry out a baseline study of marine
(1) Fundación Centro de Estudios del Cuaternario de FuegoPatagonia y Antártica (CEQUA); Universidad de Magallanes;
Av. Bulnes 01890, Casilla 737, Punta Arenas, Chile. E-mail:
[email protected].
(2) Departamento de Ciencias y Recursos Naturales, Facultad
de Ciencias, Universidad de Magallanes, Avenida Bulnes
01855, Casilla 113-D, Punta Arenas, Chile. E-mail: srosenfe@
umag.cl.
ecosystems of shallow bottoms adjacent to the park.
The objective of this work is to get to know the species
of opisthobranchs (sensu lato) found in the survey,
pointing out findings about taxonomy, distribution
and biogeography. Twenty-three sites were sampled
by means of SCUBA diving at 5–15 m depth.
The obtained animals were sieved, fixed, sorted,
preserved in alcohol 70%, identified, measured and
photographed. Forty-three individuals belonging to
eight different species were registered; all of them
new records for the park. These correspond to 15% of
total species of gastropods recorded in the study. The
family Discodorididae was the best represented with
two species: Diaulula variolata (d’Orbigny, 1837)
and D. punctuolata (d’Orbigny, 1834); other families
were represented by one species each: Acteonidae,
Diaphanidae, Chromodorididae, Flabellinidae,
Onchidorididae and Tritoniidae. The records of
Toledonia perplexa and D. variolata suppose an
extension of their known distributions. Although
this report represents a progress in knowledge of
the marine fauna of the park, the species scarcely
represent 14% of opisthobranchs known in the
latitudinal band 45–55ºS. Therefore, more intensive
studies are necessary to improve the malacologic
knowledge of the area.
37
CRISTIAN ALDEA, TAMARA CÉSPED & SEBASTIÁN ROSENFELD
Figure 1:
Geographic situation of Bernardo O’Higgins National Park and location of sampling sites (PNBO).
38
OPISTHOBRANCHS FROM BERNARDO O’HIGGINS NATIONAL PARK (S. CHILE)
INTRODUCTION
The Magellan Region, referred as the Patagonian
shelf located at the southern tip of South America,
ranging from 45ºS (Northern Patagonia Icefield)
to 56ºS (Cape Horn Archipelago) is formed by a
complex net of fjords, channels and internal seas
created by glacial and post-glacial processes for
about 85–90% of the last 800,000 years (McCulloch
et al., 1997). This resulted in a geomorphologic
area with roughly 32,000 km of shoreline (Guzmán,
1992), which, in the early times of surveys, got
to have great importance from a biological and
ecological point of view.
Great part of the knowledge on the molluscs
generated in the Magellan Region began to be
gestated at the end of the 19 th century and it
continued actively at beginning and first half of the
20 th century. Dell (1971), starting from the “Royal
Society Expedition to Southern Chile, 1958–1959”,
carried out an exhaustive recapitulation of the
investigations and reports generated previously.
Years later, Reid and Osorio (2000) elaborated
a detailed study on the molluscs of the north
area of the Magellan Region, contributing valuable
taxonomical and ecological information. Almost, in
the same period, several reports generated starting
from the research cruises “Victor-Hensen” (e.g.
Linse, 1997, 2002) and “CIMAR-FIORDOS” (Osorio
and Reid, 2004; Osorio et al., 2005, 2006; Cárdenas
et al., 2008) were published.
The group Opisthobranchia presented, however,
a parallel development of researches in the region
and the subsequent generation of knowledge.
From the firsts expeditions focused on the area
and subsequent detailed studies carried out (see,
for example, Bergh, 1884; Eliot, 1907; Odhner,
1926; Marcus, 1959), many years lapsed so that the
knowledge of the group was intensified. In this way,
three extensive works providing new information on
a couple of species were published: “Nudibranchia
and Sacoglossa of Chile” (Schrödl, 1996a), “Sea slug
of Southern South America” (Schrödl, 2003) and
“Opisthobranchs from the Chilean coast” (Fischer,
2006). The former consisted basically on a study
of the external morphology and distribution of 42
species of the Chilean and southern Argentinean
coasts. The second is a systematic, biogeographical
and biological study of 65 species of the same area,
where also an exhaustive summary of previous
investigations is provided. The last work essentially
gathers taxonomic, morphological and histological
studies of several nudibranch species stemming
from a thesis research. At the same time, those
researchers together with other collaborators
developed numerous detailed studies of several
groups and some studies of the distribution and
zoogeography (e.g. Fischer and Ortea, 1996; Schrödl,
1997a, 1997b; Fischer et al., 1997; Schrödl, 1999a,
1999b; Schrödl and Millen, 2001; Schrödl and
Wägele, 2001; Fischer and Cervera, 2005; Schrödl et
al., 2005). On the other hand, other authors studied
groups mainly of the Magellanic and Patagonic
coasts (e.g. Muniaín and Ortea, 1997; Valdés and
Muniaín, 2002; Muniaín et al., 2007).
However, there is a lack of knowledge from
several areas of the channels and fjords. Besides
the abovementioned specific studies, there are
few recent reports of molluscs including some
opisthobranch species (e.g. Reid and Osorio,
2000; Osorio and Reid, 2004). The project of
territorial characterization of Bernardo O’Higgins
National Park, which is placed in the Chilean fjord
and channels zone, allowed developing a survey
carrying out a baseline study of marine ecosystems
and diversity of shallow bottoms adjacent to the
park. A prior exhaustive check to the work that
reported molluscs from the surrounding area to
the park (e.g. Dell, 1971), allowed to recognize 64
species of benthic molluscs (29 gastropods), among
which there were no records of opisthobranchs.
The objective of this work is to get to know the
species of opisthobranchs found in the survey,
detailing taxonomical findings and its areas of
biogeographical distribution.
39
Figure 2:
Pie chart showing the number of species (n) and percentages of free-living benthic marine non-colonial invertebrates from the
Bernardo O’Higgins National Park.
MATERIAL AND METHODS
Bernardo O’Higgins National Park is placed
in the Chilean geopolitical regions of Aysén and
Magallanes, between 48.0–51.6ºS and 73.3–75.8ºW
(Fig. 1). With more than 35,000 km 2, it is the largest
national park in the country and one of the most
extensive in the world. Its coastal line is developed
basically by way of countless channels and fjords
along more than 400 lineal kilometres of the Southeastern Pacific, corresponding to ~9% of length of the
continental Chilean territory.
On board L/M Nueva Galicia two campaigns were
done between January and March (2010). Twenty-three
sites (Fig. 1) were sampled quantitatively (replicated
quadrants) doing SCUBA diving at 5–15 m depth.
The animals obtained in the immersions were sieved
at 0.5 mm and fixed in buffered 5% formaldehyde,
and then they were sorted, preserved in alcohol
70%, identified, measured and photographed, using a
stereo-microscope for the smallest ones.
40
For the identification and characterization
of species (i.e., distribution and taxonomical
observations) Schrödl’s works were mostly used
(Schrödl, 1996a, 2003) and all specific taxonomical
works carried out in the area. In the biogeographical
scope, the distributions were settled as ‘Magellanic
species’ or widespread distribution species, following
the classification of biogeographic ‘provinces’
proposed for the coastal molluscs of Latin America
by Stuardo (1964), the zoogeographic description of
Brattström and Johanssen (1983) and the revision for
the Chilean coast of Camus (2001).
RESULTS
Forty-three individuals belonging to eight
different species were registered; all of them are
new records for the park (Table 1). These correspond
to 15.4% of the total benthic species of gastropods
recorded in the survey (52), and to 3.7% of the total
species of free-living benthic marine non-colonial
invertebrates (Fig. 2).
The family Discodorididae was the best
represented with two species and all the other
families presented one species (Table 1): Acteonidae
(Acteon biplicatus, Fig. 3A), Diaphanidae (Toledonia
perplexa, Fig. 3B), Chromodorididae (Tyrinna nobilis,
Fig. 3C), Discodorididae (Diaulula punctuolata and
D. variolata, Figs. 3D–E, respectively), Flabellinidae
(Flabellina falklandica, Fig. 3F), Onchidorididae
(Acanthodoris falklandica, Fig. 3G) and Tritoniidae
(Tritonia challengeriana, Fig. 3H).
Adding the survey’s sites (PNBO, see Table 1
and Fig. 1) in where the species were registered;
Toledonia perplexa extends its geographical
distribution toward the north and Diaulula variolata
extends its geographical distribution toward the
south (Fig. 4). From a biogeographic point of view
(Fig. 4), 38% of the species showed a Magellanic
distribution: Acteon biplicatus, Toledonia perplexa
and Acanthodoris falklandica; the last one being
distributed until the intermediate area among the
Magellanic and Peruvian provinces. The remaining
62% demonstrated a widespread distribution:
“Peruvian-Magellanic” (Diaulula variolata and
Tyrinna nobilis), “Peruvian-Magellanic-Patagonic”
(Diaulula punctuolata) or reaching Antarctic and
sub-Antarctic regions (Flabellina falklandica and
Tritonia challengeriana).
DISCUSION
Without a doubt, knowledge regarding
Opisthobranchia of southern South America –
particularly on Nudibranchia and Sacoglossa– has
had a notable increase in the last couple of years
through the works of Michael Schrödl (see, for
example, Schrödl, 1996a, 2003; Schrödl and Grau,
2006), María Angélica Fischer (e.g. Fischer and
Ortea, 1996; Fischer, 2006), and Claudia Muniaín
and Ángel Valdés (e.g. Muniaín et al., 1996; Muniaín
and Ortea, 1997; Valdés and Muniaín, 2002; Muniaín
et al., 2007). Nevertheless, there are numerous
groups in which a lack of information still exists, for
example, Cephalaspidea and lower Heterobranchia.
For that reason, the species Acteon biplicatus was
included in this work. In spite of that species not
being a “true opisthobranch”, it was in the “limbo”
of the general taxonomic report carried out on the
gastropods of the Bernardo O’Higgins National
Park.
Species diversity
The taxonomic and distributional database
published on the Chilean molluscs (Valdovinos,
1999) points out the presence of 59 species of
Opisthobranchia (sensu lato, i.e, including Acteonidae
and others) on the latitudinal band 45–55ºS, which
corresponds to the concept “Magellan Region”
given in this work. Subsequently, Schrödl (2003) in
the development of his work where the taxonomic
adjustments of various species were performed,
points out the presence of 34 Nudipleura (sea slugs)
on the extensive area from 41º toward the southern
Strait of Magellan. And finally, Fischer (2006) points
out 44 species of Opisthobranchia (sensu lato) on the
Magellanic Province. The results of our work, which
is adjusted to the latitudinal band 48–52ºS (see Fig.
1), corresponded to 14% of the species pointed out by
Valdovinos (1999), 18% of those by Schrödl (2003)
and 18% of those by Fischer (2006); considering
eight reported species of Opisthobranchia (sensu
lato) compared to Valdovinos’ and Fischer’s works,
and only our six species of Nudipleura compared to
Schrödl’s work.
Although it is certain that the number of species
identified could seem extremely low, this report
presents a considerable number of opisthobranch
species in regard to the total gastropods species
found (~15%, see Fig. 2). Several detailed reports of
molluscs generated in the last years have reported
a low number of opisthobranch species ranging
from 0% to 21% (Table 2). Therefore, our 15%
of opisthobranchs regarding the total gastropods
reported does not represent a low quantity, but rather a
normal value, considering the sampling methodology
and the bathymetric range studied.
41
Figure 3:
Opisthobranchia (sensu lato) from Bernardo O’Higgins National Park: A, Acteon biplicatus; B, Toledonia perplexa; C, Tyrinna nobilis; D, Diaulula
punctuolata; E, Diaulula variolata; F, Flabellina falklandica; G, Acanthodoris falklandica; H, Tritonia challengeriana.
Scale bars: A,B,H= 1 mm; C-G= 1 cm.
42
Table 1:
Opisthobranchia from Bernardo O’Higgins National Park (PNBO), showing stations of occurrence (PNBO stations, see Fig. 1)
and number of individual collected (in parenthesis).
Family
Species
PNBO Station
(and individuals)
Acteonidae
Acteon biplicatus (Strebel, 1908)
6(13); 16(5)
Diaphanidae
Toledonia perplexa Dall, 1902
6(5); 8(1); 16(8)
Chromodorididae
Tyrinna nobilis Bergh, 1898
4(2); 5(2)
Discodorididae
Diaulula punctuolata (d'Orbigny, 1834)
4(1)
Diaulula variolata (d'Orbigny, 1837)
3(2)
Flabellinidae
Flabellina falklandica (Eliot, 1907)
3(1)
Onchidorididae
Acanthodoris falklandica Eliot, 1907
3(1); 16(1)
Tritoniidae
Tritonia challengeriana Bergh, 1884
4(1)
Taxonomical and distributional remarks
Acteon biplicatus is distributed from 43ºS
(Cárdenas et al., 2008) to Tierra del Fuego and
Falkland/Malvinas Islands (Castellanos et al., 1993),
presenting a bathymetric range of 16–152 m (Strebel,
1908). This species presents a similar morphology
to A. elongatus Castellanos, Rolán and Bartolotta,
1987, but both can be differentiated in the fact that
A. elongatus do not have columellar teeth and have a
much more elongated aperture.
Toledonia perplexa is distributed from 48.7ºS
(new record of this study) to Cape Horn (USNM,
2011) and Falkland/Malvinas Islands (Dell, 1990).
With regard to the morphological similarity of this
species, there is a taxonomical problematic with T.
limnaeaeformis, because the diagnostic characters
that separate both species often causes a confusion.
Dell (1990) commented that the main difference
among these species is the more elongated last whorl,
giving a wider abapical extension in T. perplexa.
Although Marcus (1976) figured a specimen of T.
limnaeaeformis with that abapical extension and she
only separates both species in their diameter/height
ratio (60–69% for T. limnaeaeformis and 72–84% for
T. perplexa). Nowadays it is known that T. perplexa
is a Magellanic species and T. limnaeaeformis is a
Kerguelenian species, but there is no real certainty
on the distribution of T. limnaeaeformis, since several
misidentifications were reported on the Magellan
Region (e.g. Dell, 1990; Forcelli, 2000). Therefore,
new comparative records of species of the genus at
intermediate locations should elucidate the affinity
of both species.
Tyrinna nobilis is distributed from Los Hornos,
northern Chile, Juan Fernández Islands, toward the
Chilean and Argentinean Patagonia, reaching the
Valdes Peninsula in the Atlantic coasts (Schrödl et al.,
2005). Despite its widespread distribution, Schrödl
(2003) considers it as a species from the Magellanic
Province, but in our work it is remarked as having a
widespread “Peruvian-Magellanic” distribution (see
Fig. 4). The different species of the genus Tyrinna
43
Figure 4:
Biogeographic distribution of opisthobranchs of Bernardo O’Higgins National Park (PNBO area) embracing the South American continent and the
Falkland/Malvinas Islands. Biogeographic provinces were taken from Stuardo (1964), Brattström and Johanssen (1983) and Camus (2001). Arrows
indicate the continuity of distribution toward Antarctic or sub-Antarctic areas.
were revised by Schrödl and Millen (2001), who
pointed out that along the Chilean coast only Tyrinna
nobilis would exist.
Diaulula punctuolata is distributed from Callao,
Peru (Dall, 1909), toward the Guaitecas Islands
(Odhner, 1926) to the Strait of Magellan (Abraham,
1877); reaching Atlantic coasts, the Falkland/
Malvinas Islands (Eliot, 1907) and Argentinean
Patagonia (Schrödl, 1996a, 1999a). Various works
focussed on this species have been carried out (e.g.
44
Bergh, 1898; Marcus, 1959; Millen, 1982; Schrödl,
1996a, 1996b), being the anatomical study of Valdés
and Gosliner (2001) the last taxonomic adjustment
and assignment in the genus Diaulula.
Diaulula variolata is distributed from Arica,
Chile (Schrödl, 2003), toward southern Chile (Zagal
and Hermosilla, 2007) up to 51ºS (new record of
this study). This species, just as D. punctuolata, was
studied by several researchers (e.g. Bergh, 1898;
Marcus, 1959; Millen, 1982; Schrödl, 1996a, 1996b)
Table 2:
studies
where subtidal
were collected.
Opisthobranchia
recordedsamples
in malacological
reports since 1970 in the Pacific side of the Magellanic Province
(i.e. fjords and channels region), taking into account studies where subtidal samples were collected.
Report
Latitude and depth
Number of species
Total Gastropoda Opisthobranchia
Dell (1971)
40.5–55.9ºS; 0–32m
38
0 (0%)
Reid and Osorio (2000) 45.6–46.7ºS; 0–15m
33
2 (6.1%)
Linse (2002)*
45.1–55.8ºS; 8–2505m
42
2 (4.8%)
Ríos et al. (2003)
52.6–52.8; 30–50m
38
3 (7.9%)
Osorio and Reid (2004) 43.7–46.5ºS; 0–330m
7
1 (14.3%)
Osorio et al. (2005)
43.7–46.5ºS; 0–330m
19
4 (21.1%)
Ríos et al. (2005)
48.0–53.9ºS; 24–732m
8
1 (12.5%)
Osorio et al. (2006)
43.7–45.8ºS; 62–345m
30
3 (10%)
Ríos et al. (2007)
53.0–53.6ºS; ~8m
9
0 (0%)
Cárdenas et al. (2008)
45.6–46.7ºS; 22–353m
39
2 (5.1%)
Ríos et al. (2010)
52.3–52.5; ~16–~61m
1
0 (0%)
This survey
48.7–51.5ºS; 5–15m
52
8 (15.4%)
*Only shelled molluscs were considered in this review.
due to the taxonomical problematic that it presented
(see Schrödl, 2003), and finally it was validated as D.
variolata (Valdés and Gosliner, 2001).
Flabellina falklandica is distributed from the
Chiloé Island, Chile, toward the Strait of Magellan and
Tierra del Fuego, Falkland/Malvinas, South Georgia
and Crozet Islands (Schrödl, 2003). In the same work
two additional species of the genus were recognized
as found on the Chilean coast (Flabellina sp.1 and
Flabellina sp.2), highlighting that there was an ongoing
revision of the genus on the South Pacific coast; their
results have, however, not been published yet. Ramirez
et al. (2003) recorded Flabelina (sic) cf. falklandica for
Peruvian sea, but that record requires confirmation,
given that Flabellina sp.2 is distributed from Ancón,
Perú, toward central Chile (Schrödl, 2003) and F.
cerverai Fischer, van der Velde & Roubos, 2007 was
described for Coquimbo, northern Chile.
Acanthodoris falklandica is distributed from
Coliumo Bay, Chile (Schrödl, 1996a; 1997a), toward
the Chilean Patagonia (Odhner, 1926; Marcus 1959), to
Cape Horn and the Falkland/Malvinas Islands (Schrödl,
2003). This species has been associated to the brown
kelp Macrocystis pyrifera (see Schrödl et al., 2005).
Consequently, a specimen of our study was collected in
a dense meadow of M. pyrifera (Palacios, pers. com.).
45
Tritonia challengeriana presents a widespread
distribution from Ancud Bay, Chile (Schrödl, 1996a)
toward the Chilean and Argentinean Patagonia
(Schrödl, 1996a; 1996b), Falkland/Malvinas Islands
(Eliot, 1907) to the Antarctica (Schrödl et al., 2005).
This specie presents an external similarity to T.
odhneri Marcus, 1959, but T. odhneri differs because
it presents some white lines along the foot and at the
gills (see Schrödl et al., 2005). In addition, T. odhneri
inhabits exposed sectors with strong currents, while
T. challengeriana inhabits both protected and exposed
fjords (Schrödl et al., 2005). In our study it was
collected in a station with low exposure (pers. obs.).
Final considerations
Although this report represents a progress in
knowledge of the marine fauna of the park, the species
scarcely represent about 13% of the total known species
of gastropods in the park after the study (including those
not found in the sampling) and 14% of opisthobranchs
known in the latitudinal band 45–55ºS. Therefore,
more intensive studies are necessary in all bottoms to
improve the malacologic knowledge of the area.
ACKNOWLEDGEMENTS
We would like to thank our colleagues who supported
us collecting samples used in this study, as well as the
crew of L/M Nueva Galicia for their assistance. To
Américo Montiel (University of Magallanes, Chile) and
Jesús Troncoso (University of Vigo, Spain) we thank for
aiding us in technical facilities. Finally we would like to
thank Gonzalo Rosenfeld and Beatriz Alvarado for their
kind translation revisions of the English language and
two anonymous referees of the manuscript. This work
was carried out starting from the project “Territorial
characterization of the Bernardo O’Higgins National
Park: its economic, tourist, scientific and cultural
potential” (INNOVA-CORFO 08CTU01-20); which
was developed by CEQUA Foundation and Chilean
National Forest Corporation (CONAF), and supported
by the Chilean Production Development Corporation
(CORFO).
46
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Thalassas, 27 (2): 49-60
ANATOMICAL DESCRIPTION AND BIOLOGY OF THE
SPLANCHNOTROPHID Splanchnotrophus gracilis HANCOCK
& NORMAN, 1863 FOUND PARASITIZING THE DORIDACEAN
NUDIBRANCH Trapania tartanella IHERING, 1886 AT THE RÍA DE
FERROL (GALICIA, NW IBERIAN PENINSULA)
ABAD M.(1), DÍAZ-AGRAS G.(1) & URGORRI V. (1,2)
Key words: Splanchnotrophus gracilis, Trapania tartanella, SEM, anatomical description, infection rate, parasitic load, host damage.
ABSTRACT
The genus Splanchnotrophus (Copepoda,
Poecilostomatoida, Splanchnotrophidae) is a small
group of endoparasites infesting certain shell-less
marine opisthobranchs. The present study is focused
on the type species Splanchnotrophus gracilis
Hancock & Norman, 1863 and its relationship with its
host, the doridacean nudibranch Trapania tartanella
Ihering, 1886. This nudibranch presents large
populations at the Ría de Ferrol, frequently found
on the porifera Desmacidon fructicosum with a large
part of specimens parasitized. The parasite female
is exteriorly visible due to the presence of ovigerous
sacs. In most of the nudibranchs the parasite can be
directly observed through the almost transparent
integument of the host. The females, much larger than
(1) Estación de Bioloxía Mariña da Graña, Universidade de
Santiago de Compostela, Rúa da Ribeira, 1 (A Graña), 15590,
Ferrol. [email protected], [email protected].
(2) Departamento de Zooloxía e A. Física, Universidade de
Santiago de Compostela, Campus Sur, 15782, Santiago de
Compostela. [email protected]
the males and with a highly modified anatomy, take
up the posterior body cavity of T. tartanella, clutching
the gonad and digestive gland with their long body
appendages. Males move freely within the interior
of the body of the host, although they preferably
position themselves near the female and along the
reproductive system of the nudibranch. Generally,
at least a single female of S. gracilis appears per
nudibranch specimen. In the case of males, they
appear in a number varying from 1 to 4.
The collection of specimens was carried out by
means of autonomous diving. In the present work a
description of the species Splanchnotrophus gracilis
using Scanning Electronic Microscopy (SEM) and
light microscopy is presented. New data on the
biology of this species is given. High infection rates
(94%) and parasitic loads (up to 43 parasites per
host) were found. No clear damage has been found
in the infected viscera of T. tartanella or during the
reproductive process, as normal copulations and
spawns were observed in lab conditions. However,
data suggest that a higher mortality exists in those
specimens presenting a higher parasite load.
49
ABAD M., DÍAZ-AGRAS G. & URGORRI V.
Figure 1:
Ría de Ferrol map, showing the sampling area (black circle).
INTRODUCTION
The family Splanchnotrophidae (Copepoda,
Poecilostomatoidea) is a poorly known group of highly
modified endoparasites on marine opisthobranchs.
23 species belonging to five genera are currently
known: Splanchnotrophus Hancock & Norman, 1863,
Lomanoticola Scott & Scott, 1895, Ismaila Bergh,
1867, Ceratosomicola Huys, 2001, and Arthurius
Huys, 2001 (Salmen, 2010).
Historically, little attention has been paid to
this parasitic group. The first works date back to
the 19th century (Hancock & Norman 1863; Bergh
1868, 1898; Hetch 1893, 1895) and they are brief
descriptions with sketchy habitus drawings. In the
20th century some works (Delamare-Deboutteville,
1950; Belcik, 1981) were focused on this group, but
they followed some confused data of the precedent
authors and they paid little attention on cephalic
appendages (except: Laubier, 1964) and their tiny
structures. Schrödl (1997, 2002) published solid
new data on splanchnotrophid parasitism in Chilean
opisthobranchs from the genus Ismaila. But it was not
until the review of the family done by Huys (2001)
when the “taxonomic myopia” surrounding this group
was solved, thanks to the detailed light microscopy
descriptions and drawings. Huys gathers all those
endoparasites on marine opisthobranchs, except for
those belonging to the genus Briarella (Salmen et
50
al., 2010), in the family Splanchnotrophidae, which
now comprises five genera: Splanchnotrophus,
Lomanoticola (splitted from the latter), Ismaila,
Arthurius and Ceratosomicola. Shortly after Haumayr
& Schrödl (2003) introduced the Scanning Electronic
Microscopy (SEM) as a new and suitable tool to study
tiny structures in great detail, giving new light on
the study of these parasites. Very recently, Salmen et
al. (2008a, b) used this technique successfully when
they described new species belonging to the genera
Ceratosomicola and Arthurius.
Like other poecilostomatoids, splanchnotrophids
have a sickle-shaped mandible. There are also
some common characteristics shared by all species
belonging to the family Splanchnotrophidae: 3segmented antenna, 2- segmented maxilla, second
and third biramous thoracopods and one pair of
caudal rami (Huys, 2001).
Splanchnotrophids show a remarkable sexual
dimorphism concerning body size and shape (Huys,
2001; Haumayr & Schrödl, 2003): females are
much bigger than males, with a highly modified
body and having 3-6 pairs of lateral processes with
three possible functions (Salmen et al., 2008a): the
first consists in wrapping the inner host organs,
the second in holding the ovotestis branches (white
strings of newly formed eggs shining through the
tissue can be easily observed) and finally, the third
ANATOMICAL DESCRIPTION AND BIOLOGY OF THE SPLANCHNOTROPHID Splanchnotrophus gracilis HANCOCK & NORMAN, 1863 FOUND
PARASITIZING THE DORIDACEAN NUDIBRANCH Trapania tartanella IHERING, 1886 AT THE RÍA DE FERROL (GALICIA, NW IBERIAN PENINSULA)
Figure 2:
A. T. tartanella parasitized by a S. gracilis female. B. T. tartanella parasitized by a S. gracilis female and several males. C, D. Desmacidon
fructicosum. ap: lateral appendages; es: egg sacs. ParFem: parasite female; ParMal: parasite male.
consists in extending the body surface in order
to facilitate the breathing as the gas exchange
is improved. Males are dwarf, with the typical
ciclopoid body shape and do not show any lateral
process. But this sexual dimorphism is not seen
concerning the cephalic appendages, which have
the same or nearly the same structure in both sexes
(Huys, 2001; Haumayr & Schrödl, 2003; Salmen et
al., 2008a, b).
The females are situated inside their hosts with
the lateral processes embracing the inner organs
(usually gonads or kidney) and the males are normally
situated close to the females or lying freely in the
body cavity of the host (Huys, 2001; Salmen 2005).
Except for some of the species belonging to the genus
Ismaila (Schrödl, 1997, 2002; Haumayr & Schrödl,
2003) the members of the Splanchnotrophidae do not
cause a visible damage on their host, except those
related with the space competition with the inner
structures of the host.
The genus Splanchnotrophus was established by
Hancock & Norman in 1863. Until the review of the
family by Huys (2001), Lomanoticola was believed to
belong to Splanchnotrophus, but this author gives it
genus category, so the old Splanchnotrophus genus is
divided in Splanchnotrophus s.s and Lomanoticola.
Splanchnotrophus currently possesses 4 species
distributed in the Mediterranean Sea and in the
European Atlantic: S.gracilis, S. angulatus, S. willemi
and S. dellachiajei.
51
Figure 3:
S. gracilis female. A. Habitus (light microscopy). B. Egg sac (light microscopy). C. Cephalic appendages (SEM). D. Second thoracopod (SEM). E.
Third thoracopod (SEM). F. Abdomen, bearing caudal rami, genital openings and anal slit (SEM).
aa: antenna; an: antennule; ao: anal opening; ap: lateral appendages; cr: caudal rami; ed: endopodit; es: egg sacs; ex: exopodit; go: genital
opening; la: labium; lr: labrum; ma: maxilla; md: mandible.
52
The present work shows the results obtained
during a research project carried out by the Estación
de BIoloxía Mariña da Graña (EBMG) focused on the
species Splanchnotrophus gracilis. High infection
rates were discovered for the doridacean host Trapania
tartanella at the Ría de Ferrol (Galicia, NW Península
Ibérica). An anatomical description using SEM is
given, as well as infection rates, parasitic loads and
other biological aspects. All these data are critically
compared and discussed taking into account previous
works (Schrödl, 1997, 2002; Huys, 2001; Haumayr &
Schrödl, 2003; Salmen et al. 2008a, b, 2010).
Collecting
Infected nudibranchs were collected by scuba diving
during the two last years in the sampling area, situated
next to the location known as Fornelos, at the Ría de
Ferrol (coordinates 43º 28’ 02,16” N, 008º 14’ 47,70”
W) (Fig.1). Three samplings were made in these years.
T. tartanella were found feeding upon the porifera
Desmacidon fructicosum (Fig. 2 C, D), usually at 15 to
20 m depth. Then the specimens were observed in the
laboratory under a binocular microscope searching for
the parasites, and some photos were taken with a camera
coupled in a binocular microscope. Most specimens
were anaesthetized in a 7% MgCl2 solution and then
fixed in 70% ethanol, absolute ethanol (for further
molecular analysis), Bouin solution or in 4% formalin
seawater (for histological studies).
Some specimens were kept alive in aquariums
with D. fructicosum and their behaviour was observed.
Others were left in a Petri dish in starvation, with two
water changes per day.
More specimens studied were taken from the
Opisthobranch collection of Victoriano Urgorri, where
they were preserved to date in 70% ethanol. He
sampled by scuba diving several times in the years
1992 and 1996 in the same location as those made
between 2009 and 2010.
Dissections
Those T. tartanella that were kept alive were
vivisected after one hour in a 7% MgCl2 solution with
the aim of obtaining living parasite specimens and an
observation in vivo. The extraction process took place
under a binocular microscope. Photos and videos of
the living parasites were taken. Afterwards S. gracilis
specimens were fixed in 70% ethanol.
The dissection of the previously fixed T. tartanella
specimens was like the vivisection process, but photos
were not taken. The position, number and developmental
stadium of the parasites on the host were recorded, as the
inner organs of T. tartanella were observed in searching
for any present potential damage.
SEM
Cleaning process was made with an ultrasonic
device during 3 minutes in water with organic detergent.
Due to the shrinking problems observed following
the acetone dehydration method previously used
(Haumayr & Schrödl, 2003; and Salmen et al. 2008a,
b) a new methodology based on a lyofilization (freezedrying) process was developed: after an immersion of
10 minutes in liquid nitrogen, the specimens were
lyofilized for at least 12 minutes.
Before SEM microscopy, samples were coated
with gold. Afterwards they were observed under
electronic microscopy and photos were taken.
Light microscopy: For males, the results obtained with
SEM were completed with light microscopy observations.
Terminology: The terminology used here is adopted from Huys (2001), Haumayr & Schrödl (2003),
and Salmen et al. (2008a, b). Terms as cephalothorax
(five head segments fused with the first thoracic
segment), thorax and abdomen describe the body segmentation. It is also assumed that splanchnotrophids
lack first thoracopods (Ho, 1987).
53
Figure 4:
S. gracilis male. A. Habitus (SEM). B. Cephalic appendages (SEM). C. Mouthparts detail. D. Second thoracopod (SEM). E. Third thoracopod
(SEM). F. Anal somite and caudal rami (SEM). F. Long caudal rami seda detail, showing the spines (SEM).
aa: antenna; an: antennule; as: anal somite; cr: caudal rami; ed: endopodit; ex: exopodit; gs: genital somite; la: labium; lr: labrum; ma: maxilla;
md: mandible; ml: maxillule; se: seda; thp 2, 3: thoracopods 2,3.
54
RESULTS
Description:
Class Copepoda H.M. Edwards, 1840
Order Poecilostomatoida Thorell, 1859
Family Splanchnotrophidae Norman & Scott, 1906
Genus Splanchnotrophus Hancock & Norman, 1863
Splanchnotrophus gracilis Hancock & Norman, 1863
Material examined: 14 females and 20 males
collected from August 2009 to September 2010.
Station: Fornelos (Ría de Ferrol, Galicia, NW Iberian
Peninsula).
Female: (Fig. 3A)
Compact body, measuring from 0.7 mm to 1 mm
in length.
strong spine on the distal edge where they fit with
the next segment; third segment with four spines,
one long and three short, one with a hole on its basis.
Labrum bilobate, larger than the labrum.of the male.
Mandible with thick and strong base, it recurves on a
sickle-shaped blade with 3-4 teeth. Maxillule is fused
with mandible base; it shows a little seta in the apex. It
is usually covered by the mandible and hard to detect.
Maxilla 2-segmented, first longer and thicker, holds
the second one, which is shorter and ends apically
with two strong setae. Labium shows a great amount
of hair. Cephalic appendages can be retracted when
the animal is disturbed.
First thoracopod absent. Second thoracopod (Fig.
3D) is biramous, exopodit much longer, with three
spines; endopodit much shorter than exopodit. Third
thoracopod (Fig. 3E) as the second one. Fourth
thoracopod not detected.
Segmentation:
The cephalothorax comprises the five cephalic
segments (each of them with a pair of cephalic
appendages) and first thoracic segment. Thorax with
second and third segments enlarged. They bear three
pairs of long (1.5-2 mm) lateral processes ending in
a thin tip.
Abdomen (Fig. 3F) showing genital openings
laterally disposed and bearing a pair of bilobate,
kidney shaped egg sacs (Fig. 3E). Caudal rami (Fig.
3F) short, with six small setae all around it and one
long seta at the apex. Anal slit between the caudal
rami.
Male (Fig. 4A):
Fourth thoracic somite with one pair of lateral
outgrowths. It is not clear if there is a fifth thoracic
segment, as it can be retracted and segments edges
are difficult to see. Abdomen short, one segmented,
bearing caudal rami and the anal and genital
openings.
Cephalic appendages (Fig. 3C):
Antennule 2-segmented, first segment with two
strong spines, while second shows two constrictions
that divides it in proximal, medial and distal part:
proximal with two spines and one seta, medial with
two short and one long seda; and distal with at least
ten setae, three short and the other ones longer.
Antenna 3-segmented, two first segments with a
Body ciclopiform, elongate and measuring from
0.40 mm to 0.70 mm in length.
Segmentation:
Cephalothorax comprises five cephalic segments
and first, second and third thoracic (second and third
longer than first). Thorax comprises the last three
thoracic segments (from fourth to sixth), with the
same size. Abdomen 2-segmented: the first segment
is the genital somite and the second is the anal somite
(both with similar size). Genital somite bears two
genital lobes (each one with three seda decreasing in
size). Anal somite presents the caudal rami with the
anal opening between them.
55
Table 1:
Infection rates in each sampling and total infection rate for all samplings.
Sampling date Collected,nfecte
02/08/92
22
19
86.3 %
21/08/92
3
2
66.6%
23/08/92
3
2
66.6%
01/08/96
4
2
50%
05/08/96
3
3
100
05/08/09
85
81
98.4%
24/05/10
18
18
100%
20/09/10
6
6
100%
TOTAL
144
133
92.3%
Cephalic appendages (Fig.4B, C): Like in the
female, but no hole on the third segment of the
antenna; male labrum smaller in proportion to other
cephalic appendages than in the female.
First thoracopod absent. Second thoracopod
(Fig.4D) biramous, with a little seta on protopodit.
Exopodit longer and thicker, with five or six little
spines in the distal portion; apex ending in a blister
where a long and curved process starts. Endopodit
small and thin, with a little spine on the distal portion.
Third thoracopod (Fig.4E) biramous, without any seta
on the protopodit. Exopodit longer and thicker, very
similar to that of the second thoracopod, but with the
blister more reduced and a shorter process. Endopodit
shorter than exopodit, but longer and thicker than
that of the second thoracopod, without distal spine.
Fourth thoracopod very short and thin, with a small
constriction on the medial portion. Fifth and sixth
thoracopod: absent.
Caudal rami (Fig. 4F, G): Robust, they are
located on the second abdominal segment (anal
somite); with six or seven small setae, except for the
one which is very long and presents its last third part
pinnate.(Fig. 4G).
56
Infection rate
Biology
Infection rates: They are shown in table 1 and
they are divided in samples, showing sampling
date, individuals collected and individuals infected.
Finally, the total infection rate on all the samplings
is given.
Table 1 only shows the results obtained during the
most favourable months to find the host of the parasite
(from May to September) as no individuals of T.
tartanella were found at the sampling locality during
winter samplings (from October to April).
Position in the host: Females show a typical
position inside the host, with their lateral processes
wrapping the gonad, from the posterior cavity of the
nudibranch to the most anterior part, where the tips of
the processes are ravelled with the tubular portions of
the reproductive apparatus of the host (Fig. 2A). They
pierce the body of the nudibranch with their urosoma
at the level of the anal papilla, among the gills and
show a pair of white and kidney-shaped egg sacs.
The anterior part of the female is located towards the
ventral portion of the host with the mouthparts close
to the gonad but not in contact with it.
During dissections two exceptions to this
positioning general rule were found. In one case
three females were inside the host: one showing
the “most frequent” position but the urosome was
not protruding the intertegument; another one was
located between the first one and the gonad of the
host, and seemed to be in a juvenile stadium; and
the third one was ovigerous and embraced the gonad
ventrally with the lateral processes, the urosome
protruded the intertegument at the left medial part
of the host and the mouthparts were close to the right
part of the gonad. The other case is very similar,
but there were four females: three were in the same
position as the anterior case, except for the female
that was located between the “most frequent” one and
the gonad, which was more developed and “inverted”;
the fourth one was lying in the posterior cavity and
seemed to be juvenile.
due to the great likeness between these stages. In table
2 minimum and maximum parasitic loads found in the
different samplings are shown. No distinction between
females, males or copepodit stages was made.
Regarding the males, they show more plasticity
when positioning themselves inside the host and
referring to their number per host, but they can be
usually found lying freely in the posterior cavity of
the nudibranch, close to the female (Fig. 2B). Other
positions frequently observed are the reproductive
apparatus, the ventral side of the gonad, the interior
of the prebranchial tentacles and pericardium. It
was observed in two cases that mature males were
situated embedded between the first and second
lateral processes of the female. Their ventral side
was situated towards the gonad of the host and fixed
to it.
Lateral outgrowths: some females showed a bulky
pair of lateral outgrowth, while in other cases the
shape was more flattened.
Parasitic load
This measure is defined as the number of parasites
per host. At least one female was always found in the
infected nudibranch hosts. Males were not always
found (in 45 cases of the total nudibranchs dissected),
and they usually appear in a number between 1 and 4.
In some cases (those corresponding to the sampling of
May) more parasite specimens, which could be males
or copepodits, were found in high number, despite
being very difficult to differentiate between the two
Intraspecific variability
Females: Structures with taxonomic value, as
cephalic appendages or thoracopods did not show any
variability between the specimens studied, but some
variability was found in other structures:
Lateral appendages: in those cases where the
lateral appendages were found ravelled with the
genital apparatus of the host, they ended tapering to
a soft hooked tip; in other cases their length was not
enough to rise the genital apparatus of the host, and
the tips of the appendages were blunter.
Males: The only intraspecific variability found
between males was the length of the pinnated portion
of the long seta of the caudal rami.
Host damage
No evident damage was found in the inner organs
of the host, except for one case where the gonad was
reduced. Parasitized and non parasitized T. tartanella
show gonads of the same size. Normal nudibranch
copulations and spawns were observed. But some
indirect damage was found in starvation conditions:
those T. tartanella with a higher parasitic load died
before those with only a couple of parasites.
A strange phenomenon was also observed in
starvation conditions: in four T. tartanella, after more
than 21 days in the Petri dish, the parasite females
broke with their dorsal side the intertegument of the
host and went out freely in the water; the nudibranchs
died in a time lapse between the next 1-5 hours.
57
Table 2:
Maximum and minimum parasitic loads (parasites per host) in each sampling. No distinction between females, males or copepodit stages was made.
Sampling data
Minimum parasitic load
Maximum parasitic load
02/08/92
1
14
21/08/92
1
3
23/08/92
1
4
01/08/96
1
2
05/08/96
1
4
05/08/09
1
5
24/05/10
1
43
20/09/10
Not dissected
Not dissected
DISCUSSION
Anatomical description:
The species is identified as Splanchnotrophus
gracilis Hancock & Norman, 1863 due to the
following facts:
The males found in the present work show a high
resemblance with that redescribed by Huys (2001)
concerning body shape, segmentation, cephalic
appendages and thoracopods.
Salmen made a detailed description of this species
in her thesis of 2005 using SEM, which coincides
with the results of this work. Body shape and size,
segmentation, cephalic appendages and thoracopods
fine structure, positioning inside the host and parasite
number per host are mostly the same as described
here. The slight differences found (parasitic load,
male caudal rami) could be explained thanks to the
high numbers of specimens collected and studied in
the present work.
The nudibranch host, Trapania tartanella,
coincides with those that Salmen (2005) describes
for the first time holding this parasite species.
58
In addition, the sampling point belongs to the
biogeographical distribution described by Schrödl
(2002) for the genus Splanchnotrophus (Eastern
North-Atlantic).
The male of this species is very similar to that of
S. angulatus, but they can be distinguished thanks
to the presence in S. gracilis of three setae in their
genital segment and to the concave shape of the edges
of this segment (Huys, 2001).
Biology
The total infection rate (92.3%) is very high and
shows one of the biggest infection prevalence on one
specific opisthobranch species. Other high infection
rates found were those described by Schrödl in the
Chilean nudibranch species Thecacera darwini (89100%) and Okenia luna (70%), and the sacoglossan
Elysia patagonica (89%) (Schrödl, 2002).
Nothing can be said about the seasonal infection
rate variation, due to the fact that all T. tartanella
recollections were made in the time lapse between
the months of May and September, those months
when the water increases its temperature and there
seem to be the most favourable conditions for the
growth of the nudibranch host populations. This idea
is supported by the fact that during the collecting
divings in the winter (from October to April) not
a single T. tartanella specimen was found. To add
more complications, few data exists concerning the
host biology, except for that focused on its feeding
behaviour (McDonald & Nybakken, 1996). What is
stated below strongly suggests that further studies
on the seasonal abundance of the splanchnotrophids
first require solid knowledge on its opisthobranch
host biology.
Positions found inside the host match those
described by Huys (2001) and Salmen (2005), and
some new ones for the males are given. An interesting
condition is shown in the two cases where the adult
male was in contact with the female and embedded
between its first and second lateral appendages. One
hypothesis to explain this positioning could be some
kind of precopulatory behaviour, but more data are
required to support it.
Regarding parasitic load, results show a clear
seasonal variation, with the maximum load in May
(43). During this period, the parasite load comprises
both adult males and females and copepodit stages.
In August, the number of parasites per host is
stable (except in the 02/08/92 sampling) and all the
specimens were adult parasites. According to the
preceding data it could be suggested that during the
period of April-May the infection processes are at
their highest levels. This hypothesis is supported
by the fact that four other T. tartanella showed high
parasitic loads during the same sampling (39, 33, 26
and 23 parasites); and this surprising parasitic load
is coincident with the biggest annual growth in the
population of T. tartanella. Anyway, it is necessary
to find more infected host specimens during the non
recorded months (April, June and July) to follow
the progress of the parasitic load. The nudibranch
species with the highest parasitic load found so far
was one specimen of the giant Dendronotus iris
recorded by Ho (1981) with 425 Ismaila occulta
individuals.
Although some intraspecific variability was found
(lateral appendages and outgrowths of the female and
caudal rami of the male) the studies are limited to a
few individuals of the total. The variability found on
the lateral outgrowths coincides with that expected
by Huys (2001) for the genus Splanchnotrophus: it
might show intraspecific variability concerning the
prosomal region and lateral outgrowths.
Concerning host damage, the results set out here
match in two ways with those set out in the 1997
paper of Schrödl. First, nudibranchs with higher
parasitic loads seem to show a higher mortality under
starvation conditions; and second, in two cases the
nudibranch host was killed due to the wounds caused
by the female when it exits the host. This phenomenon
was observed for the first time by Schrödl (1997) in
the nudibranch Flabellina sp. 1 parasitized by Ismaila
damnosa. But the gonad reduction and reproductive
cessation noted by Schrödl (1997) were not observed
in the present study, due to the normal copulas and
spawns observed. This suggests that S. gracilis may
probably be better adapted than the Chilean Ismaila
species to its nudibranch host.
ACKNOWLEDGEMENTS
Authors wish to thank Michael Schrödl and
Enrico Schwabe (Zoologische Staatssammlung
München) for their kindly and huge bibliographic
support. Thanks too to the EBMG (USC) partners
and the Biodiversidade e Recursos Mariños Research
Team (USC), for their disinterested helping during
diving collections and SEM preparations.
REFERENCES
Belcick F.P. (1981).The male of Ismaila monstrosa Bergh,
1867. (Copepoda, Splanchnotrophidae). Crustaceana
40: 16-25.
Bergh L. S. R. (1868). On Phidiana lynceus and Ismaila
monstrosa. Annals and Magazine of Natural History
(4) 2: 133-138.
Bergh L. S. R. (1898). Die Opisthobranchier der Sammlung
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Plate. Zoologischer Jahrbücher, Supplement 4: 481-582.
Delamare-Deboutteville C. (1950). Contribution a la
connaissance des copepods du genre Splanchnotrophus
Hancock et Norman parasites des Mollusques. Vie et
Milieu 1/1: 74-80.
Hancock A. & Norman, A., M. (1863). On Splanchnotrophus,
an undescribed genus of Crustacea, parasitic on
nudibranchiate Mollusca. Transactions of the Linnean
Society of London, Zoology 24: 49-60.
Haumayr U. & Schrödl, M. (2003). Revision of
the endoparasitic genus Ismaila Bergh, 1867,
with description of eight new species (Copepoda,
Poecilostomatoida, Splanchnotrophidae). Spixiana
26/1: 1-33.
Hecht E. (1893). Note sur un nouveau Copépode parasite
des Nudibranchs. Archives de zoologie expérimentale
et générale (3) 1, notes et revue: XIII-XVI.
Hetch E. (1895). Contribution à l´étude des Nudibranchs.
Mémoires de la Société zoologique de France 8: 539711.
Ho J. (1981). Ismaila occulta, a new species of
poecilostomatoid copepod parasitic in a dendronotoid
nudibranch from California. Journal of Crustacean
Biology 1: 130-136.
Ho J. (1987). Larval stages of Ismaila occulta Ho, 1981
and the affinity of Splanchnotrophidae (Copepoda:
Poecilostomatoida). Researches on Crustacea 16: 67-83.
Huys R. (2001). Splanchnotrophid systematics: a case of
polyphyly and taxonomic myopia. Journal of Crustacean
Biology 21/1: 106-156.
Laubier L. (1964). La morphologie des pieces bucales
chez les Splanchnotrophidae (Copépodes parasites des
Mollusques). Crustaceana 7: 167-174.
Salmen A. (2005). Morphology, taxonomy and biology
of endoparasitic copepods in shell-less opisthobranch
gastropods (Crustacea, Copepoda, Poecilostomatoida).
Technische Universität München, München.
Salmen A., Wilson N. G. & Schrödl M. (2008a). Scanning
electron microscopical description and biology of
three new endoparasitic Ceratosomicola species from
tropical Indo-Pacific nudibranch hosts (Crustacea,
Copepoda, Poecilostomatoida, Splanchnotrophidae).
Spixiana 31/1: 47-69.
Salmen A., Kaligis F., Mamangkey G. F. & Schrödl M.
60
(2008b). Arthurius bunakenensis, a new tropical IndoPacific species of endoparasitic copepods
from a sacoglossan opisthobranch host (Crustacea,
Copepoda, Poecilostomatoida, Splanchnotrophidae).
Spixiana 31/2: 199-205.
Salmen A., Anton, R. Wilson N. G. & Schödl M. (2010).
Briarella doliaris spec. nov., a new philoblennid
copepod parasite from Australia: a potential link to the
Splanchnotrophidae (Copepoda, Poecilostomatoida).
Spixiana 33/2: 19-26.
Schrödl M. (1997). Aspects of Chilean Nudibranch Biology:
effects of Splanchnotrophid copepod parasitism on
Flabellina sp. 1. Opisthobranch Newsletter 23: 45-47.
Schrödl M. (2002). Heavy infestation by endoparasitic copepod crustaceans (Poecilostomatoida:
Splanchnotrophidae) in Chilean opisthobranch gastropods, with aspects of splanchnotrophid evolution.
Organisms, Diversity and Evolution 2: 19-26.
Thalassas, 27 (2): 61-75
HISTOLOGICAL AND ULTRASTRUCTURAL
CHARACTERISATION OF THE STOMACH AND
INTESTINE OF THE OPISTHOBRANCH Bulla striata
(HETEROBRANCHIA: CEPHALASPIDEA)
ALEXANDRE LOBO-DA-CUNHA(1,2,3), ANA RITA MALHEIRO(4), ÂNGELA ALVES(1), ELSA OLIVEIRA(1),
RITA COELHO(3) & GONÇALO CALADO(3,5,6)
Key words: Digestive tract, microscopy, histochemistry, cytochemistry, Mollusca, Gastropoda
ABSTRACT
In order to obtain more data for a comparative
analysis of the digestive system in opisthobranchs, the
stomach and intestine of Bulla striata were studied
with light and electron microscopy. A 3D-model of
the stomach and its connections with the posterior
oesophagus, digestive gland ducts and intestine
was created from a series of histological sections.
The U-shaped stomach is just a segment of the
digestive tube without any external distinction from
(1) Laboratory of Cell Biology, Institute of Biomedical Sciences
Abel Salazar (ICBAS), University of Porto, 4099-003 Porto,
Portugal. E-mail: [email protected]
(2) Centre of Marine and Environmental Research (CIIMAR),
4050-123 Porto, Portugal
(3) Portuguese Institute of Malacology (IPM), 8201-864 Guia,
Portugal
(4) Vale do Sousa Higher School of Health - CESPU,
Paredes - Portugal.
(5) Lusophone University of Humanities and Technologies,
1749-024 Lisbon, Portugal
(6) Institute for Marine Research (IMAR), FCT/UNL, 2829-516
Caparica, Portugal
the intestine. Internally, the stomach is characterized
by the presence of a typhlosole and many mucussecreting cells that are strongly stained by PAS
reaction and alcian blue. Significant amounts of
proteins were not detected in the mucus-secreting
cells of the stomach, but protein-rich secretory
material was found in the apical region of another
type of secretory cells present in both stomach
and intestine. The end of the typhlosole can be
considered the transition point between the stomach
and intestine. Mucus-secreting cells are also abundant
in the intestine and all of them stain with alcian blue.
However, most mucus-secreting cells of the intestine
are not significantly stained by PAS reaction, but
contain more proteins than the mucus-secreting cells
of the stomach. The granular cells with a large number
of small electron-dense secretory vesicles containing
proteins and neutral polysaccharides were found only
in the intestine. The available data show that despite
some anatomical and histological differences several
cell types are identical in the digestive systems of
Aplysia depilans and B. striata.
61
ALEXANDRE LOBO-DA-CUNHA, ANA RITA MALHEIRO, ÂNGELA ALVES, ELSA OLIVEIRA, RITA COELHO & GONÇALO CALADO
Figure 1:
Anatomy of the stomach and intestine of B. striata. A. Tip of the digestive gland (dg) including the stomach (st) and initial part of the intestine (in).
Terminal portions of the posterior oesophagus (po) and long digestive gland duct (ld) are also visible. B-D. Frontal, lateral and rear views of a
3D-model of the U-shaped stomach (st) and initial part of the intestine (in). A short digestive gland duct (sd) can be seen behind the terminal portion
of the posterior oesophagus (po). The arrowhead mark, approximately, the zone where the stomach typhlosole ends.
INTRODUCTION
In recent years, molecular approaches have been
used to investigate opisthobranch phylogeny (Wägele
et al., 2003; Grande et al., 2004; Vonnemann et al.,
2005; Malaquias et al. 2009a; Dinapoli & KlussmannKolb, 2010; Jörger et al., 2010). Due to these efforts, a
new vision of the relationships among opisthobranch
clades, and between these and other heterobranch
gastropods is now emerging. The molecular data
do not support the monophyly of the traditional
opisthobranchs, but a clade (Euopisthobranchia)
62
comprising the Umbraculoidea, Cephalaspidea,
Runcinacea, Anaspidea (or Aplysiomorpha) and
Pteropoda has received a good support (KlussmannKolb et al., 2008; Dinapoli & Klussmann-Kolb,
2010; Jörger et al., 2010). In this clade diets are
very diversified: umbraculoideans feed on sponges,
anaspideans and runcinaceans are herbivores,
pteropods can be carnivores (Gymnosomata) or
omnivores (Thecosomata), and cephalaspideans
include both herbivorous and carnivorous species
(Kohn, 1983; Wägele & Klussmann-Kolb, 2005;
Malaquias et al., 2009b).
CHARACTERISATION OF THE STOMACH AND INTESTINE OF THE OPISTHOBRANCH Bulla Striata
Dietary specialization and the related modifications
of the digestive system were considered fundamental
aspects in opisthobranch evolution (Thompson,
1976; Mikkelsen, 2002; Malaquias et al., 2009b),
but in spite of that the digestive systems of these
animals is not fully investigated yet. Some light
microscopy studies dedicated to the digestive system
of cephalaspideans were published many years ago
(Fretter, 1939; Rudman, 1971, 1972b, 1972c). The
radular teeth and gizzard plates of some species were
studied using SEM (Gosliner, 1994; Malaquias & Reid,
2008), whereas histochemistry and TEM were used to
investigate the digestive system only in a very limited
number of species. The digestive system of Aplysia
is fairly well studied, with several articles reporting
histochemical and ultrastructural aspects of its organs
(Taïeb & Vicente, 1999; Lobo-da-Cunha, 1999, 2000;
Taïeb, 2001; Lobo-da-Cunha, 2001, 2002; Loboda-Cunha & Batista-Pinto, 2003, 2005, 2007). The
salivary glands and the oesophagus of the herbivorous
cephalaspidean Bulla striata have already been studied
with histochemical and ultrastructural methods (Loboda-Cunha & Calado, 2008; Lobo-da-Cunha et al.,
2010a, 2010b), but the digestive system of carnivorous
cephalaspideans has just started to be investigated
with the same level of detail (Lobo-da-Cunha et al.,
2009). To our best knowledge, the digestive systems of
umbraculoideans and pteropods were never studied by
TEM, and in runcinaceans only the digestive gland was
studied at the ultrastructural level (Kress et al., 1994).
In order to obtain more data for a comparative
analysis of the digestive system in opisthobranchs, the
stomach and intestine of B. striata were studied with
light and electron microscopy methods.
Specimens of Bulla striata Bruguière, 1792 about
2-3 cm in length were collected in Ria de Alvor
and Ria de Faro, two estuaries in the South coast of
Portugal. Stomach and intestine samples collected
from 5 animals were processed for light and electron
microscopy as reported below.
Morphology
For light microscopy, tissue pieces containing the
stomach, initial portion of the intestine and part of the
digestive gland were fixed for 24 h in Bouin solution,
dehydrated in increasing concentrations of ethanol and
embedded in paraffin. Middle and terminal segments
of the intestine were processed in the same way. Tissue
sections were stained with haematoxylin and eosin.
For transmission electron microscopy (TEM), samples
of stomach and intestine were fixed for about 2 h at
4°C in 2.5% glutaraldehyde and 4% formaldehyde
(obtained from hydrolysis of para-formaldehyde),
diluted with 0.4 M cacodylate buffer pH 7.4 (final
buffer concentration 0.28 M). After washing in buffer,
samples were postfixed with 2% OsO4 buffered with
cacodylate, dehydrated in increasing concentrations of
ethanol and embedded in Epon. Semithin sections (2
μm) for light microscopy were stained with methylene
blue and azure II. Ultrathin sections were stained with
uranyl acetate and lead citrate, before being observed
in a JEOL 100CXII transmission electron microscope
operated at 60 kV.
Histochemistry
The tetrazonium coupling reaction for protein
detection was applied to 2 μm sections of Epon
embedded stomach and intestine fragments. These
semithin sections were treated with a 0.6% solution
of H2O2 for 10 min., to remove the osmium tetroxide
fixative from the tissue. After washing in water, sections
were treated for 10 min with a freshly-prepared 0.2%
solution of fast blue salt B in veronal-acetate buffer
pH 9.2, washed in water and treated for 15 min with
a saturated solution of β-naphthol in veronal-acetate
buffer pH 9.2 (Ganter & Jollès, 1970). The PAS reaction
for polysaccharide detection was applied to sections of
paraffin embedded pieces and to semithin sections of
Epon embedded fragments. After oxidation with 1%
periodic acid for 10 min, tissue sections were washed
with water and stained with Schiff reagent for about 15
min (Ganter & Jollès, 1970). Alcian blue staining was
applied to sections of paraffin embedded material. For
63
Figure 2:
Histology and histochemistry of the stomach of B. striata. A. Transverse section through the middle of the U-shaped stomach (st) showing the
typhlosole (arrows). Numerous PAS positive secretory cells (arrowheads) can be seen in the stomach epithelium, but not in the long digestive gland
duct (ld). Digestive gland tissue (dg) surround the stomach. B. A few PAS positive secretory cells (arrowheads) can be seen in the epithelium of
the long digestive gland duct (ld) at the connection point with the stomach (st). C. Detail of the stomach epithelium showing lining epithelial cells
(asterisk) and PAS positive bottle-shape secretory cells (arrows). The unstained zone (arrowhead) in the basal region of these mucus-secreting cells
corresponds to the nucleus. D. Alcian blue stains stomach mucus-secreting cells (arrows) that are also present in the typhlosole (ts). E. Stomach
mucus-secreting cells (arrowheads) are not significantly stained by the tetrazonium coupling reaction, but this technique revealed protein-rich
secretory material at the apex of another type of secretory cells (arrow). nu - nuclei. F. Apical secretory material is not stained by PAS reaction
(arrow), but glycogen deposits in neighbour cells are strongly PAS positive (arrowhead).
detection of carboxylated polysaccharides, sections
were stained for 20 min. with 0.5% alcian blue in 3%
acetic acid (pH 2.5). To demonstrate the presence
of sulphated polysaccharides, sections were stained
for 20 min. with 0.5% alcian blue diluted in a HCl
solution with pH 1.0 (Ganter & Jollès, 1970). Sections
of paraffin embedded tissues were subsequently
stained with haematoxylin, washed, dehydrated and
mounted with DPX. Epon sections were washed, air
dried and mounted with DPX.
64
Cytochemistry
For polysaccharide detection by TEM, ultrathin
sections collected on copper grids were treated with a
5% solution of tannic acid for 10 min, briefly washed
in water, stained with 2% uranyl acetate for 10 min
and finally washed in water (Sannes et al., 1978).
For localization of acidic polysaccharides by
TEM, the colloidal iron method described by Knight
Figure 3:
Histology and histochemistry of the intestine of B. striata. A. Transverse section of the intestine (in) on the edge of the digestive gland (dg).
Haematoxylin and eosin stain. B. Semithin section of the intestine showing a granular cell (arrow) and epithelial cells with cilia (arrowhead) and
without cilia (asterisk). mu - muscular layer; nu - nuclei. C. The secretory material of granular cells is PAS positive (arrows), and positive reaction
is also detected in the basal region of a mucus-secreting cell (asterisk). nu - nucleus. D. The tetrazonium coupling reaction reveals protein-rich
secretion in the granular cells (arrows) and in mucus-secreting cells (asterisk). E. Semithin section of the intestine showing a PAS positive mucussecreting cell (arrowhead) and unstained ones (arrows). F. Intestine section stained with alcian blue and PAS reaction. Some mucus-secreting cells
are stained only by alcian blue (arrows), but the dark blue ones are stained by both procedures (arrowheads).
and Lewis (1992) was used. A stock solution of
colloidal iron was prepared adding 1 ml of a 25%
FeCl3 solution drop-by-drop to 50 ml of boiling water.
The dark red stock solution was filtered and dialysed.
Just before use, 1.5 ml of stock solution were diluted
with 7.5 ml of an acetic acid solution with a pH about
1.8. Ultrathin sections were collected on gold grids
and stained for 5 min with the diluted colloidal iron
solution. The grids were washed in 10% acetic acid
and finally in distilled water, before being observed
with the transmission electron microscope.
RESULTS
Anatomy, histology and histochemistry
The stomach of B. striata is embedded in a
narrow tip of the digestive gland (Fig. 1A). On the
surface of the digestive gland it is possible to see one
long straight duct that opens into the stomach near
the connection point between the stomach and the
posterior oesophagus (Fig. 1A). In order to disclose
what lies underneath the surface of the digestive
65
Figure 4:
Ultrastructural aspects of stomach and intestine lining epithelium. A. Stomach epithelial cells with a boarder of cilia (arrowheads) and microvilli
(asterisk). Mitochondria (arrows) are abundant in the apical region of these cells. B. Multivesicular body (arrow) close to the base of the microvilli
(asterisk) in an intestinal epithelial cell. C. Electron-dense lysosome-like bodies (ly) in the supranuclear region of an intestinal epithelial cell. A
Golgi stack can be seen in one of the cells (arrow). D. Basal region of stomach epithelium showing large and small patches of cytoplasm filled with
glycogen granules stained by the tannic acid-uranyl acetate method (arrows).
The secretory vesicles of a mucous cell are also stained (asterisks). ct - connective tissue.
gland, a 3D model was created from a series of
200 histological sections stained with haematoxylin
and eosin. To obtain an unobstructed view of the
stomach and its connections with the posterior
oesophagus, digestive gland ducts and intestine,
the digestive gland tissue was excluded from the
model (Fig. 1B-D). In the model it is possible to see
a short digestive gland duct that opens into the top
of the stomach, behind the terminal portion of the
posterior oesophagus (Fig, 1 C-D). In the animal,
this short digestive gland duct is completely covered
by digestive gland tissue being invisible on the
surface. The U-shaped stomach is just a segment of
the digestive tube without any external distinction
from the anterior portion of the intestine that circles
66
around the tip of the digestive gland, being visible at
its margin (Fig 1A-D). In the largest animals used in
this study, the intestine was about 2 cm long.
Two sections of the U-shaped stomach can be seen
when this organ is transversely cut (Fig. 2A). The
stomach wall forms a typhlosole along the inner curve
of this U-shaped organ, and a very large number of
secretory cells are present in the stomach epithelium
(Fig. 2A). On the other hand, secretory cells are rare
in the epithelium of digestive gland ducts (Fig. 2A-B).
The lining epithelium of the stomach is formed
by thin ciliated and non-ciliated columnar cells
interspersed with two types of secretory cells. Bottleshaped mucus-secreting cells are very abundant, with
a thin apical neck and a larger basal region containing
the nucleus (Fig. 2C-E). Much less frequent are the
cells with an apical mass of secretion (Fig. 2E-F). The
histochemical properties of both cell types can be
seen in Table 1. A thin muscular layer surrounds the
stomach epithelium.
In the intestine the typhlosole is absent (Fig. 3A).
This structure ends not far after the middle of the
digestive tube segment that goes from the curve of the
U-shaped stomach to the first curve of the intestine
around the tip of the digestive gland (Fig. 1C). Most
intestine epithelial cells possess cilia, but some are
non-ciliated (Fig. 3B). The most abundant secretory
cells present in the intestine are the granular cells
and mucus-secreting cells. The granular cells are
thinner and contain a large number of small secretory
granules most of them in the cytoplasm above the
nucleus, which is positioned approximately in the
centre of the cell (Fig. 3B-D). The histochemical
properties of this cell type are included in Table 1.
Mucus-secreting cells of the intestine are bottleshaped (Fig. 3C-E), but the histochemical techniques
show that two kinds of mucus secreting cells are
present in the intestine (Table 1). In sections stained
by both PAS reaction and alcian blue, it can be seen
that the larger mucus-secreting cells (mucous cells II,
in Table 1) are stained by alcian blue showing a light
blue colour. The thinner ones (mucous cells I, in Table
1) are stained by both procedures appearing with a
dark blue coloration in result of the superposition
of light blue and the magenta colour of PAS positive
cells, but none are stained by PAS reaction alone
(Fig. 3F). However, the change in the staining pattern
of mucus-secreting cells occurs gradually at the
transition zone between the stomach and the intestine.
After the end of the typhlosole the number of PAS
positive cells gradually diminishes in the digestive
tube, and after the first curve of the intestine only
about one third of the mucus-secreting cells are PAS
positive (Fig. 3E). In addition to these cell types, the
cells with an apical mass of protein-rich secretory
material found in the stomach epithelium are also
present along the intestine in small amounts (Table
1). A thin layer of muscular cells surrounds the
epithelium of the intestine (Fig. 3B).
Ultrastructure and cytochemistry
The lining epithelium is identical in both the
stomach and the intestine. It is formed by thin elongated
cells with a border of microvilli between 2 and 3 μm
long, and most of them also have cilia (Fig. 4A).
Vesicles, multivesicular bodies, some lysosome-like
bodies and several mitochondria can be seen in the
supranuclear region (Fig. 4A-C). A few lipid droplets
can be found in these epithelial cells, but glycogen is
the main reserve substance filling a substantial part of
the cytoplasm in some cells (Fig. 4D).
The mucus-secreting cells of the stomach are
filled with a large number of secretory vesicles of
variable dimensions with low or median electrondensity. They can be oval or irregular in shape
(Fig. 5A) and some of them may be fused forming
larger compartments with secretory material. The
vesicles contain very fine filaments forming a
reticulate pattern that can be denser in some vesicles
than in others (Fig. 5B). The secretory vesicles are
moderately stained by tannic acid-uranyl acetate
method for polysaccharide detection (Fig. 4D), and
with the colloidal iron method for acid polysaccharide
detection iron particles are distributed over the
secretory material contained in the vesicles (Fig.
5C). These cells possess several Golgi stacks formed
by a large number of flat cisternae, mainly located
around the nucleus (Fig. 5A-B). A few mitochondria
and rough endoplasmic reticulum cisternae are also
present. Very frequently, an intraepithelial nerve
terminal was seen in direct contact with the basal
region of a mucus-secreting cell. In ultrathin sections
of these zones the basal lamina has a reticulated
appearance, and some perforations are clearly visible
in the basal lamina (Fig. 5D).
In the intestine, the mucous cells I are similar
to the mucous cells of the stomach. However, the
majority of intestinal mucous cells (type II) possess
67
Figure 5:
Ultrastructure of stomach mucous cells. A. General view of the dilated basal region showing the nucleus (nu), a large number of secretory vesicles
(asterisks) and some Golgi stacks (arrows). B. The Golgi stacks (Gs) are formed by many flat cisternae, and the secretory material creates a
fine reticular pattern within the vesicles (asterisk). C. Colloidal iron particles attach to the secretory material within the vesicles (asterisks). D.
Intraepithelial nerve terminal (nt) attached to the base of a mucous cell (asterisk). In this region the basal lamina (bl) has a reticulated appearance
and is perforated (arrow). ct - connective tissue.
large electron-lucent vesicles in which the secretory
material forms a web of fine filaments linking small
cores with low electron-density (Fig. 6A). These
vesicles also fuse with each other, but the substances
they enclose are not significantly stained by the tannic
acid-uranyl acetate method. On the other hand, the
68
secretory material is strongly marked by colloidal iron
particles. Very fine strings of iron particles cover the
thin web of filaments and a high concentration of iron
particles is seen around the cores of secretory material
(Fig. 6B). The concentration of iron particles on these
cores creates a pattern with coarse spots, which is
Figure 6:
Ultrastructure of intestinal secretory cells A. Intestinal mucous cell containing secretory vesicles with a web of very fine filaments (arrowheads)
connecting small cores of secretory material (arrows). nu - nucleus. B. In the secretory vesicles, colloidal iron particles attach to the thin web of
filaments (arrowheads) and around the cores of secretory material (arrows). C. Cell containing an apical mass of secretory material (asterisks)
showing some microvilli at the apex (arrowhead). The secretory material of the granular cells has a higher electron density (arrows). D. Apical
region of a granular cell showing microvilli (asterisk), multivesicular bodies (arrows), and many electron-dense secretory vesicles (arrowheads).
very different from the more uniform distribution of
iron particles in the secretory vesicles of the stomach
type of mucous cells. The secretory vesicles fill the
cytoplasm almost completely and usually just some
Golgi stacks can be seen in peripheral zones of the
cytoplasm. These Golgi stacks formed by many
flattened cisternae resemble the ones observed in the
stomach mucus-secreting cells.
Cells with an apical mass of secretory material
were observed in ultrathin sections of both stomach
and intestine epithelia. These cells possess some
69
Table 1:
Histochemical properties of stomach and intestine secretory cells in Bula striata and Aplysia depilans.
PAS
reaction
Cells with apical
mass of secretion
Alcian blue Tetrazonium
pH 2.5
reaction
PAS
reaction
Bulla striata - Stomach
Cell types
Mucous cells
Alcian blue
pH 1.0
++
++
++
-
-
-
-
++
++
++
++
++
Cell type not observed
Aplysia depilans - Intestine
Mucous cells I
+
++
++
±/+
Mucous cells II
-/±
++
++
±/+
-
-
-
++
++
-
-
++
++
Granular cells
Alcian blue Tetrazonium
pH 2.5
reaction
Aplysia depilans - Stomach
Bulla striata - Intestine
Cells with apical
mass of secretion
Alcian blue
pH 1
++
++
++
Cell type not observed
++
-
-
++
- negative reaction; -/± negative or weak reaction; ±/+ weak or moderate reaction; + moderate reaction; ++ strong reaction
microvilli and their apical region is typically filled by
a membrane bound mass of secretory material with
a very irregular shape and median electron-density,
that seems to result from the fusion of smaller vesicles
(Fig. 6C). Material with identical electron-density and
texture is also present in round vesicles and Golgi stack
cisternae. Several small Golgi stacks and many rough
endoplasmic reticulum cisternae are present in these
cells that also contain a few lysosome-like bodies.
The intestinal granular cells are characterised
by a large number of spherical secretory vesicles
containing electron-dense material. These vesicles
are very abundant in the cytoplasm above the nucleus,
reach a diameter about 0.8 μm and never fuse with each
other (Fig. 6D). The cell apex is covered by microvilli
about 2 μm long. Some multivesicular bodies and
small electron-lucent vesicles are usually present in
the apical region, but endoplasmic reticulum cisternae
are not abundant (Fig. 6D). The nucleus is located in
the central part of the cell. Below the nucleus only
a small number of secretory vesicles are present,
because the basal region of these cells is filled with
very deep cell membrane invaginations associated
with a large number of mitochondria.
70
As in the stomach, intraepithelial nerve terminals
attached to the basal region of secretory cells and a
reticulated basal lamina with perforations were also
observed in the intestine of B. striata.
DISCUSSION
Cephalaspideans and Anaspideans are two
opisthobranch clades with a close phylogenetic
relationship (Dinapoli & Klussmann-Kolb, 2010;
Jörger et al., 2010), including the herbivorous
species B. striata and Aplysia depilans, respectively.
With the existing anatomical, histochemical and
ultrastructural data, it is now possible to make a
more detailed comparative analysis of the digestive
system of these two species. Both possess long
ribbon-shaped salivary glands, starting from the
posterior part of the buccal mass and ending
near the gizzard. Moreover, histochemical and
ultrastructural studies revealed that the salivary
glands of these species have in common two
types of mucus-secreting cells, named granular
mucocytes and vacuolated mucocytes. Nevertheless,
the ciliated cells present in the salivary glands
of these species are different, being secretory
in A. depilans and non-secretory in B. striata
(Lobo-da-Cunha, 2001, 2002; Lobo-da-Cunha &
Calado, 2008). Few mucous cells were found in
the oesophagus and crop of A. depilans while in
B. striata mucous cells are very abundant in the
anterior and posterior oesophagus (Lobo-da-Cunha
& Batista-Pinto, 2005; Lobo-da-Cunha et al. 2010a,
2010b). Both species have a gizzard, although with
a different number of hard plates. In A. depilans,
a filter chamber is positioned between the gizzard
and the stomach, containing many acicular teeth
to prevent the entrance of larger algal fragments
into the stomach (Howells, 1942; Fretter & Ko,
1979). In B. striata, the gizzard is followed by the
posterior oesophagus, but some acicular teeth are
present in the most anterior region of the posterior
oesophagus (Lobo-da-Cunha et al. 2010b).
In both species the stomach is embedded in the
digestive gland and linked to it by ducts, and the
intestine is attached to the digestive gland for most
of its length. Nevertheless, substantial anatomical
differences can be found in the stomach, which in
Aplysiidae ends in a caecum that does not exist in B.
striata (Howells, 1942; Fretter & Ko, 1979). A caecum
is also present in the stomach of the Thecosomata,
which are closely related with the Anaspideans
(Klussmann-Kolb & Dinapoli, 2006).
Mucus-secreting cells are very abundant in
the stomach epithelium of these opisthobranchs.
However, the secretory material of these cells is rich
in proteins in A. depilans (Lobo-da-Cunha & BatistaPinto, 2003) and that is not true for the stomach of
B. striata (Table 1). Despite that, in each of these
species stomach mucous cells form secretory vesicles
with low or medium electron-density containing
thin filaments of secretory material (Lobo-daCunha & Batista-Pinto, 2003). In addition to these
mucus-secreting cells, the stomach epithelium
of B. striata contains cells specialised in protein
secretion, whereas in the stomach of Aplysia just the
mucous cells have been reported so far (Howells,
1942; Lobo-da-Cunha & Batista-Pinto, 2003). In the
stomach of the carnivorous cephalaspideans Philine
aperta and Scaphander lignarius just one type of
mucus-secreting cells has been reported (Fretter,
1939). However, the carnivorous cephalaspidean
Melanochlamys cylindrica and the herbivore Bulla
quoyi seem to be devoid of secretory cells in the
stomach (Rudman, 1971, 1972c). On the other
hand, the stomach epithelium of Haminoea is more
complex, containing additional types of secretory
cells (Fretter, 1939; Rudman, 1971). The stomach
epithelium of the herbivore Haminoea hydatis
includes a cell type characterized by an apical
accumulation of secretory material (Fretter, 1939),
that could be related to the cells found in the stomach
and intestine of B. striata also containing a mass of
secretory material in the apical region. Among the
Acteonidae, secretory cells of the mucous type were
reported in the stomach of some species, but not in
others (Fretter, 1939; Rudman, 1972a).
Mucus-secreting cells are allegedly responsible for
the lubrication of the luminal surface of the digestive
tube and were also found in the stomach of many
other gastropods (Bolognani Fantin et al., 1982;
Roldan & Garcia-Corrales, 1988; Soto et al., 1990;
Leal-Zanchet, 1998). However, only a few papers
reported ultrastructure aspects of the stomach cells of
gastropods (Pipe, 1986; Triebskorn, 1989; Boer & Kits,
1990; Leal-Zanchet, 2002; Lobo-da-Cunha & Batista
Pinto, 2003; Martin et al., 2010).
In the intestine, A. depilans and B. striata contain
granular cells and mucus-secreting cells (Table 1).
The former are characterized by the presence of
electron-dense secretory vesicles containing proteins
and neutral polysaccharides, and could be classified
as serous cells (Lobo-da-Cunha & Batista-Pinto,
2007). In the intestine of B. striata, the extensive
system of cell membrane invaginations associated to
a large number of mitochondria in the basal region of
the granular cells suggests an intense active transport
in these cells. In the intestine of A. depilans just one
kind of mucous cells was detected (Lobo-da-Cunha &
Batista-Pinto, 2007), while in B. striata some are PAS
71
positive and others PAS negative (Table 1). In addition
to this difference in PAS reactivity, the mucous cells
of B. striata intestine can be distinguished by the
content of the secretory vesicles and by the pattern
of colloidal iron staining. They may represent two
sub-types of mucous cells or different stages of cell
maturation. The secretory vesicles containing a web
of thin filaments linking small cores of secretory
material in the intestinal type of B. striata mucous cell
resemble the vesicles described in mucus-secreting
cells of the anterior oesophagus of this species (Loboda-Cunha et al., 2010a).
The cells with an apical mass of secretion
observed in the stomach and intestine of B. striata
were not reported in Aplysia. These cells belong to a
different type, and can easily be distinguished from
the granular cells by the difference in electrondensity of the secretory material, absence of PAS
staining and fusion of secretory vesicles creating
the large mass of secretory material in the cell
apex, an aspect never observed in the granular cells
of both species (Lobo-da-Cunha & Batista-Pinto,
2007).
Two types of secretory cells were also reported
in the intestine of the opisthobranchs A. punctata
(Howells, 1942), B. quoyi (Rudman, 1971), S.
lignarius (Fretter, 1939) and in some species of Philine
(Fretter, 1939; Rudman, 1972b), but although their
characterization was based only on light microscopic
observations, those cells seem to correspond to the
intestinal mucous and granular cells of B. striata
and A. depilans (Lobo-da-Cunha & Batista-Pinto,
2007). However, in Haminoea zelandiae just one
type of secretory cell was reported in the intestine
(Rudman, 1971). Ultrastructural observations of
the intestinal epithelium of the marine snail Nerita
picea revealed secretory cells very similar to the
granular cells of B. striata and A. depilans (Pfeiffer,
1992). In the limpet Patella vulgata, the intestinal
epithelium contains club-shaped protein secreting
cells rich in rough endoplasmic reticulum cisternae
and its secretion coats the fecal rods with a protein
72
layer, preventing them from disintegrating (Bush,
1988). These cells are also similar to the granular
cells of B. striata and A. depilans, which may have
similar functions, but the secretory granules in P.
vulgata club-shaped cells are not stained by PAS
reaction. However, considering the data that support
an absorptive function for the intestine, secretion of
digestive enzymes cannot be ruled out for intestinal
cells containing proteins in their secretory vesicles.
Two or more secretory cell types were encountered
in the intestine of pulmonate gastropods, including
mucous cells and other secretory cells (Triebskorn,
1989; Boer & Kits, 1990; Franchini & Ottaviani,
1992; Leal-Zanchet, 1998, 2002).
The presence of many intraepithelial nerve
terminals in close association with the base of
secretory cells in both stomach and intestine of B.
striata put in evidence the importance of nervous
control over the activity of these parts of the digestive
tract, as previously reported in other species of
gastropods (Bush, 1988; Boer & Kits, 1990; Lobo-daCunha & Batista-Pinto, 2003).
The columnar cells of the stomach and intestine
lining epithelium are also identical in B. striata and
A. depilans. Lysosomes with arilsulphatase activity
are very conspicuous in the supra-nuclear region
of stomach and intestine columnar epithelial cells
of A. depilans and probably are responsible for
the intracellular digestion of substances collected
from the lumen by endocytosis (Lobo-da-Cunha &
Batista-Pinto, 2003, 2007). The digestive gland is
recognized as the main sites of digestion and nutrient
absorption in gastropods, but it was demonstrated
that absorption of nutrients occurs along the digestive
tract (Walker, 1972; Orive et al., 1979). According to
some authors, the function of the gastropod intestine
is the consolidation of fecal pellets (Mikkelsen,
1996). However, the presence of a microvillous
border, lysosomes and the accumulation of lipids and
glycogen in epithelial cells of the digestive tract of
gastropods were considered as signs of an absorptive
function (Roldan & Garcia-Corrales, 1988; Boer &
Kits, 1990). In addition, the observation of vesicles
and multivesicular bodies that are usually related
with endosomes in the apical region of epithelial
cells strongly supports the existence of an endocytic
activity in the stomach and intestine of B. striata.
The thin muscular layer in the intestine wall of B.
striata suggests that ciliary action is an important
factor for the movement of fecal matter. A partial
typhlosole extending a short distance into the
intestine was considered the plesiomorphic state
in cephalaspideans, but its absence in the intestine
of Bulla and other euopisthobranch genera was
previously reported (Mikkelsen, 1996).
To conclude, the available data show that
despite some differences the digestive systems of
A. depilans and B. striata present several similar
anatomical aspects and many of their cell types
are identical. It will be interesting to see if some
characters of the digestive system such as cell types
are phylogenetically relevant or related with dietary
specialization. However, for a cladistic analysis it
will be necessary to have detailed ultrastructural
and histochemical information on digestive system
cells of more species. Additionally, the diversity of
cell types, especially in the intestine of B. striata,
suggest the secretion of different specific substances
that would be interesting to study further in order to
improve our knowledge about the physiology of the
digestive process in opisthobranchs. The application
of histochemical methods in semithin sections and
the ultrastructural study have proved to be very
valuable for the detection and characterization of
those cell types, allowing a better understanding of
the digestive system in opisthobranchs.
ACKNOWLEDGEMENTS
The authors thank Mr João Carvalheiro and
Ms Joana Carvalheiro for reproduction of the
photomicrographs. Rita Coelho holds a grant from the
“Fundação para a Ciência e a Tecnologia”, Portugal
(BDE 15577/2005). This work was supported by
ICBAS and CIIMAR.
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Thalassas, 27 (2): 77-100
ADDITIONS TO THE INVENTORY
OF Mollusca opisthobranchia OF GALICIA
(NW IBERIAN PENINSULA)
URGORRI, V.(1), DÍAZ-AGRAS, G.(1), BESTEIRO, C.(1) & MONTOTO, G.(1)
Key words: Opisthobranchia, new records, Galicia, NW Iberian Peninsula, taxonomy, distribution, habitat, Nudibranchia,
Cephalaspidea, Anaspidea, Acochlidiomorpha, Sacoglossa.
ABSTRACT
INTRODUCTION
A total of 36 species of Mollusca Opisthobranchia
collected on Galician coasts (NW Iberian Peninsula)
are presented in this article: one Cephalaspidea, one
Anaspidea, two Acochlidiomorpha, two Sacoglossa
and 30 Nudibranchia. Of these, 15 had not been
previously quoted for Galicia; the other 21, despite
being previously quoted, represent rare species or
species little known on these coasts. For each species,
remarks are made concerning different taxonomic
aspects, their distribution and habitat characteristics.
The littoral bottoms of the coasts of Galicia
present a high diversity of habitats and species as
a consequence of several physical and ecological
factors; they stretch as far as 1500 km of coast line,
very irregularly, with open environments exposed
to the beating of the ocean and more protected
‘rías’ with varied dimensions and orography. Their
waters, as a consequence of the phenomenon of
coastal upwelling, present a great phytoplanctonic
richness and are subsequently responsible for the
high secondary production, capable of keeping a high
biodiversity of species of marine animals.
(1) Estación de Bioloxía Mariña da Graña,
In the littoral fauna of Galicia, Gasteropoda
Mollusca represent an important share, and of these,
testacea species are very well-known (Hidalgo,
1886; Cadée, 1968; Hernández-Otero & JiménezMillán, 1972; Rolán, 1983; Otero-Schmitt & Trigo,
Universidade de Santiago de Compostela, Casa do Hórreo,
Rúa da Ribeira 1,
15590, A Graña (Ferrol), Spain.
77
URGORRI, V., DÍAZ-AGRAS, G., BESTEIRO, C. & MONTOTO, G.
Figure 1:
Location maps of the localities where the species quoted in this article were collected.
78
ADDITIONS TO THE INVENTORY OF Mollusca opisthobranchia OF GALICIA
1986, 1987, 1989; Trigo & Otero-Schmitt, 1987;
Troncoso et al., 1988, 1990; Rolán et al., 1989;
Troncoso & Urgorri, 1990, 1991; Olabarria, Urgorri
& Troncoso, 1997a, 1997b; Olabarria, Troncoso
& Urgorri, 1997; Carmona-Zalvide & Urgorri,
1999a, 1999b; amongst others). However, there
is not such exhaustive knowledge of Gastropoda
Opisthobranchia, above all, of those lacking in shell
in their adult stage. Of the Opisthobranchia that
still keep their shell more or less reduced, there are
some mentions in Galicia from the middle of the 19 th
century (MacAndrew, 1849, 1850; MacAndrew &
Woodward, 1864; Hidalgo, 1886, 1917; Cadée, 1968;
Hernández-Otero & Jiménez-Millán, 1972; amongst
others). But of the Opisthobranchia lacking in shell,
it is not until the last quarter of the 20th century when
the first quotes come out (Ros, 1975; Ortea, 1977a;
Ortea & Urgorri, 1978; Polo et al., 1979; Ortea
& Urgorri, 1979a, 1979b; Urgorri, 1981; Ortea &
Urgorri, 1981a, 1981b; amongst others).
When the inventory of Opisthobranchia from
Galicia was published, Urgorri & Besteiro (1983)
compiled all the previous information, adding
numerous quotes unpublished until then. In subsequent
years, new quotes were added to the inventory by
different authors (Rolán, 1983; Cobo, 1985; Urgorri
& Besteiro, 1986; Rolán-Álvarez & Rolán, 1989;
Rolán, Otero & Rolán-Álvarez, 1989; García, Urgorri
& López-González, 1990; Rolán, Rolán-Álvarez
& Ortea, 1991; Urgorri, Cobo & Besteiro, 1991;
Calado & Urgorri, 2002; amongst others). Apart
from these contributions, after almost 30 years
since the publication of the inventory of Galicia
(Urgorri & Besteiro, 1983), numerous specimens of
Opisthobranchia have been collected on our coasts,
presenting in this article those additions that are
considered to be the most noteworthy, not only for
their novelty, but also for their oddities or shortage of
mentions and those that presented any confusion and
needed to be clarified or specified. They make up a total
of 36 species of Mollusca Opisthobranchia of Galicia: a
Cephalaspidea, an Anaspidea, two Acochlidiomorpha,
two Sacoglossa and 30 Nudibranchia.
On the other hand, the zoological systematic,
so accustomed in the recent past to the traditional
classification, is currently living a revolution in all
taxonomic levels, basically stimulated by molecular
sequence data. This booster has made the world of
zoology go more deeply into the phylogenetic analyses
based on morphological and molecular data, which has
undoubtedly caused a magnificent scientific boost.
Nevertheless, the extent of zoology and the great
animal diversity determines that the results of the
phylogenetic analyses have not evolved sufficiently in
any direction yet, being still provisional in many cases,
despite moving forward progressively. Therefore,
different authors and articles have produced year after
year results that in some cases are opposing or at least
not concordant. Following one or another systematic
ordering is sometimes circumstantial and the one
chosen may be left behind the times in a short period
of time to a greater or lesser extent. Consequently, as
we agree with the arguments used by Cervera et al.
(2004) for the ordering followed in his article, it has
been decided to use the same systematic ordering as
that used in this checklist of Opisthobranchs from
Spain and Portugal.
STUDY AREA
Urgorri & Besteiro (1983) decided to include
the quotes of the littoral system and the bathyal
zone of our coasts in the Inventory of the Mollusca
Opisthobranchia of Galicia. In this article, in which
new additions to that inventory are given, the
quotes included are confined to the littoral system,
as the species of Opisthobranchia collected in
the deep-sea (bathyal and abyssal zones), are still
under study.
All quotes presented correspond to species
sampled on the whole littoral of Galicia, although
most localities are confined to the ‘rías’ of Ferrol, A
Coruña, Arousa and Ares.
Below are listed the 81 mentioned localities, with
the place name and geographical coordinates of their
79
location, ordered from north to south following the
coast from Ribadeo to A Guarda. This list, which may
seem to be redundant, as localities are also written
up for each of the species, allows an overall view of
the localities correlated and shown on the maps of
figure 1.
1. Benquerencia (Lugo) - (43° 33’ 47” N; 007° 10’
42” W)
2. Burela (Lugo) - (43° 38’ 50” N; 007° 20’
35” W)
3. Sismundi (Ortigueira) - (43° 42’ 12” N; 007° 52’
31” W)
4. Capela do Porto, (Meirás, Valdoviño) - (43° 36’
53” N; 008° 11’ 45” W)
5. O Pieiro Pequeno (Ría de Ferrol) - (43° 26’ 54” N;
008° 20’ 40” W)
6. O Pieiro Pequeno (Ría de Ferrol) - (43° 27’ 29” N;
008° 20’ 14” W)
7. O Zorrón (Ría de Ferrol) - (43° 27’ 22” N; 008°
20’ 23” W)
8. Canelas (Ría de Ferrol) - (43° 28’ N; 008° 19’ W)
9. Canelas (Ría de Ferrol) - (43° 27’ 50” N; 008° 19’
44” W)
10. Viñas (Ría de Ferrol) - (43° 27’ 50” N; 008° 19’
47” W)
11. Barbeira (Ría de Ferrol) - (43° 28’ 08” N; 008°
19’ 07” W)
12. Cariño (Ría de Ferrol) - (43° 27’ 55” N; 008° 19’
17” W)
13. Fornelos (Ría de Ferrol) - (43° 28’ 02” N; 008°
18’ 49” W)
18’ 57” W)
18’ 48” W)
16. San Cristovo (Ría de Ferrol) - (43° 27’ 56” N; 008°
18’ 06” W)
17. Rabo da Porca (Ría de Ferrol) - (43° 27’ 37” N;
008° 17’ 53” W)
008° 18’ 15” W)
008° 17’ 50” W)
80
20. San Felipe (Ría de Ferrol) - (43° 27’ 47” N; 008°
18’ 57” W)
21. Castelo de San Felipe (Ría de Ferrol) - (43° 27’
46” N; 008° 16’ 50” W)
22. Leuseda (Ría de Ferrol) - (43° 27’ 54” N; 008°
16’ 30” W)
16’ 30” W)
16’ 38” W)
16’ 47” W)
26. O Pereiro (Ría de Ferrol) - (43° 27’ 58” N; 008°
16’ 18” W)
27. O Pereiro (Ría de Ferrol) - (43° 28’ 01” N; 008°
16’ 15” W)
28. O Vispón (Ría de Ferrol) - (43° 27’ 56” N; 008°
16’ 05” W)
29. A Graña (Ría de Ferrol) - (43° 28’ 53” N; 008°
15’ 26” W)
15’ 33” W)
15’ 35” W)
32. A Cabana (Ría de Ferrol) - (43° 29’ 12” N; 008°
15’ 29” W)
33. A Cabana (Ría de Ferrol) - (43° 29’ 10” N; 008°
15’ 29” W)
34. A Malata (Ría de Ferrol) - (43° 29’ 23” N; 008°
14’ 57” W)
35. Promontoiro - A Barca (Ría de Ferrol) - (43° 27’
46” N; 008° 13’ 54” W)
36. A Bestarruza (Ría de Ferrol) - (43° 27’ 49” N;
008° 15’ 42” W)
37. O Baño (Ría de Ferrol) - (43° 27’ 47” N; 008° 15’
57” W)
38. O Baño (Ría de Ferrol) - (43° 27’ 39” N; 008° 15’
59” W)
39. A Redonda (Ría de Ferrol) - (43° 27’ 46” N; 008°
16’ 10” W)
16’ 06” W)
16’ 15” W)
42. A Palma (Ría de Ferrol) - (43° 27’ 54” N; 008°
16’ 32” W)
43. Ría de Ferrol - (43° 28’ 10” N; 008° 14’ 47”
W)
44. Ría de Ferrol - (43° 28’ 15” N; 008° 15’ 09”
W)
45. Ría de Ferrol - (43° 28’ 20” N; 008° 15’ 02”
W)
46. Ría de Ferrol - (43° 28’ 10” N; 008° 12’ 43”
W)
47. Cu da Raiña (Ría de Ferrol) - (43° 27’ 27” N; 008°
17’ 35” W)
48. A Moa do Segaño (Ría de Ferrol) - (43° 27’ 25” N;
008° 18’ 42” W)
49. O Segaño (Ría de Ferrol) - (43° 27’ 03” N; 008°
19’ 12” W)
18’ 54” W)
18’ 56” W)
52. As Merloeiras (Ría de Ares) - (43° 26’ 24” N; 008°
19‘ 20” W)
53. Perbes (Ría de Ares) - (43° 22’ 50” N; 008° 13’
46” W)
54. San Amede (Ría de Ares) - (43° 23’ 23” N; 008°
16’ 15” W)
55. Ría de Ares (43° 22’ 57” N - 43° 25’ 18” N; 008°
13’ 29” W - 008° 17’ 32” W)
56. A Moreira (Ría da Coruña) - (43° 22’ 30” N; 008°
23’ 17” W)
57. O Grelle (Ría da Coruña) - (43° 22’ 53” N; 008°
23’ 30” W)
58. O Cabalo (Ría da Coruña) - (43° 23’ 05” N; 008°
23’ 26” W)
59. Punta Herminia (A Coruña) - (43° 23’ 25” N; 008°
24’ 02” W)
60. As Agudelas (A Coruña) - (43° 23’ 26” N; 008°
24’ 24” W)
61. O Boi (A Coruña) - (43° 23’ 19” N; 008° 24’ 54”
W)
62. Orzán (A Coruña) - (43° 22’ 42” N; 008° 24’ 36”
W)
63. O Basteo (A Coruña) - (43° 22’ 33” N; 008° 27’
19” W)
64. Aguiño (Ría de Arousa) - (42° 31’ 01” N; 009°
00’ 41” W)
65. Xidoiros (Ría de Arousa) - (42° 32’ 44” N; 008°
55’ 30” W)
66. Cambados (Ría de Arousa) - (43° 31’ 17” N; 008°
49’ 18” W)
67. Ansuíña de Micaela (Ría de Arousa) - (42° 30’
05” N; 008° 53’ 04” W)
68. Mesa do Con (Ría de Arousa) - (42° 31’ 30” N;
008° 54’ 59” W)
69. Canal do Grove (Ría de Arousa) - (42° 28’ 32” N;
008° 58’ 26” W)
70. Canal do Grove (Ría de Arousa) - (42° 27’ 50” N;
008° 58’ 14” W)
71. San Martiño do Grove (Ría de Arousa) - (42° 30’
59” N; 008° 53’ W)
03” N; 008° 52’ 04” W)
07” N; 008° 55’ 03” W)
59” N; 008° 53’ 57” W)
75. Rodel das Figueiras (Ría de Arousa) - (42° 28’ 30”
N; 008° 57’ 36” W)
76. San Vicente do Mar (O Grove) - (42° 27’ 10” N;
008° 55’ 25” W)
77. Ensenada da Lanzada (Ría de Pontevedra) - (42°
25’ 48” N; 008° 53’ 38” W)
78. Illa de Ons (Ría de Pontevedra) - (42° 23’ 12” N;
008° 55’ 05” W)
79. Alcabre (Ría de Vigo) - (42° 14’ 05” N; 008° 46’
08” W)
80. Continental Shelf of Galicia - (43° 34’ 07” N; 008°
36’ 32” W - 43° 34’ 41” N; 008° 35’ 35” W)
81. Continental Shelf of Galicia - (43° 32’ 02”
N; 008° 37’ 31” W - 43° 32’ 48” N; 008° 35’
59” W)
The quoted species were collected from 24/09/1976
to 19/11/2010; three quarters of them are posterior to
the publication of the inventory of Urgorri & Besteiro
(1983). The remaining fourth part corresponds to
species that have been mistakenly quoted or not
identified with certainty.
81
Figure 2:
A: Gastropteron rubrum (Rafinesque, 1814). B: Asperpina loricata (Swedmark, 1968). C: Microhedyle glandulifera
(Kowalevsky, 1901). D: Hermaea bifida (Montagu, 1815). E: Hermaeopsis variopicta (Costa, 1869).
F: Corambe testudinaria Fischer, 1889. G: Okenia aspersa (Alder & Hancock, 1845).
H: Trapania tartanella (Ihering, 1885).
82
RESULTS
Superorder OPISTHOBRANCHIA Milne-Edwards,
1848
Order CEPHALASPIDEA Mikkelsen, 1996
Family GASTROPTERIDAE Swainson, 1840
Gastropteron rubrum (Rafinesque, 1814)
Material: Continental Shelf of Galicia,
14/09/2003, (43° 34’ 07” N; 008° 36’ 32” W - 43°
34’ 41” N; 008° 35’ 35” W). 1 specimen 14 mm long
(fixed), collected on bottoms of muddy sand at a depth
of 149 m. Continental Shelf of Galicia, 25/09/2004,
(43° 32’ 02” N; 008° 37’ 31” W - 43° 32’ 48” N; 008°
35’ 59” W). 3 specimens, the largest measuring 14
mm long when fixed, collected on bottoms of muddy
sand at a depth of 151 m.
Distribution in Galicia: So far unknown on our
coasts, it is the first quote in Galicia.
Remarks: Cervera et al. (1988, 2004) mistakenly
mention the presence of Gastropteron rubrum in
both checklists in area 2 (Galicia, western Asturias
and northern Portugal) and attribute the quote to
Ros (1975 as G. meckeli), who had carried out only
two samplings in area 2 for this publication: an
infralittoral at Vilagarcía de Arousa and an intertidal
at Canido, where he did not collect this species. This
author (Ros, 1975) quotes it for the Catalan littoral
(area 8), collecting more than 100 specimens on trawl
fishing grounds of Blanes (ba1, ba2, ba3 & ba5), at a
depth from 40 to 250 m.
Order ANASPIDEA Fischer, 1883
Family APLYSIIDAE Lamarck, 1809
Aplysia fasciata Poiret, 1789
Material: Aguiño (Ría de Arousa), 16/10/2000,
(42° 31’ 01” N; 009° 00’ 41” W). 1 specimen 250 mm
long in tide pools of rocky intertidal.
Distribution in Galicia: This species had only
been mentioned by Rolán (1983) at Ría de Vigo.
Remarks: Of the three species known in Galicia,
A. fasciata is undoubtedly the only infrequent in
contrast to A. punctata and A. depilans, which are
very frequent and abundant at the whole Galician
littoral.
Order ACOCHLIDIOMORPHA Salvini-Plawen,
1983
Family HEDYLOPSIDAE Odhner, 1952
Asperpina loricata (Swedmark, 1968)
Material: Mesa do Con (Ría de Arousa),
05/05/1981, (42° 31’ 30” N; 008° 54’ 59” W). 9
specimens, the largest 1.2 mm long, collected on
bottoms of sand with shelly gravel and maërl at
a depth of 8.7 m. San Martiño do Grove (Ría de
Arousa), 17/02/1981, (42° 30’ 59” N; 008° 53’ 57”
W). 1 specimen, 1 mm long, on bottoms of sand with
maërl at a depth of 8.5 m.
Distribution in Galicia: This species was
quoted in Galicia by Cobo (1985) and Arnaud et
al. (1986).
Remarks: The quotes of Asperpina loricata and
other mesopsammic Opisthobranchia: Philinoglossa
helgolandica, Hedylopsis spiculifera and Microhedyle
glandulifera which Arnaud et al. (1986) mention
in ‘Galicia’ in an imprecise way, correspond to the
dissertation by Cobo (1984), as these authors point
out in the additional notes of their publication. A
wide summary of the results of the study of Cobo
(1984) were published in a small popular science book
(Cobo, 1985), where the situation of the sampling
localities, which has been included in this article, is
precisely mentioned.
Family MICROHEDYLIDAE Hertling, 1930
Microhedyle glandulifera (Kowalevsky, 1901)
Material: O Pereiro (Ría de Ferrol), 02/12/1986,
(43° 27’ 58” N; 008° 16’ 18” W). 195 specimens, the
largest 1.7 mm long, in Amphioxus sand at a depth
of 12 m. Leuseda (Ría de Ferrol), (43° 27’ 54” N;
008° 16’ 30” W), sand of Amphioxus at a depth of
83
Figure 3:
A: Trapania maculata Haefelfinger, 1960. B: Trapania pallida Kress, 1968. C: Thecacera pennigera (Montagu, 1815).
D: Crimora papillata Alder & Hancock, 1862. E: Hypselodoris cantabrica Bouchet & Ortea, 1980.
F: Chromodoris luteorosea (Rapp, 1827). G: Cadlina pellucida (Risso, 1826).
H: Discodoris stellifera (Vayssière, 1904).
84
13-18 m. 362 specimens: 21/03/1978, 08/04/1978,
20/10/1978, 18/11/1980. A Palma (Ría de Ferrol),
02/06/2004, (43° 27’ 54” N; 008° 16’ 32” W). 19
specimens 1 mm long, in Amphioxus sand at a depth
of 14 m. Rabo da Porca (Ría de Ferrol), 02/06/2004,
(43° 27’ 37” N; 008° 17’ 53” W). 8 specimens in
Amphioxus sand at a depth of 13 m. Fornelos (Ría
de Ferrol), 20/10/1978, (43° 27’ 51” N; 008° 18’
57” W). 34 specimens, the largest 1.3 mm long, in
Amphioxus sand at a depth of 18 m. Cariño (Ría de
Ferrol), 10/02/2004, (43° 27’ 55” N; 008° 19’ 17” W).
5 specimens, the largest 1.1 mm long, in Amphioxus
sand at a depth of 17 m. Canelas (Ría de Ferrol),
24/09/1983, (43° 28’ N; 008° 19’ W). 32 specimens
in shelly sand at a depth of 13 m. O Pieiro Pequeno
(Ría de Ferrol), 24/09/1983, (43° 26’ 54” N; 008°
20’ 40” W). 10 specimens in Amphioxus sand at a
depth of 25 m. Perbes (Ría de Ares), 02/04/1980,
(43° 22’ 50” N; 008° 13’ 46” W). 8 specimens in
sand at a depth of 9-10 m. Xidoiros (Ría de Arousa),
28/01/1980, (42° 32’ 44” N; 008° 55’ 30” W). 1
specimen in Amphioxus sand at a depth of 12 m.
San Martiño do Grove (Ría de Arousa), (42° 31’
07” N; 008° 55’ 03” W), in sand at a depth of 9 m.
262 specimens: 28/01/1980, 04/03/1981, 05/05/1981.
San Martiño do Grove (Ría de Arousa), 03/05/1981,
(42° 31’ 03” N; 008° 52’ 04” W). 73 specimens in
Amphioxus sand at a depth of 8 m. San Martiño do
Grove (Ría de Arousa), (42° 30’ 59” N; 008° 53’
W), sand with shelly gravel and maërl at a depth
of 8-9 m. 12 specimens: 17/02/1981, 06/07/1982.
Ansuiña de Micaela (Ría de Arousa), (42° 30’ 05”
N; 008° 53’ 04” W), Amphioxus sand with maërl
at a depth of 9 m. 178 specimens: 17/02/1981,
04/03/1981, 01/04/1981, 05/05/1981. Canal do Grove
(Ría de Arousa), 17/01/1978, (42° 28’ 32” N; 008°
58’ 26” W). 2 specimens in sand at a depth of 60 m.
Rodel das Figueiras (Ría de Arousa), (42° 28’ 30”
N; 008° 57’ 36” W), in Amphioxus sand at depths
of 47, 50 and 56 m. 56 specimens: 25/11/1980,
01/07/1981, 21/10/1981. Ensenada da Lanzada (Ría
de Pontevedra), 03/08/1982, (42° 25’ 48” N; 008°
53’ 38” W). 24 specimens in Amphioxus sand at a
depth of 10-20 m. Illa de Ons (Ría de Pontevedra),
09/04/1980, (42° 23’ 12” N; 008° 55’ 05” W). 14
specimens in Amphioxus sand at a depth of 35 m.
Alcabre (Ría de Vigo), 23/02/1981, (42° 14’ 05” N;
008° 46’ 08” W). 2 specimens in sand at a depth
of 28 m.
The size of all specimens quoted in the material
ranged from 0.5 to 3.5 mm long.
Distribution in Galicia: This species was quoted
in Galicia by Urgorri & Besteiro (1983, as Unela
odhneri), Cobo (1985) and Arnaud et al. (1986).
Remarks: As previously commented on Asperpina
loricata (vide supra), the quotes of Microhedyle
glandulifera that Arnaud et al. (1986) mention in
an imprecise way in ‘Galicia’, correspond to the
dissertation by Cobo (1984), as these authors point out
in the additional notes of their publication. Previously,
it had been mistakenly quoted by Urgorri & Besteiro
(1983) as Unela odhneri; the quotes of Cobo (1985)
and posterior recollections of the species are included
herein.
It is also important to emphasize that the followup of the fauna of Amphioxus sand at Ría de Ferrol
for many years, revealed that the populations of
Microhedyle glandulifera and other mesopsammic
Opisthobranchia have drastically decreased as a
consequence of the exponential increase of pollution
and the decrease of hydrodynamics due to the
closing of the ‘ría’ that the construction of the outer
port breakwater caused. This fact can be proved by
comparing the number of specimens and the dates
in the first four related localities. Unfortunately, the
value of mesopsammic Opisthobranchia is confirmed
once again as ecological indicators, a fact that had
already been stated by Poizat (1983), 25 years ago,
for the Gulf of Marseilles: “From the progressive
alteration of the ecological conditions (lowering
of marine hydrodynamism together with the rise
of the pollution impact) between 1969 and 1977,
in infralittoral and circalittoral zones of the gulf
of Marseilles, originated significant modifications
of the mesopsammic Opisthobranch population:
mainly generalised change in the frequency of the
species”.
85
Order SACOGLOSSA Von Ihering, 1876
Suborder PLAKOBRANCHACEA Rang, 1829
Family HERMAEIDAE Adams & Adams, 1854
Hermaea bifida (Montagu, 1815)
Material: Leuseda (Ría de Ferrol), 22/08/1996,
(43° 27’ 58” N; 008° 16’ 47” W). 1 specimen 5 mm
long, collected on a red algae at a depth of 5 m.
Distribution in Galicia: The only quote known
for this species in Galicia is that from Vigo (Rolán,
1983).
Remarks: Another 7 specimens of Hermaea
sp. are present, collected in the years 1977, 1978
and 1979 in other localities of Ría de Ferrol, which
presumably belong to this species, but whose correct
identification is still to be confirmed.
Hermaeopsis variopicta (Costa, 1869)
Material: O Pieiro Pequeno (Ría de Ferrol),
05/05/2007, (43° 27’ 29” N; 008° 20’ 14” W). 1
specimen 7 mm long, on red algae on rocky bottoms
at a depth of 10 m.
Distribution in Galicia: Only known from
Benquerencia (Lugo), (Ortea, 1977a, 1977b; Urgorri
& Besteiro, 1983) and from Ría de Vigo (RolánÁlvarez & Rolán, 1989).
Remarks: All quotes of this species on our
coasts (Ortea, 1977a, 1977b; Urgorri & Besteiro,
1983) correspond to an only specimen collected by
Ortea in Benquerencia (Lugo) and to the quote by
Rolán-Álvarez & Rolán (1989), in which neither the
number of specimens nor the locality at Ría de Vigo
are specified.
Order NUDIBRANCHIA Blainville, 1814
Suborder ANTHOBRANCHIA Minichev, 1970
Infraorder DORIDINA Pelseneer, 1894
Family CORAMBIDAE Bergh, 1871
Corambe testudinaria Fischer, 1889
Material: Sismundi (Ortigueira), 20/08/1984, (43°
86
42’ 12” N; 007° 52’ 31” W). 1 specimen collected
on the infralittoral of the interior area of Ría de
Ortigueira.
Distribution in Galicia: This species had been
previously quoted on our coasts by Urgorri (1981, as
Corambe sp.) and García, Urgorri & López-González
(1990), being the specimens from Galicia the same in
both publications.
Remarks: The present quote of C. testudinaria
represents the fourth Iberian locality where it was
found and extends its distribution in the Iberian
Peninsula to the north.
Family GONIODORIDIDAE Adams & Adams, 1854
Okenia aspersa (Alder & Hancock, 1845)
Material: Canelas (Ría de Ferrol), 24/06/1987,
(43° 27´ 50” N; 008° 19´ 44” W). 1 specimen 10 mm
long collected on infralittoral bottoms of Amphioxus
sand at a depth of 14 m.
Remarks: The species of the genus Okenia are
not very frequent in the Iberian Peninsula. No other
species of the genus had been recorded before from
the NW peninsular coasts, except for O. mediterranea
which was quoted in Vigo by Valdés & Ortea (1995).
Okenia aspersa, known from some localities of the
British Islands and adjacent coasts of Western Europe,
is one of the least quoted in the Iberian Peninsula,
only known for being mentioned by Cervera et al.
(1991) in Sagres (Portugal).
Trapania tartanella (Ihering, 1885)
Material: Viñas (Ría de Ferrol), 01/08/1996
(43° 27’ 50” N; 008° 19’ 47” W). 34 specimens, but
only 4 collected, the largest 14 mm long; they were
sampled on the sponge Desmacidon fructicosum
on rocky bottoms at a depth of 14 m. Fornelos
(Ría de Ferrol), (43° 28’ 02” N; 008° 18’ 49” W),
from 19 to 20.5 m deep on rocky bottoms on the
sponge Desmacidon fructicosum: 16/05/1991, 14
specimens, but only 2 collected, the largest 10
mm long; 02/08/1992, 22 specimens, the largest
13 mm long; 05/08/1996, 17 specimens, but only
3 collected, the largest 12 mm long; 17/08/1996,
1 specimen 9.5 mm long. Cu da Raiña (Ría de
Ferrol), 23/08/1992, (43° 27’ 27” N; 008° 17’ 35”
W). 3 specimens, the largest 19 mm long, collected
on a rock on the sponge Desmacidon fructicosum
on shelly gravel bottoms at a depth of 17 m. A
Redonda (Ría de Ferrol), 01/08/1992, (43° 27’ 51”
N; 008° 16’ 06” W). 3 specimens, the largest 21 mm
long, collected on a rock on the sponge Desmacidon
fructicosum at a depth of 14 m. O Boi (A Coruña),
19/09/2002, (43° 23’ 19” N; 008° 24’ 54” W). 12
specimens, the largest 15 mm long, grouped on
sponges on a rocky wall of a sand channel.
Distribution in Galicia: Quoted by Urgorri &
Besteiro (1983), by pers. comm. of Dr. B. Picton, in
several localities of the ‘rías’ of Arousa, Pontevedra
and Vigo.
Remarks: Trapania tartanella is a locally
abundant species in Galicia, provided it is located
in the specific habitat it lives in, on the sponge
Desmacidon fructicosum; this sponge is to be
found at Ría de Ferrol on infralittoral rocky areas,
preferably below the laminarian forest and as far as
the confluence of the rocky area with the sediment,
approximately from 17 to 25 m deep.
Trapania maculata Haefelfinger, 1960
Material: O Boi (A Coruña), 19/09/2002, (43°
23’ 19” N; 008° 24’ 54” W). 2 specimens, the largest
16 mm long, on sponges on a rocky wall of a sand
channel, at a depth of 18 m.
Besteiro (1983, 1984) from three localities of Rías
Baixas and one from Ría de Ferrol.
Remarks: Although this species is already known
from some Galician localities, it is the least frequent
species of the genus Trapania in Galicia, which makes
its mentioning in the northern end of the tombolo of A
Coruña interesting, since this is an area of open coast
and not the interior of a ‘ría’ as the previous quotes.
Trapania pallida Kress, 1968
Material: O Basteo (A Coruña), 11/07/2004, (43°
22’ 33” N; 008° 27’ 19” W). 1 specimen 14 mm long,
on red algae on rocky bottoms at a depth of 18 m.
Distribution in Galicia: Quoted by Ortea &
Urgorri (1981b) and Urgorri & Besteiro (1983, 1984)
from several localities of Rías Baixas.
Remarks: The quote on bottoms of A Coruña
extends its distribution area in Galicia to the north.
Family POLYCERIDAE Alder & Hancock, 1845
Thecacera pennigera (Montagu, 1815)
Material: Benquerencia (Lugo), 26/06/1983, (43°
33’ 47” N; 007° 10’ 42” W). 1 specimen collected
on an intertidal rocky area. Sismundi (Ortigueira),
20/08/1984, (43° 42’ 12” N; 007° 52’ 31” W). 1
specimen, collected on the infralittoral of the interior
area of Ría de Ortigueira. Viñas (Ría de Ferrol),
01/08/1996, (43° 27’ 50” N; 008° 19’ 47” W). 1
specimen 20 mm long, collected on red algae at a
depth of 14 m on rocky bottoms.
Remarks: This nudibranch, which so far had not
been mentioned in Galicia, is one of the rarest of our
coasts, as only three specimens have been collected in
three different localities and with different ecological
conditions after 36 years of research.
Crimora papillata Alder & Hancock, 1862
Material: Rabo da Porca (Ría de Ferrol),
06/03/1983, (43° 27´ 37” N; 008° 17´ 50” W). 1
specimen collected from a vertical granitic wall at a
depth of 17 m. O Segaño (Ría de Ferrol), 08/06/2005
(43° 27´ 07” N; 008° 18´ 54” W). 1 specimen 13
mm long collected at a depth of 7 m on bottoms of
small stones with great slope and strong current. O
Basteo (A Coruña), 11/07/2004, (43° 22’ 33” N; 008°
27’ 19” W). 2 specimens, the largest 13 mm long on
the briozoa Pentapora fascialis foliacea on rocky
87
Figure 4:
A: Discodoris rosi Ortea, 1979. B: Geitodoris planata (Alder & Hancock, 1846). C: Dendrodoris herytra Valdés &
Ortea, 1996. D: Tritonia plebeia Johnston, 1828. E: Doto floridicola Simroth, 1888.
F: Doto tuberculata Lemche, 1976. G: Armina maculata Rafinesque, 1814.
H: Armina tigrina Rafinesque, 1814.
88
bottoms at a depth of 18 m.
Distribution in Galicia: Polo et al. (1979) quoted
it from the northern coast in Burela (Lugo), Urgorri
& Besteiro (1983) from the southwestern coast at Ría
de Arousa (Pombeiriño) and Rolán-Álvarez & Rolán
(1989) from Illas Cíes.
Remarks: Crimora papillata is not a frequent
nudibranch on our coasts. Despite being previously
mentioned, the specimens from Ría de Ferrol extend
to the northwest coast of Galicia.
Family CHROMODORIDIDAE Bergh, 1891
Hypselodoris cantabrica Bouchet & Ortea, 1980
Material: Capela do Porto, (Meirás, Valdoviño),
30/05/1999, (43° 36’ 53” N; 008° 11’ 45” W). 12
specimens collected, but more than a hundred
observed on the bottom, the largest measuring 75
mm long. In general, they were all the same size,
collected at a depth of 10 m on rocky bottoms at a
beaten coast with Laminaria and Cystoseira. A Moa
do Segaño (Ría de Ferrol), (43° 27’ 25’’ N; 008°
18’ 42’’ W), rocky bottoms with Laminaria sp. and
Leptogorgia lusitanica at a depth of 12 m: 20/10/1985,
2 specimens, the largest 45 mm long; 27/10/1985, 3
specimens, the largest 52 mm long. O Segaño (Ría
de Ferrol), (43° 27’ 03” N; 008° 19’ 12” W), on rocky
bottoms with Laminaria sp. from 17 to 20 m deep:
17/08/1988, 7 specimens, the largest 49 mm long;
31/07/1992, 1 specimen 54 mm long; 26/08/1997, 5
specimens, the largest 46 mm long; 22/05/2002, 8
specimens, the largest 55 mm long. Fornelos (Ría de
Ferrol), (43° 28’ 02” N; 008° 18’ 49” W), on rocky
bottoms at a depth of 20 m: 24/11/2000, 1 specimen
37 mm long; 12/05/2002, 1 specimen 41 mm long.
Rabo da Porca (Ría de Ferrol), 21/07/2003, (43° 27´
37” N; 008° 17´ 50” W); 7 specimens, the largest 43
mm long, collected at a depth of 13 m on bottoms
of small stones with great slope and strong current.
A Moreira (Ría da Coruña), 10/11/2002, (43° 22’
30” N; 008° 23’ 17” W). 1 specimen 42 mm long
on rocky bottoms with small algae, with incrusting
sponges and polyclinid Ascidiacea, at a depth of 10
m. O Grelle (Ría da Coruña), 18/06/2003, (43° 22’
53” N; 008° 23’ 30” W). 2 specimens, the largest 66
mm long, on rocky bottoms with small red algae and
incrusting sponges at a depth of 12 m. As Agudelas
(A Coruña), (43° 23’ 26” N; 008° 24’ 24” W), on rocky
bottoms with small red and calcareous algae, at a
depth of 18 m: 06/04/2003, 1 specimen, 91 mm long;
21/11/2004, 2 specimens, the largest 57 mm long.
coasts, with the exception of the quote by RolánÁlvarez & Rolán (1989) at Illas Cíes.
Remarks: The species of the genus Hypselodoris
are not frequent on the coasts of Galicia, with the
exception of H. cantabrica and H. villafranca, which
are particularly abundant, despite the statement by
Bouchet & Ortea (1980), who point out in the original
description of the species that this is absent in
Galicia (‘absente sur les côtes de Galice’); the quote
of H. picta in Burela (Lugo) by Polo et al. (1979, as
Glossodoris valenciennesi) may present doubts about
their identification. In spite of the abundance of H.
cantabrica on our littoral, there is this only quote by
Rolán-Álvarez & Rolán (1989) about their presence
on our coasts, despite being frequently mentioned
in popular science articles or reports (e.g. Informe
Oceana, 2009: Cetáceos del área galaico-cantábrica.
Zonas de importancia para su conservación).
Chromodoris luteorosea (Rapp, 1827)
Material: O Zorrón (Ría de Ferrol), 19/02/2004,
(43° 27’ 22” N; 008° 20’ 23” W). 1 specimen 17 mm
long, on rocky bottoms at a depth of 36 m. As Merloeiras
(Ría de Ares), 27/07/1993, (43° 26’ 24” N; 008° 19‘ 20”
W). 1 specimen 12 mm long, collected at a depth of 30
m on rock. O Grelle (Ría da Coruña), 12/02/2004, (43°
22’ 53” N; 008° 23’ 30” W). 2 specimens, the largest
19 mm long, on the rocky channels that go down onto
sandy bottoms at a depth of 15 m.
Remarks: C. luteorosea is the most scarce species
of the genus in Galicia, being C. krohni and above all
C. purpurea more abundant.
89
Cadlina pellucida (Risso, 1826)
Material: O Segaño (Ría de Ferrol), 08/09/1985,
(43° 27’ 05’’ N; 008° 18’ 56’’ W). 1 specimen 12
mm long, collected from a vertical rocky wall with
Laminaria sp. at a depth of 17 m. Fornelos (Ría de
Ferrol), 23/05/2002, (43° 28’ 02” N; 008° 18’ 49” W).
2 specimens, being the largest 10 mm long on rocky
coasts, with the exception of the quote by RolánÁlvarez & Rolán (1989) at Illas Cíes.
Remarks: This species is by far less frequent than
Cadlina laevis, of the same genus, despite occupying
the same habitat, mainly on the infralittoral rocks
under the laminarian forest.
Family DISCODORIDIDAE Bergh, 1891
Discodoris stellifera (Vayssière, 1904)
Material: A Malata (Ría de Ferrol), 14/11/1997,
(43° 29’ 23” N; 008° 14’ 57” W). 3 specimens, the
largest 38 mm long, collected on Hymeniacidon
sanguinea under Fucus spiralis on the sides of
large stones in muddy intertidal. A Cabana (Ría de
Ferrol), (43° 29’ 12” N; 008° 15’ 29” W), among
the stones of a quay in the inferior level of the
intertidal: 24/09/1976, 1 specimen 47 mm long, on
a stone of the quay; 15/08/1980, 1 specimen 61 mm
long, on Hymeniacidon sanguinea among clusters of
Mytilus galloprovincialis. A Graña (Ría de Ferrol),
15/02/2008, (43° 28’ 53” N; 008° 15’ 26” W). 11
specimens, the largest 42 mm long, on bottoms of
sandy mud with numerous stones covered with small
algae and fauna, at a depth of 5-7 m. Promontoiro - A
Barca (Ría de Ferrol), 14/01/1979, (43° 27’ 46” N; 008°
13’ 54” W). 7 specimens, the largest 48 mm long, on
the wall of a dolphin, at a depth of 7 m, mainly
covered with Ascidiacea (Phallusia mammillata).
Distribution in Galicia: Quoted by Urgorri
& Besteiro (1983; 1984, as Discodoris planata),
quotes that correspond to those of A Cabana on the
24/09/1976 and that of Promontorio - A Barca on
90
the 14/01/1979, listed in the Material of the previous
paragraph.
Remarks: In the specimens of 15/08/1980 and
24/09/1976, it was found that all spicules present in their
faecal pellets belonged to the sponge Hymeniacidon
sanguinea; the 3 specimens of 14/11/1997 were
located on the same sponge. Besides, by what has
been observed in the localities of Ría de Ferrol, this
species had always been collected on stones and
quays in protected environments, with certain pellitic
sedimentation, in areas covered with fucaceous algae
or masses of Mytilus galloprovincialis.
Discodoris rosi Ortea, 1979
Material: Fornelos (Ría de Ferrol), (43° 27’
59” N; 008° 18’ 48” W): 06/07/1986, 2 specimens,
the largest 52 mm long, on rocky bottoms with red
sponges at a depth of 20 m; 23/08/1997, 1 specimen
25 mm long on rocky bottoms at a depth of 17 m;
23/05/2002, 2 specimens, the largest 29 mm long on
rocky bottoms at a depth of 19 m. O Vispón (Ría de
Ferrol), (43° 27’ 56” N; 008° 16’ 05” W), on thick
shelly gravel bottoms, at a depth of 20 and 21 m:
16/11/2005, 2 specimens, the largest 29 mm long;
03/12/2009, 1 specimen 10 mm long. A Bestarruza
(Ría de Ferrol), 11/05/2008, (43° 27’ 49” N; 008°
15’ 42” W). 2 specimens, the largest 26 mm long,
collected at a depth of 18 m on bottoms of stones
covered with very diverse fauna. Punta Herminia
(A Coruña), 27/03/2003, (43° 23’ 25” N; 008° 24’
02” W). 7 specimens together on red sponges, the
largest 34 mm long, on a rock at a depth of 15 m. As
Agudelas (A Coruña), 06/04/2003, (43° 23’ 26” N;
008° 24’ 24” W). 21 specimens, but only 6 collected,
the largest 38 mm long, on rocky bottoms with small
red and calcareous algae, at a depth of 18 m. Orzán
(A Coruña), 25/04/1982, (43° 22’ 42” N; 008° 24’ 36”
W). 3 specimens collected on the sponge Microciona
ascendens on an intertidal rocky area.
Distribution in Galicia: This species was quoted
for the first time at Illa de Ons (Ortea & Urgorri,
1979a), this mention was subsequently extended to
Illas Cíes (Urgorri & Besteiro, 1983, pers. comm. B.
Picton; Rolán-Álvarez & Rolán, 1989). Rolán (1983)
records this mentioning by Picton.
Remarks: D. rosi is a very frequent species at
the ‘rías’ of Golfo Ártabro, mainly on the lowest
infralittoral rocky areas, from the end of the
laminarian forest downwards; many more specimens
have been observed than those listed herein, they are
very frequently observed making up groups of 5 to 8
individuals.
Geitodoris planata (Alder & Hancock, 1846)
Material: A Graña (Ría de Ferrol), 19/11/2010, (43°
28’ 43” N; 008° 15’ 35” W). 3 specimens, the largest 26
mm long, in the sea water tank of the Station of Marine
Biology of A Graña. A Redonda (Ría de Ferrol), (43°
27’ 46” N; 008° 16’ 10” W), first infralittoral levels
(0-1 m deep) under stones covered with sponges:
02/11/1978, 1 specimen 27 mm; 31/12/1978, 1 specimen
25 mm long. O Baño (Ría de Ferrol), 22/08/1986, (43°
27’ 39” N; 008° 15’ 59” W). 1 specimen 28 mm long,
collected on a stone covered with algae, at a depth of 9
m. Ría de Ferrol, 14/11/1997, (43° 28’ 15” N; 008° 15’
09” W). 1 specimen 12 mm long, dredged on shelly
gravel bottoms at a depth of 8 m in the central area of
the ‘ría’.
Besteiro (1983; 1984), quotes that correspond to those
of A Redonda on the 02/11/1978 and 31/12/1978, listed
in the Material of the previous paragraph.
Remarks: The specimens mentioned above match
up with the descriptions made by Cervera et al.
(1985), Ortea (1990) and Valdés (2002), with the end
of the gills and rhinophores in white, their backs
covered with small tubercles and a dorso-lateral
arrangement of the darker spots; however, some
specimens are darker than others depending on the
size of their dark brown spots, which are larger in
the specimens with large size. Geitodoris planata
was always collected in less protected environments
with higher hydrodynamics than those inhabited by
Discodoris stellifera (vide supra); they are bottoms of
small stones covered with small algae, whose inferior
surface is colonized by incrusting animals, mainly
Porifera, Briozoa and Ascidiacea.
Family DENDRODORIDIDAE O’Donoghue, 1924
Dendrodoris herytra Valdés & Ortea, 1996
Material: Leuseda (Ría de Ferrol), 07/04/1983,
(43° 27’ 57” N; 008° 16’ 30” W). 1 specimen 12 mm
long, on a valve on shelly gravel bottoms at a depth
of 15 m.
Distribution in Galicia: The only mention of this
species on our coasts corresponds to the quote of Illas
Cíes (Rolán-Álvarez & Rolán, 1989; Rolán, Otero &
Rolán-Álvarez (1989, as D. grandiflora).
Remarks: This is a little frequent species on the
northern Iberian littoral; the present mention extends
the distribution area of Galicia to the north.
Suborder CLADOBRANCHIA Willan & Morton, 1984
Infraorder DENDRONOTINA Sars, 1878
Family TRITONIIDAE Lamarck, 1809
Tritonia plebeia Johnston, 1828
Material: A Redonda (Ría de Ferrol), 20/08/1986,
(43° 27’ 52” N; 008° 16’ 15” W). 8 specimens, the
largest 12 mm long, collected at a depth of 20 m on the
basal part of a colony of Alcyonium digitatum located
on a rocky wall.
Distribution in Galicia: It has been quoted
from several localities of Rías Baixas by Urgorri &
Besteiro (1983) and in an imprecise way by Rolán
(1983) in Vigo.
Remarks: The present mention corresponds to the
northermost Iberian quote, extending its distribution
area in Galicia to the north and being also one of the
few quotes from the Iberian Peninsula.
Family DOTOIDAE Gray, 1853
Doto floridicola Simroth, 1888
Material: Viñas (Ría de Ferrol), 01/01/1996, (43°
27´ 50” N; 008° 19´ 47” W). 2 specimens 6 mm long,
91
Figure 5:
A: Flabellina affinis (Gmelin, 1791). B: Favorinus blianus Lemche & Thompson, 1974. C: Babakina anadoni (Ortea,
1979). D: Cerberilla bernadettae Tardy, 1965. E: Eubranchus linensis García-Gómez, Cervera & García, 1990.
F: Pseudovermis papillifer Kowalevsky, 1901. G: Calma gobioophaga Calado & Urgorri, 2002.
H: Cuthona nana (Alder & Hancock, 1842).
92
collected at a depth of 14 m on rocky bottoms on
the hydrozoa Aglaophenia kirchenpaueri. Fornelos
(Ría de Ferrol), (43° 28’ 02” N; 008° 18’ 49” W):
05/08/1996, 6 specimens, the largest 5.5 mm long,
collected at a depth of 20.5 m on rocky bottoms on
A. kirchenpaueri; 28/08/1996, 2 specimens 6.5 and
7 mm long, collected on A. kirchenpaueri on rocky
Remarks: This species is quite rare in Galicia,
being the northernmost Iberian quote; it is much more
abundant on the coast of Arrabida (Portugal), from
where we have several specimens.
Doto tuberculata Lemche, 1976
Material: A Redonda (Ría de Ferrol), 03/03/1992,
(43° 27’ 52” N; 008° 16’ 15” W). 1 specimen 13
mm long at a depth of 9 m on rocky bottoms on
Sertularella gayi. Fornelos (Ría de Ferrol), (43° 28’
02” N; 008° 18’ 49” W), on rocky bottoms on the
hydrozoa Sertularella gayi from 16 to 20 m deep:
20/07/2005, 6 specimens from 4 to 6.5 mm long;
22/07/2005, 12 specimens from 4.5 to 6.2 mm long;
19/08/2005, 2 specimens 8.5 mm long; 04/01/2006, 1
specimen 7 mm long; 10/01/2006, 1 specimen 6.5 mm
long. Barbeira (Ría de Ferrol), 11/04/2006, (43° 28’
08” N; 008° 19’ 07” W). 4 specimens, the largest 6.5
mm long, collected on Sertularella gayi at a depth of
15 m on muddy bottoms with some loose stones with
several species of hydrozoa. Castelo de San Felipe (Ría
de Ferrol), 29/08/2006, (43° 27’ 46” N; 008° 16’ 50”
W). 4 specimens, the largest 6 mm long, collected on
Sertularella gayi on rocky bottoms at a depth of 14 m.
Distribution in Galicia: The only quote of this
species known so far in Galicia (Ortea & Urgorri,
1978) is that of a specimen from Reinante (Lugo).
Remarks: All quotes of D. tuberculata in Galicia
by Ortea & Urgorri (1978), Fernández-Ovies (1981),
Fernández-Ovies & Ortea (1981) and Urgorri &
Besteiro (1983, 1984), correspond to the same animal
from Reinante; this species is not rare in Galicia,
but lives in a very specific habitat. The numerous
specimens collected so far were on the hydrozoa
Sertularella gayi located on the lower parts of
rocks and stones in areas with a certain pellitic
sedimentation.
Infraorder ARMININA Odhner, 1934
Family ARMINIDAE Iredale & O’Donoghue, 1923
Armina maculata Rafinesque, 1814
Material: Canal do Grove (Ría de Arousa),
14/11/1990, (42° 27’ 50’’ N; 008° 58’ 14’’ W). 11
specimens, the largest 171 mm long, collected at
a depth of 60 m on maërl bottoms with Veretillum
cynomorium and Pteroides griseum.
Remarks: The presence of this species is bound
to that of the Pennatulacea Veretillum cynomorium on
which it feeds.
Armina tigrina Rafinesque, 1814
Material: Canal do Grove (Ría de Arousa),
14/11/1990, (42° 27’ 50’’ N; 008° 58’ 14’’ W). 7
specimens from 34 to 54 mm long, collected at a
depth of 60 m on a bottom of maërl with Veretillium
cynomorium and Pteroides griseum.
Remarks: As A. maculata, the presence of this
species is bound to that of Pennatulacea; however, it
could not be proved if it fed on the aforementioned
Alcyonaria, but presumably it does.
Infraorder AEOLIDINA Odhner, 1934
Family FLABELLINIDAE Bergh, 1889
Flabellina affinis (Gmelin, 1791)
Material: Fornelos (Ría de Ferrol), 22/11/1998,
(43° 28’ 02” N; 008° 18’ 49” W). 3 specimens, the
largest 18 mm long, collected at a depth of 17 m on
rocky bottoms.
93
Remarks: This nudibranch is rare in Galicia and
unknown in the NW and N of the Iberian Peninsula
(Cervera et al., (2004), being these specimens the
northernmost Iberian quote.
Family FACELINIDAE Bergh, 1889
Favorinus blianus Lemche & Thompson, 1974
Material: Fornelos (Ría de Ferrol), 09/08/1992,
(43° 28’ 02” N; 008° 18’ 49” W). 11 specimens, the
largest 16 mm long, collected at a depth of 20 m on
rocky bottoms on red algae, where numerous clutches
of Aeolidacea were present.
Distribution in Galicia: It was mentioned for the
first time by Ortea & Urgorri (1981b) from Pedras
Negras (Pontevedra); Urgorri & Besteiro (1983)
record this same specimen in their inventory, another
one from Illa de Ons and a third one from Pombeiriño
(Ría de Arousa).
Remarks: The specimens from Fornelos extend
their distribution in Galicia to the north as far
as Golfo Ártabro. This quote corresponds to the
northernmost mention of the species in the Iberian
Peninsula. Outside our coasts, it is only known from
the coast of Arrabida (Gavaia et al., 2003).
Pruvotfolia pselliotes (Labbé, 1923)
Material: Ría de Ferrol, 23/06/1993, (43° 28’ 20’’
N; 008° 15’ 02’’ W). 1 specimen 20 mm long on the
concavity of a valve from shelly gravel bottoms at a
depth of 12 m.
Distribution in Galicia: Ortea & Urgorri (1981a)
quoted it for the first time in Galicia from Pedras
Negras (Pontevedra) and Rolán-Álvarez & Rolán
(1989 as P. pselloides) mentioned it from Illas Cíes.
This specimen from Ferrol corresponds to the third
mention, extending its distribution in Galicia as far
as Golfo Ártabro.
Remarks: This species was mentioned in Galicia
by Ortea & Urgorri (1981a) and Urgorri & Besteiro
(1983) but both quotes correspond to the same
94
specimen from Pedras Negras; the quote by Ortea
(1977a) corresponds to western Asturias.
Babakina anadoni (Ortea, 1979)
Material: A Bestarruza (Ría de Ferrol),
18/11/2007, (43° 27’ 49” N; 008° 15’ 42” W). 1
specimen 26 mm long, collected at a depth of 16 m on
bottoms of stones covered with very diverse fauna. O
Cabalo (Ría da Coruña), 29/09/2002, (43° 23’ 05” N;
008° 23’ 26” W). 1 specimen 38 mm long, on a rock
with small red algae and Corynactis viridis under the
laminarian forest at a depth of 10 m. San Vicente do
Mar (O Grove), 03/12/1982, (42° 27’ 10” N; 008° 55’
25” W). 1 specimen 21.5 mm long, under a stone in a
granitic tray covered on the surface with Ulva sp., in
the first infralittoral levels.
Distribution in Galicia: The only mention of
this species on our coasts corresponds to 3 specimens
from the entrance of Ría de Vigo: Illas Cíes and Cabo
de Home (Rolán, Rolán-Álvarez & Ortea, 1991).
Remarks: This species of unquestionable Atlantic
distribution in the Iberian Peninsula, is quite rare in
Galicia. Every time it was observed, its individuals
were isolated and could not be related to a specific
habitat or prey species.
Family AEOLIDIIDAE D’Orbigny, 1834
Aeolidiella glauca (Alder and Hancock, 1845)
Material: San Cristovo (Ría de Ferrol), 15.09.1977
(43° 27’ 56’’ N; 008° 18’ 06’’ W). 1 specimen of 15
mm at a depth of 4.5 m under a stone in the area of the
laminarian forest.
Remarks: Of the species of the genus Aeolidiella
present on our coasts, A. glauca is by far less frequent
than A. sanguinea and A. alderi.
Cerberilla bernadettae Tardy, 1965
Material: Ría de Ferrol, 08/08/1987, (43° 28’
10’’ N; 008° 14’ 47’’ W). 2 specimens 5 mm long
on muddy shelly gravel at a depth of 15 m. Ría de
Ferrol, 25/08/1987 (43° 28’ 10’’ N; 008° 12’ 43’’ W). 1
specimen 11 mm long on mud at a depth of 8 m. Ría
de Ares, from 01/11/1987 to 31/07/1996 (43° 22’ 57’’
N - 43° 25’ 18’’ N; 008° 13’ 29’’ W - 008° 17’ 32’’ W),
at a depth from 10 to 26 m on bottoms of muddy sand,
mud and silty sand. 29 specimens, the largest 8.5 mm
long, all fixed together with the sediment.
Remarks: This species presents, on our coasts,
a shallow digging habit on the infralittoral bottoms
of muddy sand and sandy mud, with moderate values
of organic matter, in which the anemone Edwardsia
sp. is often present. Dr. Cervera was informed of the
presence of this species at the ‘rías’ of Golfo Ártabro,
who included the quote in Cervera et al., (2004) as a
pers. comm.
Family EUBRANCHIDAE Odhner, 1934
Eubranchus linensis García-Gómez, Cervera &
García, 1990
Material: O Pereiro (Ría de Ferrol), 20/02/1987,
(43° 28’ 01” N; 008° 16’ 15” W). 2 specimens 10
mm long on the Hydrozoa Halecium sp. on rocky
bottoms at a depth of 9 m. San Felipe (Ría de Ferrol),
22/08/2007, (43° 27’ 47” N; 008° 18’ 57” W). 1
specimen 10 mm long, on rocky bottoms at a depth of
18 m. Punta Herminia (A Coruña), 27/03/2003, (43°
23’ 25” N; 008° 24’ 02” W). 2 specimens together on
the hydraria Halecium sp., the largest 11 mm long, on
a rock at a depth of 15 m.
coasts, it is the first quote for Galicia.
Remarks: These specimens match up with the
chromatic model of the original description (GarcíaGómez, Cervera & García, 1990), identification that
was subsequently corroborated by Dr. Cervera, who
included the quote in Cervera et al., (2004) as a
pers. comm. It also corresponds to the northernmost
mention of the species.
Family PSEUDOVERMIDAE Thiele, 1931
Pseudovermis papillifer Kowalevsky, 1901
Material: O Baño (Ría de Ferrol), 18/11/2007,
(43° 27’ 47” N; 008° 15’ 57” W). 1 specimen 3.5 mm
long on a slightly muddy shelly gravel bottom at a
depth of 18 m.
Remarks: Urgorri (1981) mistakenly mentions
P. papillifer for Galicia, which was subsequently
described (Urgorri, Cobo & Besteiro, 1991) as the
new species Pseudovermis artabrensis, Urgorri, Cobo
& Besteiro, 1991.
Family CALMIDAE Iredale & O’Donoghue, 1923
Calma glaucoides (Alder & Hancock, 1854)
Material: Burela (Lugo), 18/05/1999, (43° 38’ 50”
N; 007° 20’ 35” W). 8 specimens, one on a spawn of
Lepadogaster lepadogaster and 7 on another spawn
of Lepadogaster candollei. Ría de Ferrol, 03/06/2004,
(43° 28’ 15” N; 008° 15’ 09” W). 2 specimens 6 mm
long, dredged on gravel bottoms at a depth of 8 m in
the central area of the ‘ría’.
Distribution in Galicia: Only quoted by Calado
& Urgorri (2002).
Remarks: Calma glaucoides was mistakenly
quoted by Urgorri & Besteiro (1983, 1984); Calado
& Urgorri (2002) subsequently proved that such
specimens belonged to a new species: Calma
gobioophaga, being these the only quotes (Burela
and Ría de Ferrol) known at present.
Calma gobioophaga Calado & Urgorri, 2002
Material: A Cabana (Ría de Ferrol), 05/08/1978,
(43° 29’ 10” N; 008° 15’ 29” W). 1 specimen (Paratype
2) 4 mm long at a depth of 2 m on unidentified fish
spawn; deposited at the Museo de Historia Natural
‘Luis Iglesias’ (MCNS), Santiago de Compostela,
Spain, with the registration number MCNS-5MO.
95
Cambados (Ría de Arousa), 27/07/1979, (43° 31’ 17”
N; 008° 49’ 18” W). 58 specimens (type series of
Galicia), the largest 10 mm long, collected at a depth
of 3 m under the stones of a breakwater covered with
spawns of Gobius niger. Leuseda (Ría de Ferrol),
19/08/1979, (43° 28’ 03” N; 008° 16’ 38” W). 2
specimens (type series of Galicia), the largest 6.5 mm
long, at a depth of 8 m, on bottoms of muddy sand, on
a tube of the Polychaeta Chaetopterus variopedatus
covered with the hydrozoa Antennella secundaria
with numerous spawns of Doto sp.
Besteiro (1983, 1984, both as C. glaucoides) and
Calado & Urgorri (2002).
Remarks: As it was previously commented, the
specimens listed in the Material were mistakenly listed
as C. glaucoides by Urgorri & Besteiro (1983, 1984);
therefore, they all constitute the part of the type series
collected in Galicia and the specimen of 05/08/1978
is Paratype 2; the type series Material from Galicia
is deposited in the collection of Victoriano Urgorri at
the Universidade de Santiago de Compostela (Spain).
Family TERGIPEDIDAE Thiele, 1931
Cuthona nana (Alder & Hancock, 1842)
Material: San Amede (Ría de Ares), 27/08/1985,
(43° 23’ 23” N; 008° 16’ 15” W). 2 specimens on
Hydractinia echinata located on shells occupied
by Pagurus bernhardus on muddy sand bottoms at
a depth of 16 m. A Graña (Ría de Ferrol), (43° 28’
44” N; 008° 15’ 33” W), 8 specimens collected on
Hydractinia echinata located on shells occupied by
Pagurus bernhardus on mud bottoms at a depth of
11-12 m: 13/09/1985, 16/02/1987, 26/03/1994. Rabo da
Porca (Ría de Ferrol), 11/05/1987 (43° 27’ 27’’ N; 008°
18’ 15’’ W). 3 specimens on Hydractinia echinata
with Pagurus bernhardus on gravel bottoms, mud
and shells at a depth of 16 m.
Remarks: Cuthona nana is not a rare species
on our littoral despite not being mentioned so far in
96
Galicia or any other locality of the Iberian Peninsula
(Cervera et al., 2004), the absence of previous
mentions may be due to the specific habitat it lives
in: on Hydractinia echinata which covers the shells
occupied by the small and medium sized hermit crab
Pagurus bernhardus. It is not easy to detect in situ
the presence of C. nana on the hydraria, as its cerata
may be mistaken for the tentacles of the polyps. By
studying the shells covered with H. echinata under
stereoscopic microscope, not only can the nudibranch
be distinguished, but also its spawn in the shape of a
cord with its eggs grouped together like rosary beads.
DISCUSSION
The systematic studies have been given
a boost in the last decades, not only due to the
use of new techniques and instruments, but also
due to a more modern conception than the mere
descriptions of external anatomy of the animals.
New species are described based on observations
in vivo, with morphological criteria, external and
internal, reproductive and trophic and sometimes
primarily distinguished by ecological criteria (Calado
& Urgorri, 2002). The revisions and monographs of
genera and other superior taxonomic categories are
made with wide collections of animals from different
geographical areas and to a great extent they are
already based on morphological or morphologicalmolecular phylogenetic analyses (Valdés, 2002).
Undoubtedly, systematics is a formative Science of
continuous learning, so wide that it may go further
than the length of the scientific life of any researcher;
it is complex, difficult and to a certain extent elitist, as
those who do not have this capacity, are limited in the
right understanding of biodiversity. Due to its inherent
difficulty, it is sometimes disdained for those who do
not know it, but the ecological, and evolutionary value
and even the value as heritage that the knowledge of
biodiversity has recently won, has given Science its
worth in a way it had never had before.
Therefore, the renewed importance of inventories
of species living in different environments and specific
geographical areas, is unquestionable to document
biodiversity. This allows us to have a more accurate
view of the functioning of benthonic communities,
to know how far a single species can colonize an
area and how big and uneven the areas of high or
low biodiversity are. Galicia is a geographical area,
which needs some faunistic studies and analyses that
can give a real view of the dimension of biodiversity,
which is why contributions as these presented in this
article are so important.
As a whole, the 36 species of Opisthobranchia
quoted correspond to: 1 Cephalaspidea, 1 Anaspidea,
2 Acochlidiomorpha, 2 Sacoglossa, 14 Nudibranchia
Anthobranchia, 16 Nudibranchia Cladobranchia, of
which 3 are Dendronotina, 2 Arminina and 11 Aeolidina.
Of these, 13 species are quoted for the first time in
Galicia, of which there was no record on our coasts:
Gastropteron rubrum, Okenia aspersa, Thecacera
pennigera, Chromodoris luteorosea, Doto floridicola,
Armina maculata, Armina tigrina, Flabellina affinis,
Aeolidiella glauca, Cerberilla bernadettae, Eubranchus
linensis, Pseudovermis papillifer and Cuthona nana.
In general, they are all rare or little frequent species
on our coasts, with the exception of Cuthona nana
and Cerberilla bernadettae, which are present in very
specific habitats that make them go unnoticed.
Of the 23 remaining species that are mentioned
in this article, Aplysia fasciata, Hermaea bifida,
Hypselodoris cantabrica, Cadlina pellucida,
Dendrodoris herytra, Doto tuberculata and Babakina
anadoni are quoted for the second time on our coasts.
Babakina anadoni is the rarest presence, as such a
striking animal does not easily go unnoticed and the
scarce specimens observed, were isolated individuals
that could not be assigned to a specific habitat.
In contrast, Hypselodoris cantabrica and Doto
tuberculata are very frequent, at least at the ‘rías’ of
Golfo Ártabro; H. cantabrica is plentiful on rocky
bottoms, beaten infralittorals under the laminarian
forest and D. tuberculata in deeper rocky areas of less
beaten environments, always in the lowest areas of
the rocks under the hydrozoa Sertularella gayi whose
colonies are covered with a thin film of very thin mud
which makes the animal practically indiscernible.
Not many other records of Asperpina loricata and
Microhedyle glandulifera apart from those presented
by Cobo (1985) are provided herein, but the inclusion
of these species is due to a double reason that had to
be clarified. Arnaud et al. (1986) did not collect or
study any specimens from Galicia as their mention
was taken from the dissertation of Cobo (1984);
besides, the quotes by Cobo (1985) went unnoticed as
they were published in a small popular science book.
With this aim, the mention of Calma glaucoides
and C. gobioophaga, species recently published by
Calado & Urgorri (2002), is included herein. In this
article, C. gobioophaga is described as a new species,
based on specimens from Portugal and Galicia, but
the Galician specimens prior to 1983 were quoted
by Urgorri & Besteiro (1983, 1984) as C. glaucoides,
which is why it was important to clarify which of
these belonged to the first or second species.
Discodoris stellifera and Geitodoris planata were
included with an identical clarifying intention. The
specimens captured prior to 1983 were all quoted by
Urgorri & Besteiro (1983, 1984) as Discodoris planata,
which is why it was important to clarify which of those
quotes corresponded to G. planata and which to D.
stellifera. Besides, new records of both species are
incorporated and information on the specific habitat
that both occupy at the Ría de Ferrol is provided, as
well as the diet of D. stellifera, which feeds on the
Porifera Hymeniacidon sanguinea proved by analysis
of the spicules contained in its faecal pellets.
Of the rest of species: Hermaeopsis variopicta,
Corambe testudinaria, Trapania tartanella, Trapania
maculata, Trapania pallida, Crimora papillata,
Discodoris rosi, Tritonia plebeia, Favorinus blianus
and Pruvotfolia pselliotes, new localities are provided
which extend their distribution on the Galician coasts,
despite being previously quoted in Galicia and little
frequent or rare species.
97
ACKNOWLEDGEMENTS
The authors wish to thank all present and past
members of the Research Team 1275 of the USC for
their help in the collection of samples, especially
Dr. Juan Moreira, Marcos P. Señarís and Marcos
Abad. Many thanks to Julia García Carracedo for
the English version of the manuscript. This article
is a contribution to the projects: XUGA20005B95,
XUGA20006B98, PGIDT01PXI20008PR, CTM200400740, A Selva-08, PGIDIT05PXIC20001P and
PGIDIT07PXB000120PR.
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BYE BYE “OPISTHOBRANCHIA”!
A REVIEW ON THE CONTRIBUTION OF MESOPSAMMIC SEA
SLUGS TO EUTHYNEURAN SYSTEMATICS
SCHRÖDL M(1), JÖRGER KM(1), KLUSSMANN-KOLB A(2) & WILSON NG(3)
Key words: Mollusca, Heterobranchia, morphology, molecular phylogeny, classification, evolution.
ABSTRACT
During the last decades, textbook concepts
of “Opisthobranchia” have been challenged by
morphology-based and, more recently, molecular
studies. It is no longer clear if any precise distinctions
can be made between major opisthobranch and
pulmonate clades. Worm-shaped, mesopsammic taxa
such as Acochlidia, Platyhedylidae, Philinoglossidae
and Rhodopemorpha were especially problematic in
any morphology-based system. Previous molecular
phylogenetic studies contained a very limited sampling
of minute and elusive meiofaunal slugs. Our recent
multi-locus approaches of mitochondrial COI and 16S
rRNA genes and nuclear 18S and 28S rRNA genes
(“standard markers”) thus included representatives
(1) Bavarian State Collection of Zoology. Münchhausenstr. 21,
D-81247 Munich, Germany.
(2) Institute for Ecology, Evolution and Diversity, GoetheUniversity, Siesmayerstr. 70, 60054 Frankfurt am Main,
Germany.
(3) The Australian Museum, 6 College Street, Sydney NSW,
2010 Australia.
Email: [email protected], Katharina.Joerger@
zsm.mwn.de, [email protected], Nerida.
[email protected]
of most mesopsammic “opisthobranchs” within a
comprehensive euthyneuran taxon set.
The present study combines our published
and unpublished topologies, and indicates that
monophyletic Rhodopemorpha cluster outside of
Euthyneura among shelled basal heterobranchs, acteonids are the sister to rissoellids, and Nudipleura
are the basal offshoot of Euthyneura. Furthermore,
Pyramidellidae, Sacoglossa and Acochlidia cluster
within paraphyletic Pulmonata, as sister to remaining
“opisthobranchs”. Worm-like mesopsammic heterobranch taxa have clear independent origins and thus
their similarities are the result of convergent evolution. Classificatory and evolutionary implications
from our tree hypothesis are quite dramatic, as shown
by some examples, and need to be explored in more
detail in future studies.
We do not claim that these concatenated “standard
marker” gene trees reflect the true phylogeny of
all groups; exploring additional, suitable markers
is required. We do claim, however, that improved
taxon sampling and improved data quality (such
as sequences, alignments) were beneficial towards
101
SCHRÖDL M, JÖRGER KM, KLUSSMANN-KOLB A & WILSON NG
revealing relationships of higher euthyneuran taxa,
and that phylogenetic hypotheses based on this data
set are converging. The traditional taxon concept of
Opisthobranchia is clearly artificial and thus obsolete.
Novel phylogenetic hypotheses, as disturbing they
may be at first glance, give us the opportunity and
perhaps the obligation to refine our approaches and
rethink older paradigms. Most importantly, we see
no more way to explore morphology, systematics and
evolution of “opisthobranchs” separately from “lower
heterobranchs” and “pulmonates”.
INTRODUCTION
Milne Edwards (1848) split the gastropods into
Prosobranchia, Pulmonata and Opisthobranchia. The
latter two taxa are usually combined as Euthyneura.
Both researchers and amateurs easily associate
opisthobranchs as marine slugs or snails, with a more
or less reduced or internalized shell, having an almost
bilaterally symmetrical body and either a head shield
or head tentacles, whereas pulmonates appear almost
exclusively related to limnic and terrestrial habitats.
Unconventional taxa such as interstitial worm-like
forms, limnic opisthobranchs and marine pulmonates
occur, but are obviously too exceptional to challenge
the practical value of the traditional OpisthobranchiaPulmonata concept. The often beautifully coloured
and bizarrely shaped approx. 6000 opisthobranch
species thus are treated as belonging to a clade
in virtually all older field guides and zoological
textbooks (e.g. Westheide & Rieger, 2007), current
molluscan classifications (e.g. Bouchet & Rocroi,
2005), and reviews (e.g. Schmekel & Portmann, 1982,
Schmekel, 1985, Rudman & Willan, 1998), including
the most recent one by Wägele et al. (2008) that
was published within a compendium on molluscan
phylogeny and evolution (Ponder & Lindberg, 2008).
Recent comprehensive field guides on Caribbean and
Indo-Pacific opisthobranchs, however, left monophyly
open (Valdés et al., 2006, Gosliner et al., 2008).
There has always been a certain disagreement with
regards to which major subtaxa should be included
102
into Opisthobranchia (Gosliner, 1981). Commonly
accepted “core groups” are Cephalaspidea, Anaspidea,
Thecosomata, Gymnosomata, Sacoglossa, Acochlidia,
Tylodinoidea (=Umbraculida) and Nudipleura, the
latter consisting of side-gilled Pleurobranchomorpha
and Nudibranchia, which are the sea slugs in a strict
sense. Some taxa with more or less well-developed
helicoidal shells such as Acteonoidea (see Mikkelsen,
1996 vs. 2002) and Pyramidelloidea (e.g. Fretter &
Graham, 1949) and the limpet-like Siphonarioidea
have also occasionally been discussed as part of
Opisthobranchia (see review by Wägele et al., 2008).
While the worm-like Rhodopemorpha were either
seen as turbellarians or transitional forms between
worms and gastropods in early approaches, most
modern authors treated them as euthyneurans or
integral part of opisthobranchs (e.g. Haszprunar &
Heß, 2005).
Establishing the Heterobranchia concept,
Haszprunar (1985, 1988) reconstructed an apomorphybased phylogeny implying a progressive evolution
from simple “allogastropod” (=“lower heterobranch”)
taxa such as Valvatoidea, Architectonicoidea
and Pyramidelloidea towards Pentaganglionata
(=Euthyneura). Haszprunar’s phylogeny showed
Acteonoidea (Architectibranchia) as the sister to
monophyletic Pulmonata (including pentaganglionate
Rhodopemorpha), which was itself the sister to
remaining opisthobranchs (including vermiform
Smeagolidae),
rendering
“Opisthobranchia”
paraphyletic. Haszprunar thus was the first to
phylogenetically infer and discuss the artificial
nature of Opisthobranchia rather than comparing
similarities and modifying the inclusiveness of the
concept. Using cladistic analyses on a morphological
dataset, Salvini-Plawén & Steiner (1996) recovered
monophyletic Euthyneura, and Pulmonata plus
Thecosomata as sister to remaining Opisthobranchia
including Rhodopemorpha (as Rhodopida) as sister
to equally shell-less and small-sized Acochlidia
and Gymnosomata. Dayrat & Tillier (2002) found
Pyramidelloidea within euthyneuran taxa and
summarized an unresolved euthyneuran topology with
A REVIEW ON THE CONTRIBUTION OF MESOPSAMMIC SEA SLUGS TO EUTHYNEURAN SYSTEMATICS
„Lower heterobranchs“
i l di Rhodopemorpha
including
Rh d
h
Rissoelloidea
Acteonoidea
Nudipleura
Heterobranchia
Euthyneura
y
s.l.
Euopisthobranchia
Tectipleura
p
new name
Panpulmonata
Umbraculoidea
Runcinacea
Cephalaspidea s.s.
Anaspidea
p
Pteropoda
Siphonarioidea
Sacoglossa
Glacidorboidea
Amphiboloidea
Pyramidellidae
Hygrophila
Acochlidia
Eupulmonata
Figure 1:
“Opisthobranch” phylogeny as inferred from “standard genes” analyses, combining results by Jörger et al. (2010) and Wilson et al. (2010); robustly
supported nodes (bootstrap support >75 and posterior probability >0.95) indicated by black dots. Taxa formerly regarded as opisthobranchs in
green, pulmonate taxa in yellow, “lower heterobranch” taxa in blue. Note that the assemblage of “Lower heterobranchs including Rhodopemorpha”
is paraphyletic but collapsed for illustrative purposes.
monophyletic Pulmonata arising as one of many clades
from an opisthobranch grade of organization. An even
more comprehensive morphology-based parsimony
analysis by Wägele & Klussmann-Kolb (2005) showed
Pteropoda (Gymnosomata plus Thecosomata) as sister
to Pulmonata plus remaining Opisthobranchia, but
this is contradicted by a more focused molecular study
(Klussmann-Kolb & Dinapoli, 2006). In the study by
Wägele & Klussmann-Kolb (2005) the remaining
Opisthobranchia included a clade of exclusively
interstitial (and/or small sized) cephalaspidean
subtaxa, Rhodopemorpha and Acochlidia as sister
to Sacoclossa, rendering Cephalaspidea polyphyletic.
In the light of the latest morphology-based cladistic
analysis focussing on Acochlidia (Schrödl & Neusser,
2010), such results are in doubt. While resolving
inner relationships of Acochlidia quite nicely, other
mesopsammic euthyneurans included, regardless
their supposed affiliation, had a tendency to cluster
with Acochlidia; Schrödl & Neusser (2010) explained
that by parallel concerted reductions of body-size and
organs, but also by convergent evolution of vermiform
bodies having a set of special organs as adaptations to
a special habitat. Summarizing, 1) the Heterobranchia
concept has always conflicted with a monophyletic
Opisthobranchia, 2) no morphology-based analyses
have recovered a monophyletic Opisthobranchia, 3)
morphology-based analyses are mislead by problems
of interpreting morphological similarities and
a generally high degree of parallelism (Gosliner,
1981, 1991); in particular, convergences displayed
by small-sized slugs that occur in many subgroups
may outnumber characters showing true phylogenetic
signal, and thus lead to unreliable or completely
wrong topologies.
Molecular markers, in contrast, offer an extremely
large number of characters (via nucleotide sequences)
103
and many genes such as rRNA genes may not be
directly influenced by habitat-specific ecological
selective pressures. Early molecular approaches on
opisthobranch phylogeny counted with single genes
(partial 16S rDNA, Tholleson, 1999a,b, Wägele et
al., 2003; 18S rDNA, Wollscheid & Wägele 1999;
partial 28S rDNA, Dayrat et al., 2001), for relatively
small sets of taxa. Whenever pulmonates were
included in such analyses, opisthobranchs were
not recovered as monophyletic unless the taxon
definitions were extraordinarily modified. The same
happened to the mitochondrial genome-based data
sets of Grande et al. (2004a,b, 2008) and Medina
et al. (2011). Vonnemann et al. (2005) were the
first to combine the more conservatively evolving
nuclear 18S and 28S rRNA gene fragments sequenced
from a larger and more representative euthyneuran
taxon set (including 3 different acochlidian species),
recovering monophyletic Opisthobranchia as sister
to potentially paraphyletic Pulmonata, but only in
Maximum Parsimony analysis of the combined data
set. Successively extending the taxon sampling to
further pulmonate subgroups and especially to lower
heterobranchs, using a combined set of mitochondrial
CO1, 16S rRNA gene fragments, and nuclear 18S
rRNA (complete) plus 28S rRNA genes (D1-3), and
applying Maximum Likelihood algorithms became
the standard for further analyses. None of the
studies increasing in sophistication (e.g. KlussmannKolb et al., 2008, Dinapoli & Klussmann-Kolb,
2010) recovered a monophyletic Opisthobranchia,
usually due to acochlidian, but also sacoglossan and
pyramidelloidean taxa clustering among pulmonates.
Since we failed to trace the origin of Acochlidia
in morphology-based frameworks (Schrödl &
Neusser, 2010), we carefully designed molecular
studies including representatives of all the hardto-find groups with interstitial slugs and all but
one acochlidian families, plus all taxa that were
mentioned to be potentially related to some of them
(Jörger et al., 2010, Wilson et al., 2010). Special
attention was paid to alignments and to the potential
effect of ambiguous alignment portions, which were
104
masked and more or less rigorously removed by
the programs Aliscore and Gblocks (see Jörger et
al., 2010 for details). The topology showing best
likelihood resulting from Jörger et al. (2010) rejected
all traditional hypotheses on the origin of Acochlidia,
but indicate a pulmonate relationship of Acochlidia. In
particular, tree hypotheses were considered as robust
and reliable enough to propose a reclassification of
Euthyneura, abandoning the taxon name and concept
of Opisthobranchia.
The present paper combines results of Jörger et al.
(2010), Dinapoli & Klussmann-Kolb (2010), Dinapoli
et al. (2011) and some preliminary data on the origin
of Rhodopemorpha (see Wilson et al., 2010), and
reviews and discusses the status of Opisthobranchia
in the light of improving data sets and analytical
methods. Finally, it gives some examples how new
phylogenetic hypotheses affect old paradigms on
opisthobranch evolution, and recommends facing the
consequences of changing concepts.
Challenging the Opisthobranchia concept
Combining the results on the origin of Acochlidia
by Jörger et al. (2010) with a preliminary analysis
on the origin of Rhodopemorpha by Wilson et al.
(2010) by hand shows a consensus topology (Fig. 1)
that radically differs from traditional heterobranch
classifications. Monophyletic Rhodopemorpha
cluster among basal, shelled lower heterobranchs
with high support; thus, based on molecular data,
Rhodopemorpha are preliminary not related to any of
the euthyneuran taxa or even to dorid nudibranchs as
was suspected based on morphological data before.
The Opisthobranchia are polyphyletic: Acteonoidea
plus Rissoelloidea is the sister to Euthyneura, with
Nudipleura as first euthyneuran offshoot. Pulmonates
in a traditional sense are paraphyletic, including the
“opisthobranch” clades Sacoglossa and Acochlidia,
and the potential lower heterobranchs Glacidorbis and
Pyramidellidae, and thus were called Panpulmonata
by Jörger et al. (2010). The remaining opisthobranchs
form a clade called Euopisthobranchia by Jörger et
al. (2010). Several, but not all of these nodes (Fig 1;
see Jörger et al., 2010) are robustly supported and the
topologies slightly vary according to different analyses
and parameters. Nevertheless, Opisthobranchia are
not recovered monophyletic under any circumstances.
In particular, worm-like sluggish opisthobranch taxa
undoubtedly have independent origins and thus
structural, functional and biological similarities
evolved convergently due to selective pressure in
an extreme habitat (Jörger et al., 2010, Schrödl &
Neusser, 2010, Wilson et al., 2010). Bootstrap support
and posterior probability values are high for most
of the morphologically well-defined opisthobranch
and pulmonate subclades usually treated as
superfamilies or (sub)orders (collapsed to terminal
taxa in Fig 1). Excluding the historically enigmatic
Rhodopemorpha and Acteonoidea conceptually still
results in paraphyletic Opisthobranchia at best, with
Nudipleura as sister to all other euthyneurans, and
both Sacoglossa and Acochlidia clustering among
pulmonate taxa. Constraining the analyses of Jörger
et al. (2010) towards monophyletic Opisthobranchia
was highly significantly rejected based on their data.
Excluding Acochlidia or Sacoglossa or both from an
Opisthobranchia concept still does not render them
monophyletic. Standard molecular markers clearly
reject the monophyly of Opisthobranchia under
any historic or reasonable taxon definition, and the
topology (Fig. 1) differs from any morphology-based
classifications, apomorphy-based reconstructions
and, in particular, cladistic analyses that, thus, all
were misled.
New trees, new truths?
By showing the non-monophyly of Euthyneura,
Opisthobranchia and Pulmonata in a traditional
sense, our standard marker based tree hypothesis
(Fig. 1) is consistent to most previous molecular
analyses available, regardless of using single genes,
combinations of nuclear and mitochondrial genes or
mitochondrial genomic data. More problematic than
showing the deficiency of traditional classifications,
however, is to present a convincing alternative: data
sets, methods used and resulting topologies may
greatly differ depending on the data used and there
is no way of a direct numerical evaluation of how
reliably these trees reflect evolutionary history.
However, there is some evidence that the
design and performance of molecular studies on
heterobranchs evolved over time, and thus there is
hope that some of the latest topologies are superior
to previous ones. Early single gene analyses (e.g.
Thollesson, 1999a,b) were limited by still poor taxon
and character sampling, simplistic alignment tools
and parsimony as a single optimization criterion.
Studies using mitochondrial genes (Grande et al.
2004a,b) or mitochondrial genomes (Grande et al.,
2002, 2008, Medina et al., 2011) also were based
on inadequate and unrepresentative heterobranch
taxon sampling, the signal to noise ratio of markers
remains untested, and topologies still differ.
Supplementing the landmark studies on combined
18S and 28S rRNA genes by Vonnemann et al.
(2005) by further taxa and using the whole set of
what we now call “standard” genes of KlussmannKolb et al. (2008) and Dinapoli & Klussmann-Kolb
(2010), our current approaches (Jörger et al., 2010,
Wilson et al., 2010) use a multi-locus set of a truly
representative taxon sampling i.e. several lineages
of lower heterobranchs, all previously recognized or
suspected euthyneuran clades, and all the enigmatic
interstitial target taxa in question are included, plus
assumed relatives of Rhodopemorpha such as dorid
nudibranchs and several runcinids. In addition, the
few European acochlidian taxa used in previous
analyses (e.g. Vonnemann et al. 2005, Dinapoli &
Klussmann-Kolb, 2010) were shown to be highly
derived ones; especially Hedylopsis spiculifera,
but also the microhedylacean species Pontohedyle
milaschewitschii and Microhedyle glandulifera
showed long branches due to aberrantly evolved
loci in comparison to other, more slowly evolving
acochlidian species from other parts of the worlds
oceans (Jörger et al., 2010). Selecting a sufficient
number of basal and slow-evolving taxa from old
groups is clearly beneficial for minimizing branch
105
lengths and the effects of signal erosion (e.g. Wägele
& Mayer, 2007). On the data quality side, state of
the art procedures have been applied to minimize
errors and noise, i.e. sequences were checked by
BLAST searches and hypervariable regions of the
alignments removed by masking programs, and only
the most recent studies (e.g. Dinapoli & KlussmannKolb, 2010, Holznagel et al., 2010, Jörger et al.,
2010, Dayrat et al., 2011, Dinapoli et al., 2011,) used
both ML and Bayesian analyses, which is beneficial
to reveal and control for effects of different
evolutionary rates among lineages (e.g. Paps et al,
2009). While Holznagel et al. (2010) limited their
study on partial 28S of an incomplete panpulmonate
sampling, i.e. lacking Sacoglossa and Acochlidia,
the more representative and comprehensive standard
gene studies by Dinapoli & Klussmann-Kolb (2010)
and Jörger et al. (2010) seem to converge towards
a topology that is largely congruent to Fig. 1. We
thus assume that this topology will be fairly robust
to taxon addition. In particular, adding several
more species of Pyramidellidae to the standard
gene set, Dinapoli et al. (2011) already confirmed
the Pyramidellidae as part of a common clade
with Glacidorbis and Amphiboloidea. Göbbeler &
Klussmann-Kolb (2010) showed that the node of
Rissoelloidea and Acteonoidea is robust to adding
representatives of all acteonoidean families.
Despite all these efforts to optimize taxon
sampling, data quality, and alignment procedures,
neighbornet analyses by Dinapoli & Klussmann-Kolb
(2010) and Jörger et al. (2010) show a still high level
of conflict in the data, with split support for some
groups only. Since none of the well-supported nodes
in the tree is contradicted by the split analyses, we
do not interpret this as general evidence against our
tree but as a warning that the power of our standard
marker set for resolving heterobranch evolution has its
limitations. The topology shown herein (Fig. 1) needs
to be tested and refined by a truly independent set
of molecular markers showing a high signal to noise
ratio and minimizing the risk of alignment artefacts,
i.e. conservative, protein coding nuclear genes.
106
Violating morphology?
Our phylogenetic consensus hypothesis (Fig.
1) is based on a large and representative taxon
sampling, and on alignments of several thousands
of nucleotides; its major weakness is due to just 4
- and always the same - “standard genes” involved.
However, most of the traditionally accepted
heterobranch taxa on order or family level such as
Nudipleura, Acochlidia, Sacoglossa, Eupulmonata
and Ellobioidea were recovered as robustly supported
lineages. These molecular results are congruent with
morphology-based ideas, and thus are likely to
represent the evolutionary history. This also implies
that both morphology-based inference and standard
genes are informative at least at these levels. What
remains problematic are the interrelationships
between such major clades that have just poorly
supported and sometimes incongruent trees based
on standard markers. There is no doubt that much
of the conflict with previous morphology-based
hypotheses (e.g. Wägele & Klussmann-Kolb,
2005 as the most comprehensive one) is due to
misconceptions that based on misinterpretations of
homology and on extreme levels of homoplasy in the
latter, as already suspected by Gosliner (1981) and
Gosliner & Ghiselin (1984). The best examples refer
to mesopsammic, convergently evolved worm-like
taxa (Fig. 1) all showing a similar set of reductions
and innovations (e.g. Jörger et al., 2010, Schrödl
& Neusser, 2010), that are obviously adaptive to
their special habitat. Moreover, at present, we are
not able to present any conspicuous apomorphies
for the recently established clades, except for
Euopisthobranchia having evolved an oesophageal/
gizzard cuticle (Jörger et al., 2010). Morphology
thus has to be re-examined carefully and a priori
homology assumptions might have to be changed
according to a posteriori relationships unravelled.
On the other hand, even some of the most intriguing
relationships proposed by recent molecular analyses
(Dinapoli & Klussmann-Kolb, 2010; 2011; Jörger
et al., 2010) may fit within a morphological
framework. Glacidorbis clusters within pulmonates,
„Lower heterobranchs“
i l di Rhodopemorpha
including
Rh d
h
Rissoelloidea
?
Acteonoidea
Nudipleura
Diauly
Umbraculoidea
Runcinacea
Cephalaspidea s.s.
Anaspidea
p
?
Pteropoda
Monauly
Siphonarioidea
Sacoglossa
Glacidorboidea
Amphiboloidea
Pyramidellidae
Hygrophila
Acochlidia
Eupulmonata
Figure 2:
Evolution of “opisthobranchs”. Taxa with interstitial members are framed in red; mesopsammic habitat is basal in Acochlidia and possibly
Rhodopemorpha only; meiofaunal subclades, all more or less vermiform and showing an array of further adaptations, thus evolved many times
independently among Heterobranchia. Taxa with at least one secure pentaganglionate stage known in at least a single species (see Dayrat & Tillie,r
2000) are marked red; the only regularly pentaganglionate higher taxa may be Rhodopemorpha (juveniles only of Rhodope, adults of Helminthope)
and Acteonoidea (adult). Stem lineages of taxa showing monaulic reproductive systems are colored black, those having androdiaulic (including
triaulic) conditions are green; clades with mixed states are broken black/green, and clades with just exceptional and/or non-basal androdiaulic taxa
are dotted black/green. Note that it is parsimonious to assume that monauly evolved in the common, tectipleuran ancestor of Euopisthobranchia
and Panpulmonata. If so, true androdiauly (gonoducts split into oviduct and vas deferens proximal to the female gland mass) re-evolved in the stem
lineages of Sacoglossa, Glacidorboidea and within several other panpulmonate subclades. Also note that a variety of structurally differing monaulic
and diaulic conditions occur and that different authors use different terms; e.g. the special androdiaulic condition occurring in some acochlidians
is called monaulic by Valdés et al. (2010). In the light of novel phylogenetic hypotheses, the characters and evolution of heterobranchs need to be
re-examined in much greater depth.
i.e. as sister of Amphiboloidea, as suggested by
Ponder (1986), rather than being related with
lower heterobranchs as proposed by Haszprunar
(1985, 1988). The Pyramidellidae sensu stricto,
(i.e. all those Pyramidelloidea having a buccal
stylet rather than a complex jaw apparatus as in
Murchisonellidae) is an integral part of Euthyneura
even when comparing mitochondrial genomes
(Grande et al., 2008). This placement is supported
by central nervous features such as the possession
of giant nerve cells and a rhinophoral ganglion (see
Huber, 1993). Siphonarian intertidal (or even fully
marine) limpets were suggested to be opisthobranchs
(Haller, 1892) or most basal pulmonates based on
their morphology (Hyman, 1967), which fits with
their position as early panpulmonate descendants
of an opisthobranch grade. As discussed by Jörger
et al. (2010), morphological features usually
suggested to be synapomorphic for pulmonates
are either plesiomorphic, poorly explored, or of
limited significance. Even more straightforward,
accepting the proposed homology of the pulmonate
procerebrum and opisthobranch rhinophoral ganglia
(Haszprunar, 1988) that has received increasing
evidence from results of several microanatomical
studies (e.g. Huber, 1993, Neusser et al. 2007),
there is not a single putative synapomorphy left for
Opisthobranchia (Jörger et al., 2010).
107
Summing up, it is the absence of contradiction,
rather than unambiguous support, which makes the
novel euthyneuran phylogenetic hypothesis presented
by Jörger et al. (2010) and herein alluring. Still, the
monophyly of Pulmonata and Opisthobranchia are
clearly rejected by current knowledge (Fig. 1) and this
fact cannot be longer ignored.
Consequences
Accepting the core topology presented here (Fig.
1), or just parts of it, has dramatic consequences for
opisthobranch (and pulmonate) research.
First, neither “Opisthobranchia” nor “Pulmonata”
can be retained as monophyletic taxa and thus
have to be abandoned from our thinking and the
literature. A reclassification has been proposed
by Jörger et al. (2010) recently, modifying old
names according to new concepts, i.e. Nudipleura
as sister to a clade composed of Euopisthobranchia
plus Panpulmonata; the latter, well-supported clade
(Fig. 1) is named Tectipleura herein. In particular,
polyphyletic “Opisthobranchia” do not even form a
grade that can be characterized by any conspicuous
set of plesiomorphies. Traditional “Opisthobranchia”
thus are nothing else than an artificial assemblage
of usually marine slugs or snails with limpet-like,
bivalved or bubble shells showing tendencies of
reduction or internalization, having a more or less
detorted and externally bilateral symmetrical body
with usually at least one pair of head tentacles or a
head shield, including many exceptions. Rather than
having a phylogenetic or evolutionary or even merely
descriptive value, the “Opisthobranchia” concept is
of historical and –to many of us– emotional value
“only”.
Second, hypotheses on structures, functions or
any other features, homology, character polarity, and
evolution of opisthobranchs have to be reassessed in
the light of new phylogenetic evidence. Some of the
rampant parallelism assigned to Opisthobranchia is
actually attributable to a taxon misconception, while
108
even higher levels of homoplasy are indicated e.g.
by the independent origins of meiofaunal groups
showing an array of independently derived features
(e.g. Jörger et al., 2010, Schrödl & Neusser, 2010).
Intriguingly, basal Rhodopemorpha are one of the
few taxa supposedly showing a pentaganglionate
condition (in juveniles and/or adults), but, according
to Figs. 1 and 2, are not part of the Pentaganglionata
(=Euthyneura) sensu Haszprunar, a concept that
has been criticized before (Dayrat & Tillier, 2000).
Additionally, rhodopemorphs are euthyneurous
slugs that are not part of Euthyneura (Fig. 2).
The simple, monaulic condition of the reproductive
system was taken for granted to be plesiomorphic
for Opisthobranchia (e.g. Ghiselin, 1966, Gosliner,
1981, Valdés et al., 2010). Structurally more complex
diaulic conditions with separate male and female
gonoducts were thought to have evolved from such
a “primitive” level of organization, either as a
single event or in multiple convergence (Valdés et
al., 2010), with the condition in pulmonates unclear
(Wägele et al., 2008). Widening the taxonomic
focus and mapping monaulic and diaulic conditions
on our novel topology (Fig. 2) may question these
paradigms at least. It appears that (andro)diauly
evolved at least once already in the heterobranch
stemline and was plesiomorphically retained in
Nudipleura. Opisthobranch monauly thus evolved at
least once from a diaulic condition, possibly already
in the common ancestor of Euopisthobranchia and
Panpulmonata; monauly may be a synapomorphy of
Tectipleura. While basal clades of Euopisthobranchia
are monaulic, a few androdiaulic taxa exist
(“triaulic” Anidolyta, certain Ringicula spp; Valdés
et al., 2010), indicating secondary androdiauly. Also,
some secondary, more or less incomplete structural
and functional subdivisions of gonoducts may occur
in certain subtaxa, e.g. leading to a sometimes
called “oodiaulic” system in Anaspidea (Gosliner,
1994) or some cephalaspidean genera (Rudman &
Willan, 1998, Valdés et al., 2010). The situation
within panpulmonates is very complex showing
a mosaic of (primary or secondary) monaulic and
diaulic conditions in many major subgroups (Fig. 2),
implying much homoplasy involved. Androdiauly in
panpulmonates is structurally heterogeneous, e.g.
the vas deferens may split off the hermaphroditic
duct in a proximal (“true androdiauly”) or in more
distal position (“special androdiauly”, e.g. of some
Acochlidia), and may run freely in the body cavity
or in association to the body wall (as a “sunken”
or “closed” sperm groove) (e.g., see Hubendick,
1978; Golding et al., 2008; Schrödl & Neusser,
2010). Complex evolutionary scenarios proposed
by Visser (1977, 1988) trusted on a direct descent
of pulmonates from prosobranch ancestors that is,
however, rejected by all modern phylogenetic results.
The actual variation, homology and evolution of
heterobranch genital systems clearly merit detailed
comparative and integrative exploration. Even more
fundamentally changing our view, rather than being
a “crown group” the opisthobranchs including the
diverse Nudipleura and Euopisthobranchia now may
be considered as just moderately species rich and
successful early offshoots of the panpulmonate stem
line, leading to much higher ecological and species
diversity therein (Fig. 1).
Third, and of practical importance, in future
studies on traditional opisthobranch (or pulmonate)
taxa it is no longer tenable to just define and use
“Opisthobranchia” (or “Pulmonata”) as an ingroup,
as a taxon concept, or just as a point of reference,
without proving its monophyly by using an adequate
heterobranch taxon sampling. In simple words, there
is no more way to study opisthobranchs without
considering lower heterobranchs and pulmonates,
and vice versa. Instead, the traditionally isolated
research communities on basal heterobranch,
opisthobranch or pulmonate taxa have to recognize
that barriers are perceived rather than of a systematic
nature; the earlier we combine our knowledge and
efforts the better it is for furthering our branch of
science.
Fourth: Yes, we now advocate for renaming
the International Opisthobranch workshops as
Heterobranch workshops, to bring people together!
ACKNOWLEDGEMENTS
Warm thanks go to Jesús Troncoso, Vituco
Urgorri, Wily Díaz and all their helpers for organising
the 3rd International Workshop on Opisthobranchs
in Vigo, and for their efforts in putting together
this special volume. This study combines research
financed by the Volkswagen Foundation (to KMJ),
Scripps Institution of Oceanography (NGW), and the
DFG projects SCHR667/3,4 (to MS) and KL 1303/4
(to AKK). AKK is also supported by the LOEWEinitiative of the Hessian ministry of science through
the Biodiversity and Climate Research Centre. Heike
Wägele (Bonn) and Gerhard Haszprunar (Munich) are
thanked for many helpful discussions.
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Thalassas, 27 (2): 113-119
TIME FOR SEX CHANGE! 3D-RECONSTRUCTION OF THE
COPULATORY SYSTEM OF THE ’APHALLIC‘
Hedylopsis ballantinei (GASTROPODA, ACOCHLIDIA)
KOHNERT P, NEUSSER TP, JÖRGER KM & SCHRÖDL M
Key words: Mollusca, Panpulmonata, morphology, hypodermal injection, penial stylet, protandry, sequential hermaphroditism.
ABSTRACT
Within hedylopsacean acochlidians an
evolutionary trait from a simple unarmed copulatory
system towards complex hypodermal injection
systems was recognized. This culminates in a
large, trap-like spiny rapto-penis of several limnic
Acochlidiidae having a sperm injection stylet plus
an additional injection system with an accessory
gland. The only exception was the mesopsammic
hedylopsacean species Hedylopsis ballantinei
Sommerfeldt & Schrödl, 2005, since it was assumed
to be aphallic. Specimens with mature autosperm
and oogonia in the hermaphroditic gonad showed no
trace of any male copulatory organs. Sperm transfer
via spermatophores was thus suggested, as known
to occur in the generally aphallic microhedylaceans.
The present study re-examines several series of
semithin sections used for the original description.
Additionally, one specimen of H. ballantinei was
Bavarian State Collection of Zoology. Münchhausenstr.
21, D-81247 Munich, Germany.
Email: [email protected], [email protected], [email protected], [email protected]
newly collected near the type locality in the Red Sea.
It is externally identical with but smaller than the
original specimens. The specimen was embedded
into Spurr’s resin and serially cut into semithin
histological sections. Reproductive systems were
compared in detail and that of a specimen in the
male phase was 3-dimensionally reconstructed
using AMIRA software. The copulatory organs
comprise the posterior-leading vas deferens passing
into a voluminous tubular prostate, a presumable
paraprostate and a bipartite penis with a large apical,
hollow penial stylet and with a cuticular, solid thorn
on top of the basal swelling. As already known
for H. spiculifera (Kowalevsky, 1901), its European
sister species, H. ballantinei thus is a sequential
hermaphrodite with sex change. The male phase
precedes the female one, in which male copulatory
organs completely disappear. Sperm transfer is likely
by hypodermal injection. Hedylopsis ballantinei in
the male phase has an external sperm groove, while
specimens in the female phase possess a ciliary field;
the latter may have a function related to building or
placing the egg mass. Hedylopsis ballantinei now
fits well with evolutionary traits observed within
other hedylopsacean acochlidians known in detail.
113
Figure 1:
Schematic overview of the male cephalic copulatory organs with associated glands of Hedylopsis ballantinei. Abbreviations: bs, basal swelling; ed,
ejaculatory duct; mgo, male gonopore; p, penis; ppd, paraprostatic duct; ppr, paraprostate; pr, prostate; ps, penial sheath; pst, hollow penial stylet;
sg, external sperm groove; th, solid thorn; ugm, unidentified glandular mass; vdp, posterior-leading vas deferens. Not to scale.
INTRODUCTION
Most recently, opisthobranch gastropods were
shown to be an artificial assemblage, with the
traditional order Acochlidia clustering within a (pan)
pulmonate relationship (Jörger et al., 2010; Schrödl
et al., this volume pags. 101-112). Both molecular
and morphology-based phylogenetic analyses (Jörger
et al., 2010; Schrödl & Neusser, 2010) indicate a
basal acochlidian split into generally regressive,
meiofaunal Microhedylacea (Neusser et al., 2009)
and morphologically and ecologically more variable
Hedylopsacea, including marine, brackish water and
limnic species of variable body sizes (e.g. Neusser
& Schrödl, 2007, 2009; Brenzinger et al., 2011).
Within hedylopsacean acochlidians an evolutionary
trait from a simple, unarmed copulatory system
towards complex hypodermal injection systems
was recognized (Schrödl & Neusser, 2010). This
culminates in the large, trap-like spiny rapto-penis
of several limnic Acochlidiidae, having a sperm
114
injection stylet plus an additional injection system
with an accessory gland (Haase & Wawra, 1996).
The only exception in this evolutionary scenario of
evolving a more and more complex and probably
violent copulatory apparatus was the mesopsammic
hedylopsacean species Hedylopsis ballantinei
Sommerfeldt & Schrödl, 2005, since it was assumed
to be aphallic. The few specimens available had
mature autosperm and oogonia in the hermaphroditic
gonad, but showed no trace of any copulatory organs
(Sommerfeldt & Schrödl, 2005). Sperm transfer via
spermatophores was thus suggested, as known to
occur in the generally aphallic microhedylaceans.
The present study examines old and new material of
different-sized H. ballantinei from serial histological
sections for the presence of reproductive organs.
Male copulatory organs were identified, labeled
and 3-dimensionally reconstructed using AMIRA
software, and compared to other hedylopsacean
copulatory systems.
TIME FOR SEX CHANGE! 3D-RECONSTRUCTION OF THE COPULATORY SYSTEM OF THE ’APHALLIC‘
One specimen of Hedylopsis ballantinei was
newly collected approx. 600 m north of the type
locality (Inmo Reef) in Mashraba (28°29`42``
N, 34°31`04`` E), Dahab, Egypt in August 2009.
A sample of coarse coral sand was obtained by
snorkeling from 6 m depth by night. The specimen
was extracted from the sand sample according
to the method described by Schrödl (2006). The
specimen was relaxed with isotonic MgCl 2-solution
and was preserved in 4 % glutardialdehyde buffered
in 0.2 M sodium cacodylate (0.1 M NaCl and
0.35 M sucrose, pH 7.2). Following a post-fixation
in buffered 1 % OsO 4 for 1.5 h in the dark, the
specimen was decalcified in 1 % ascorbic acid
overnight and dehydrated in an acetone series (30,
50, 70, 90, 100 %). For semithin sectioning the
specimen was embedded in Spurr’s low viscosity
resin (Spurr, 1969) and a series of ribboned serial
semithin sections of 1.5 μm thickness was prepared
using a diamond knife (Histo Jumbo, Diatome,
Biel, Switzerland) and contact cement on the lower
cutting edge to form ribbons (Ruthensteiner, 2008).
Finally, the sections were stained with methyleneazure II (Richardson et al., 1960) and were deposited
at the Mollusca Section of the Bavarian State
Collection of Zoology (ZSM), Germany (ZSM
Mol 20100856). Additionally, we (re-) examined
five series of serial semithin sections (2 μm) of
Hedylopsis ballantinei which were available at the
ZSM by light microscopy: ZSM Mol 20100855,
ZSM Mol 20004766/1, ZSM Mol 20004767, ZSM
Mol 20004768 and ZSM Mol 20004769. The series
N° 20100855 revealed H. ballantinei to possess
mature male copulatory organs. Digital photographs
of every slice of the latter series were taken with a
CCD microscope camera (Spot Insight, Diagnostic
Instruments, Sterling Heights, USA) mounted on
a DMB-RBE microscope (Leica Microsystems,
Wetzlar, Germany). The image resolution was
reduced to 50 % and images were contrast enhanced,
unsharp masked and converted to 8bit greyscale
format with standard image editing software. A
detailed computer-based 3D-reconstruction of the
body surface and the male reproductive system
was performed using the software AMIRA 5.2.2
(Visage Imaging GmbH, Germany) as outlined by
Ruthensteiner (2008).
RESULTS
The re-examination of the semithin section
series used for the original description of Hedylopsis
ballantinei (see Sommerfeldt & Schrödl, 2005)
and for the examination of the excretory system
(Fahrner & Haszprunar, 2002, as Hedylopsis sp.),
did not provide new data on the male reproductive
system. The newly collected specimen was in the
female phase with mature female reproductive
organs, but lacking any male copulatory organs. In
contrast, the examination of a series of semi- and
ultrathin sections (ZSM Mol 20100855) showed
a male specimen of H. ballantinei with mature
complex copulatory organs. The 3D reconstruction
by Amira and the following description of the male
genital system of H. ballantinei is based on series
N° 20100855.
Hedylopsis ballantinei is a sequential, protandric
hermaphrodite with an external sperm groove (Figs.
1; 2A,B) in the male phase and a ciliary field in the
female phase. The external sperm groove connects
the posterior reproductive system from the female
gonopore (Fig. 2D) to the male gonopore (Fig. 1) and
the cephalic male copulatory organs (Figs. 1; 2A-C).
The latter include a large bipartite penis with an
apical hollow stylet, a very voluminous prostate, a
potential paraprostate and an accessory gland (Figs.
1; 2C) with unknown function and homology.
The posterior-leading vas deferens (Figs. 1;
2A,B) leads from the male genital opening (Fig. 1)
which is situated at the base of the right rhinophore,
to the tubular, glandular prostate (Figs. 1; 2A,B,F).
The ejaculatory duct (Fig. 1) emerges from the latter
and enters the muscular penis (Figs. 1; 2A-C). A
second glandular mass, the sac-like paraprostate
115
Figure 2:
3D-reconstruction and histological semithin sections of the male reproductive system of Hedylopsis ballantinei. A, Hermaphroditic reproductive
system (ventral view); B, Male cephalic copulatory organs (right view); C, Penis and basal swelling with glands and armature (anterior view); D,
Body with ovotestis and female glands (right anterolateral view); E, Penis, penial stylet and basal thorn; F, Ovotestis, prostate and female glands.
Abbreviations: bs, basal swelling; dg, digestive gland; f, foot; fgl, female glands; fgo, female gonopore; lt, labial tentacle; ov, ovotestis; p, penis; pd,
prostatic duct; plg, pleural ganglion; ppd, paraprostatic duct; ppr, paraprostate; pr, prostate; ps, penial sheath; pst, hollow penial stylet; sg, external
sperm groove; th, solid thorn; ugm, unidentified glandular mass; vdp, posterior-leading vas deferens; vh, visceral hump.
116
(Figs. 1; 2A-C,E), is much smaller than the prostate
and connected to the penis via the paraprostatic
duct (Figs. 1; 2C). The latter enters the penis in
the upper part and joins the ejaculatory duct.
Together they discharge at the top of the penial
papilla into a curved, hollow penial stylet (Figs.
1; 2A,C,E) of approx. 160 μm length. A muscular
basal swelling with a solid thorn of approx. 40 μm
(Figs. 1; 2A,C,E) is attached to the base of the penis.
Near the muscular penis an additional, unidentified
glandular mass (Figs. 1; 2B,C,E) with yet unknown
function was detected. The bipartite penis and the
unidentified glandular mass are surrounded by the
thin-walled penial sheath (Figs. 1; 2E).
DISCUSSION
Among hedylopsacean acochlidians, H.
ballantinei was exotic in lacking any detectable
cephalic male reproductive organs. The presence
of mature autosperm and egg cells in the
hermaphroditic gonad of aphallic specimens
led Sommerfeldt & Schrödl (2005) to assume
that H. ballantinei is an aphallic hermaphrodite
species rather than a sequential hermaphrodite
as Hedylopsis spiculifera. However, our results
show a specimen of H. ballantinei having
complex male reproductive organs, while others
do not possess any. We thus conclude that H.
ballantinei is a sequential hermaphrodite with a
male, phallic phase preceding a female, aphallic
phase, just as it was described for H. spiculifera
by Wawra (1989). The function, if any, of testis
remainders in aphallic, early (?) female stages
is unknown. All hedylopsacean species known
to date thus have copulatory organs, in contrast
to microhedylaceans that are all aphallic during
their entire ontogeny (e.g. Neusser et al., 2009).
The external sperm groove of Hedylopsis in the
male phase is likely to transform into the ciliary
field that was observed in the female phase of
specimens of H. ballantinei by Sommerfeldt &
Schrödl (2005); a function related to handling the
egg mass can be inferred.
Sequential hermaphroditism with complete
reduction of copulatory organs occur in some,
but not all hedylopsacean clades, i.e. in the genus
Hedylopsis, Strubellia, and possibly in Tantulum
(Wawra, 1989; Neusser & Schrödl, 2007; Brenzinger
et al., 2011). In contrast, Pseudunela, Acochlidium and
Palliohedyle may be protandric but then simultaneous
hermaphrodites during most of their ontogeny
(Bücking, 1933; Haynes & Kenchington, 1991;
Wawra, 1980; Neusser & Schrödl, 2009; Neusser et
al., 2009). Mapping this feature on an acochlidian
consensus tree (Neusser et al., 2009) reveals an
ambiguous scenario. Possibly, hedylopsaceans are
sequential hermaphrodites either ancestrally or
evolved ontogenetic resorption of copulatory systems
after the offshoot of Tantulum from the stemline, with
re-evolution of simultaneous hermaphroditism in
Pseudunela and the common ancestor of Acochlidium
and Palliohedyle.
The anterior male copulatory system of H.
ballantinei is quite complex, resembling that of
its congener H. spiculifera in having an external
sperm groove leading to a cephalic posteriorleading vas deferens with a well-developed prostate
and a muscular penial papilla tipped with a hollow
stylet. The dimensions of the penial stylets cannot
be compared due to lacking data on the stylet
length of H. spiculifera. Obviously, sperm is
transferred to the mate via injection rather than
via spermatophores as assumed originally for H.
ballantinei (see Sommerfeldt & Schrödl, 2005). In
absence of any allosperm receptacles (Sommerfeldt
& Schrödl, 2005), hypodermal injection is likely.
Imprecise sperm transfer into the body cavity was
observed from H. spiculifera by Wawra (1989)
who detected a penial stylet in the visceral sac
of a mature female specimen. In both species the
penis is bipartite having a basal swelling with a
solid, cuticular thorn. The copulatory organs of
H. ballantinei differ from those of H. spiculifera
by the presence of a rather well-developed gland,
a putative paraprostate, which connects through
a duct to the ejaculatory duct within the penis.
117
Table 1:
Comparison of the male genital system within Hedylopsis. (? = no data available).
Data source
Hedylopsis
spiculifera
(Kowalevsky,
1901)
Wawra (1989)
Type of
hermaphroditism
Hedylopsis ballantinei Sommerfeldt & Schrödl,
2005
Sommerfeldt &
Schrödl (2005)
present study
sequential,
protandric
simultaneous
sequential, protandric
Complex,
cephalic male
copulatory
organs
penis with
hollow stylet
and basal thorn,
prostate, penial
gland of
unknown
function and
homology
absent
large bipartite penis with
apical hollow penial
stylet (approx. 160 μm)
and basal thorn (approx.
40 μm), voluminous
prostate, potential
paraprostate, plus
accessory gland of
unknown function and
homology
Sperm transfer
via
hypodermic
injection
spermatophore
hypodermic injection
for handling
spermatophore
probably involved in egg
mass deposition
Function of ciliary ?
field
Specimens of H. spiculifera have a small “penial
gland” in a corresponding location that, however,
opens separately at the base of the penial stylet.
A comparison of the male reproductive features
within Hedylopsis is given in Table 1.
Potentially homologous, more elaborate
paraprostatic systems present in higher
hedylopsaceans (Neusser & Schrödl, 2009; Neusser
et al., 2009; Brenzinger et al., 2011) are separated
from the ejaculatory duct and exit via own stylets
on the tip of the basal swelling that is developed into
a larger, so-called basal finger (according to Haase
& Wawra, 1996). The copulatory system found in
H. ballantinei thus represents a formerly unknown,
intermediate condition in hedylopsaceans and is in
line with the idea of progressively evolving more and
more elaborate copulatory organs with various glands
and injection systems (Neusser et al., 2009; Schrödl
& Neusser, 2010).
118
CONCLUSIONS
1. Hedylopsis ballantinei is a sequential protandric
hermaphrodite with sex change.
2. H. ballantinei has a large and complex cephalic
copulatory organ with an apical hollow stylet, a
solid thorn and two accessory gland systems, all
of which completely disappear in the early female
phase. Some male parts of the gonad, however, may
still persist after the loss of the copulatory organs.
3. The presence of an apical penial stylet and a basal
thorn resembles that of Hedylopsis spiculifera;
but the arrangement of glands is unique.
4. As a phallic species transferring sperm via
hypodermic impregnation and lacking any
allosperm receptacles, H. ballantinei now much
better resembles its Mediterranean/ eastern
Atlantic sister species H. spiculifera, and fits
well with evolutionary traits observed within
hedylopsacean acochlidians.
ACKNOWLEDGEMENTS
We thank the organizing team of the 3rd
International Workshop on Opisthobranchs in Vigo.
We are grateful to Christian Alter at the RSEC (Red
Sea Environmental Center) for support during field
work and collecting permits. This study was financed
by DFG projects (SCHR667/3,4) to MS, and by a PhD
grant by the Volkswagen Foundation to KJ. Amira
software was supported by the GeoBio Center (LMU
Munich). Bastian Brenzinger (ZSM) and an unknown
referee gave valuable comments on the manuscript.
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Sommerfeldt N, Schrödl M (2005). Microanatomy of
Hedylopsis ballantinei, a new interstitial acochlidian
gastropod from the Red Sea, and its significance for
phylogeny. Journal of Molluscan Studies, 71: 153-165.
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medium for electron microscopy. Journal of
Ultrastructural Research, 26: 31-43.
Wawra E (1980). Acochlidium bayerfehlmanni spec. nov.,
(Gastropoda: Opisthobranchia: Acochlidiacea) from
Palau Islands. Veliger, 22: 215-220.
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119
Thalassas, 27 (2): 121-154
MOLECULAR PHYLOGENY OF THE EUTHYNEURA
(MOLLUSCA, GASTROPODA) WITH SPECIAL FOCUS
ON OPISTHOBRANCHIA AS A FRAMEWORK FOR
RECONSTRUCTION OF EVOLUTION OF DIET
KATRIN GÖBBELER(1,*) & ANNETTE KLUSSMANN-KOLB(1)
Key words: character evolution, BayesTraits, molecular systematics, diet, herbivory, Euthyneura
ABSTRACT
The Opisthobranchia comprise a group of highly
specialized gastropods with uncertain systematic
affinities. Moreover, monophyly of the whole clade
has been repeatedly questioned. The present study
presents the currently most extensive analyses on
opisthobranch phylogeny including 58 species from
all major subgroups. A combination of four gene
markers as well as diverse molecular systematic
analytical approaches are applied in order to shed new
light on the evolution of this taxon. Special emphasis
is given to the reconstruction of ancestral diet
preferences since extant Opisthobranchia feed on a
variety of different food items and the development of
dietary specialization is supposed to be important for
the evolution of these enigmatic marine gastropods.
(1) Institute for Ecology, Evolution and Diversity, GoetheUniversity Frankfurt, Siesmayerstrasse 70, 60054 Frankfurt
am Main, Germany
*Current address: Department of Integrative Biology,
University of Colorado Denver, P.O. Box 173364, Denver, CO
80217, USA
Based on the presented data monophyly
of Opisthobranchia is clearly rejected. However,
monophyly of the Euthyneura (comprising
Opisthobranchia and Pulmonata) is supported.
Furthermore, monophyly of most subgroups is
revealed. The Runcinacea are found as a separate
clade clustering apart from the remaining
Cephalaspidea, the taxon in which they have been
formerly classified. Furthermore, Aplysiomorpha
and Pteropoda are recovered as a monophyletic
clade, while the Aplysiomorpha are found to be
paraphyletic due to the position of a single taxon.
In addition, Cylindrobullida are revealed as part of
the sacoglossan subclade Oxynoacea denying their
current separate status. The enigmatic Acochlidiacea
are revealed as sister group to Eupulmonata.
Ancestral diet preferences are reconstructed for
monophyletic Euthyneura and all main subclades since
polyphyly of Opisthobranchia impeded reconstruction
for this clade. Herbivory is found as the most likely
ancestral diet of Euthyneura while carnivory probably
evolved several times independently in different
clades.
121
KATRIN GÖBBELER & ANNETTE KLUSSMANN-KOLB
Figure 1:
Bayesian inference phylogram of the phylogenetic analyses (concatenated alignment of 18S rDNA, 28S rDNA, 16S rDNA and CO1), 50% majority
rule consensus tree. Posterior probabilities are provided at the nodes; only support values above 0.5 are given. Taxonomic classifications (following
Bouchet and Rocroi, 2005) are indicated and shaded on the right side (“lower Heterobranchia” = white; Opisthobranchia = light grey; Pulmontata
= dark grey). The branch leading to the nudipleuran Dexiarchia was shortened by about 50% to allow better visibility.
122
MOLECULAR PHYLOGENY OF THE EUTHYNEURA (MOLLUSCA, GASTROPODA)
WITH SPECIAL FOCUS ON OPISTHOBRANCHIA AS A FRAMEWORK FOR RECONSTRUCTION OF EVOLUTION OF DIET
INTRODUCTION
The Opisthobranchia are a group of gastropods comprising morphologically diversified species which are distributed globally in all marine
habitats. They are composed of about 6000 species (Wägele et al., 2008) currently divided into
nine main clades: Cephalaspidea, Thecosomata,
Gymnosomata, Aplysiomorpha, Acochlidiacea,
Sacoglossa, Cylindrobullida, Umbraculida and
Nudipleura (Bouchet and Rocroi, 2005). Monophyly
of these clades has been well supported in molecular
systematic studies (Wägele et al., 2003; Grande et
al., 2004a, b; Vonnemann et al., 2005; KlussmannKolb and Dinapoli, 2006; Klussmann-Kolb et al.,
2008; Dinapoli and Klussmann-Kolb, 2010; Jörger
et al., 2010). Furthermore, the pelagic Thecosomata
and Gymnosomata have been revealed as sister
groups forming the Pteropoda (Klussmann-Kolb and
Dinapoli, 2006).
The main evolutionary trend in Opisthobranchia
is reduction or even loss of the shell (Grande et al.,
2004a) accompanied by development of diverse
defensive strategies (Wägele and Klussmann-Kolb,
2005). Radiation of opisthobranchs has lead to
parallelism and convergence of morphological
characters (Gosliner and Ghiselin, 1984; Gosliner,
1985, 1991) hampering morphology based
classification. Thus, phylogenetic hypotheses on
Opisthobranchia vary based on morphological
considerations (Schmekel, 1985; Bieler, 1992;
Salvini-Plawen and Steiner, 1996; Dayrat and Tillier,
2002; Mikkelsen, 2002; Wägele and KlussmannKolb, 2005). Moreover, molecular phylogenetic
analyses reveal contradictory classifications as well
(Thollesson, 1999; Dayrat et al., 2001; Grande et al.,
2004a, b; Vonnemann et al., 2005; Klussmann-Kolb
and Dinapoli, 2006; Klussmann-Kolb et al., 2008;
Dinapoli and Klussmann-Kolb, 2010; Jörger et al.,
2010) mainly due to differences in taxon sampling,
employed marker genes and outgroup determination.
Thus, a common solution and a robust phylogeny of
Opisthobranchia are still lacking.
Monophyly of the Opisthobranchia has been
challenged by several authors due to the lack
of proper synapomorphies (Salvini-Plawen
and Steiner, 1996; Ponder and Lindberg, 1997)
caused by “rampant parallelism” (Gosliner and
Ghiselin, 1984) in this taxon. Moreover, previous
phylogenetic analyses often failed to reveal
monophyly of this taxon both in morphology-based
studies (Dayrat and Tillier, 2002; Wägele and
Klussmann-Kolb, 2005) and molecular systematic
investigations (Thollesson, 1999; Dayrat et
al., 2001; Grande et al., 2004a, b; KlussmannKolb et al., 2008; Dinapoli and KlussmannKolb, 2010; Jörger et al., 2010). In a recent
study focusing on phylogeny and systematics of
Acochlidiacea, Jörger et. al (2010) propose the new
clade Euopisthobranchia uniting Umbraculida,
Aplysiomorpha, Cephalaspidea and Pteropoda.
This clade presents a “monophyletic remainder
of the (non-monophyletic) “Opisthobranchia” as
traditionally defined” (Jörger et al., 2010, p. 7).
Opisthobranchia are supposed to form a clade
with pulmonate gastropods called Euthyneura
(Spengel, 1881). Monophyly of this clade has been
detected in morphological (Ponder and Lindberg,
1997; Dayrat and Tillier, 2002) as well as molecular
systematic studies (Thollesson, 1999; Wade and
Mordan, 2000; Knudsen et al., 2006) while other
molecular systematic studies reveal paraphyly of
Euthyneura (Dayrat et al., 2001; Grande et al.,
2004b; Klussmann-Kolb et al., 2008; Dinapoli
and Klussmann-Kolb, 2010; Jörger et al., 2010).
Nevertheless, Thollesson (1999) as well as Jörger
et al. (2010) claimed the constant inclusion of both
pulmonate and opisthobranch taxa in phylogenetic
studies due to their possibly common origin. Thus,
erroneous monophyly of either clade based on
incomplete taxon sampling can be avoided. We
follow this request in the present investigation by
incorporating both opisthobranch and pulmonate
species in our analyses. Additionally, several “lower
heterobranch” taxa are included to test monophyly
of Euthyneura.
123
Figure 2:
Neighbour-net graph of the split decomposition analysis (concatenated alignment of 18S rDNA, 28S rDNA, 16S rDNA and CO1).
Taxonomic classification (according to Bouchet and Rocroi, 2005) indicated by braces.
124
A highly specialized and possibly crucial feature
for evolution in Opisthobranchia is represented by their
diverse diet (Thompson, 1976; Rudman and Willan,
1998; Mikkelsen, 2002; Wägele, 2004). Many potential
key characters for opisthobranch evolution are related
to diet and supposed to trigger exploration of new food
sources (Wägele, 2004). Some opisthobranch clades
feed on algae (Aplysiomorpha, Sacoglossa); others are
specialized on Porifera (Umbraculida), while diverse
carnivorous (Nudipleura) or even carnivorous or
herbivorous food items (Cephalaspidea) are preferred
in other groups. Some opisthobranch species exhibit
remarkable adaptations to a special source of food,
e.g. Nudibranchia living in mutualistic symbiosis
with photosynthetic dinoflagellates and sharing
metabolites (Burghardt et al., 2005) or Sacoglossa
incorporating chloroplasts of their algal food in their
own digestive gland and using metabolites (Rumpho
et al., 2000; Händeler et al., 2009). The evolution
of these highly specialized features is largely
unknown. Malaquias et al. (2009a) reconstructed the
ancestral diet of Cephalaspidea comprising diversely
specialized species, but up to now the ancestral diet
of the last common ancestor of the Opisthobranchia
remains a matter of debate. Haszprunar (1985)
claimed that carnivory is the plesiomorphic
condition due to diet preferences of the possibly
basal opisthobranch taxon Architectibranchia. On
the contrary, Mikkelsen (1996, 2002) argued that
herbivory was the ancestral state. Vermeij and
Lindberg (2000, p. 423) suggested that “feeding on
sessile invertebrates may be the plesiomorphic mode
of feeding from which herbivory arose in various
gastropod clades” (including Opisthobranchia).
However, specific dietary preferences are likely
the result of a complex interplay of phylogeny, prey
structure and habitat (Mikkelsen, 1996). Thus, it
is important to reconstruct the ancestral state in
order to gain new insights into the evolution of this
specialized character complex.
We attempt to close this gap of knowledge by
making use of the software BayesTraits (Pagel et al.,
2004) which is a powerful tool for the reconstruction
of ancestral character states applying a Bayesian
approach. For this purpose, we conducted a thorough
literature search on diet of Opisthobranchia to
enable reconstruction of ancestral preferences.
This reconstruction is based on the currently most
comprehensive molecular systematic study on
opisthobranch phylogeny covering all main subclades
in order to account for their interrelationships and
provide the framework for reconstruction of character
evolution.
Taxon sampling
The current study comprises a total of 86 taxa
with 58 Opisthobranchia covering all subclades.
Additionally 18 Pulmonata (including all main
subclades) and nine “lower Heterobranchia” (with
a special focus on the questionable opisthobranch
clade Acteonoidea) complement the taxon sampling.
The caenogastropod Littorina littorea was defined as
outgroup taxon.
Sequences were primarily taken from GenBank,
supplemented by some newly generated sequences
of crucial taxa. Specimens were collected worldwide
by hand, snorkeling, or scuba diving and preserved
in 80-100% ethanol. Origin of all taxa and accession
numbers of utilized sequences are summarized in
Table 1.
DNA extraction, PCR and sequencing
Genomic DNA was extracted from muscle tissue
via the DNeasy Tissue Kit (Qiagen, Hilden, Germany)
according to the animal tissues/spin-column protocol.
We amplified two nuclear (complete 18S rDNA
and partial 28S rDNA) and two mitochondrial (partial
16S rDNA and CO1) gene fragments, which were
sequenced in both directions. Primer sequences and
PCR-protocols are given in Göbbeler and KlussmannKolb (2010).
125
Figure 3:
Cladogram of the Baysian inference analysis (concatenated alignment of 18S rDNA, 28S rDNA, 16S rDNA and CO1; 50% majority rule consensus
tree). Dietary coding of species indicated as colour coded (carnivory = red, herbivory = green, unselective = yellow) squares before species names.
Results of reconstruction of character evolution mapped onto the tree coded as pie charts displaying color coded (carnivory = red, herbivory =
green, unselective = yellow) fractions of the diverse dietary types (inferred from posterior probabilities) . Taxonomic classification (following Bouchet
and Rocroi, 2005) provided at the right side, major clades are shaded..
126
PCR-products were purified from an agarose gel
using the QIAquick Gel Extraction Kit from Qiagen
(Hilden, Germany). Sequencing was performed using
a CEQ 2000 Beckmann Coulter capillary sequencer
at the scientific research lab in Frankfurt/Main.
Sequence alignment
Mafft version 6 (Katoh et al., 2005) was used
for alignment of sequences under the linsi-option
displaying one of the most accurate multiple sequence
alignment methods. The results were analysed with
Aliscore (Misof and Misof, 2009) to filter ambiguous
or randomly similar sites in the alignment which
were subsequently deleted from the alignment. The
maximal number of possible pairs was compared
and gaps were treated as ambiguous characters.
The single codon positions of the CO1-sequences
were analysed separately. Details about alignment
length and Aliscore results with excluded nucleotide
positions are summarized in Table 2.
Statistical tests
Several statistical tests were conducted on our
data after exclusion of ambiguous sites and prior to
phylogenetic analyses to estimate data quality and
survey the results.
The Incongruence Length Difference (ILD)
test (Farris et al., 1995) was used to examine the
significance of incongruence in our combined dataset.
This test is implemented in PAUP 4.0b10 (Swofford,
2002) as Partition Homogeneity test and was used to
check if the single gene markers provide a congruent
phylogenetic signal and can thus be concatenated
and analysed as a single dataset. We conducted 100
replicates of a heuristic search under the Maximum
Parsimony criterion.
Substitution saturation of the single datasets
was evaluated via the test by Xia et al. (2003) as
implemented in the software package DAMBE (Xia
and Xie, 2001).
The Approximately Unbiased (AU) test
(Shimodaira, 2002) was employed to test an
alternative tree topology enforcing monophyly of
the Opisthobranchia. Likelihoods were calculated for
each nucleotide position in PAUP 4.0b10 (Swofford,
2002) for the constrained and unconstrained topology
and subsequently compared in CONSEL version 0.1
(Shimodaira and Hasegawa, 2001) in order to obtain
p-values.
We investigated rate heterogeneity in the
sequences with a relative rate test using the software
k2WuLi (Wu and Li, 1985).
Phylogenetic analyses
The best fitting model of sequence evolution for
each gene partition (single codon positions of CO1
separately) was determined via MrModeltest 2.2
(Nylander, 2004) based on the Akaike information
criterion (AIC) prior to phylogenetic analyses.
Details about the determined models are provided
in Table 2.
Bayesian inference analysis was performed via
MrBayes 3.1.2 (Huelsenbeck and Ronquist, 2001)
using separate models of evolution for each gene
partition. Two separate runs of four chains each
(one cold, three heated) of a Metropolis – coupled
Markov chain Monte Carlo algorithm operated for
2,000,000 generations. Likelihoods converged slowly,
thus the first 15,000 trees were ignored as burn-in for
construction of the 50% majority rule consensus tree.
Posterior probabilities were calculated for each node,
a value of 0.95 and higher being considered as good
statistical support.
The result of this phylogenetic analysis was
reassessed by a split-decomposition analysis on
the concatenated alignment using SplitsTree 4.9.1
(Huson, 1998; Huson and Bryant, 2006). Split graphs
show networks of phylogenetic relationships revealing
conflicts in data sets. We constructed a neighbor-net
graph based on uncorrected p-distances.
127
Table 1: Information on taxon sampling and Genbank accession numbers. * = sequences generated for the current study
GenbankAccessionNumbers
Taxon
Family/Subfamily
Locality
18S
28S
16S
CO1
X91970
AJ488672
DQ093481
DQ093525
CAENOGASTROPODA
Littorinalittorea
Littorinidae
Genbank
LOWERHETEROBRANCHIA
Orbitestellasp.
Orbitestellidae
Genbank
EF489352
EF489377
EF489333
EF489397
Cimasp.
Cimidae
Genbank
FJ917206
FJ917228
FJ917260
FJ917279
Rissoellarissoaformis
Rissoellidae
Genbank
FJ917214
FJ917226
FJ917252
FJ917271
Acteontornatilis
Acteonidae
Genbank
GQ845182
GQ845183
GQ845177
GQ845190
GQ845172
Pupanitidula
Acteonidae
Genbank
GQ845185
GQ845179
GQ845192
GQ845173
Rictaxispunctocaelatus
Acteonidae
Genbank
GQ845186
EF489370
GQ845193
EF489393
Hydatinaphysis
Aplustridae
Genbank
AY427515
AY427480
EF489320
GQ845174
Micromeloundata
Aplustridae
Genbank
GQ845188
GQ845181
GQ845195
GQ845176
Bullinalineata
Bullinidae
Genbank
GQ845189
Ͳ
GQ845196
AY296847
ACTEONOIDEA
OPISTHOBRANCHIA
CEPHALASPIDEA
BULLOIDEA
Bullastriata
Bullidae
Genbank
DQ923472
DQ986683
DQ986632
DQ986566
Diaphanasp.
Diaphanidae
Genbank
DQ923455
EF489373
EF489325
EF489394
Toledoniaglobosa
Diaphanidae
Genbank
EF489350
EF489375
EF489327
EF489395
Haminoeahydatis
Haminoeidae
Genbank
AY427504
AY427468
EF489323
DQ238004
Atyscylindricus
Haminoeidae
Genbank
DQ923458
DQ927228
Ͳ
DQ974671
Smaragdinellasp.
Smaragdinellidae
Genbank
AJ224789
DQ927242
AF249257
AF249806
Scaphanderlignarius
Cylichnidae
Genbank
EF489348
EF489372
EF489324
DQ974663
Philineaperta
Philinidae
Genbank
DQ093438
DQ279988
DQ093482
AY345016
Odontoglajasp.
Aglajidae
Genbank
DQ923450
DQ927218
Ͳ
DQ974655
DIAPHANOIDEA
HAMINOEOIDEA
PHILINOIDEA
128
Philinopsispilsbryi
Aglajidae
Genbank
AY427509
AY427474
AM421840
AM421888
Sagaminopteron
psychedelicum
Gastropteridae
Genbank
AY427513
AY427478
AM421815
AM421856
Philinoglossapraelongata
Philinoglossidae
Genbank
AY427510
AY427475
Ͳ
Ͳ
Retusasp.
Retusidae
Genbank
AY427511
AY427476
Ͳ
DQ974679
Pyrunculussp.
Retusidae
Genbank
DQ923465
DQ927237
Ͳ
DQ974678
Runcinaafricana
Runcinidae
Genbank
DQ923473
DQ927240
Ͳ
DQ974680
Ilbiailbi
Ilbiidae
Australia,NSW
GU213047*
GU213052*
GU213043*
GU213057*
Akeridae
Genbank
AY427502
AY427466
AF156127
AF156143
Aplysiacalifornica
Aplysiidae
Genbank
AY039804
AY026366
AF192295
AF077759
Dolabriferadolabrifera
Aplysiidae
Genbank
DQ237960
DQ237973
AF156133
AF156149
Bursatellaleachii
Aplysiidae
Genbank
DQ237961
DQ237975
AF156130
AF156146
Dolabellaauricularia
Aplysiidae
Genbank
AY427503
AY427467
AF156132
AF156148
Stylocheiluslongicauda
Aplysiidae
Genbank
DQ237963
DQ237978
AF156140
AF156156
Petaliferapetalifera
Aplysiidae
Genbank
DQ237962
DQ237977
Ͳ
AY345020
Cavoliniauncinnata
Cavoliniidae
Genbank
DQ237964
DQ237983
Ͳ
DQ237997
Hyalocylisstriata
Cavoliniidae
Genbank
DQ237966
DQ237985
Ͳ
DQ237999
Cliopyramidata
Cavoliniidae
Genbank
DQ237967
DQ237986
Ͳ
DQ238000
Cuvierinacolumnella
Cavoliniidae
Genbank
DQ237965
DQ237984
Ͳ
DQ237998
Pneumodermaatlantica
Pneumodermatidae
Genbank
DQ237970
DQ237989
Ͳ
DQ238003
Spongiobranchaea
australis
Pneumodermatidae
Genbank
DQ237969
DQ237988
Ͳ
DQ238002
Umbraculumumbraculum
Umbraculidae
Genbank
AY165753
AY427457
EF489322
DQ256200
Umbraculumsp.
Umbraculidae
GU213048*
GU213053*
GU213044*
GU213058*
Tylodinaperversa
Tylodinidae
GU213049*
GU213054*
GU213045*
GU213059*
RUNCINACEA
APLYSIOMORPHA
AKEROIDEA
Akerabullata
APLYSIOIDEA
PTEROPODA
THECOSOMATA
GYMNOSOMATA
UMBRACULIDA
MediterraneanSea
France,
MediterraneanSea
129
Tylodinafungina
Tylodinidae
Panama,Caribbean
Sea
GU213050*
GU213055*
GU213046*
GU213060*
ACOCHLIDIACEA
Unelaglandulifera
Microhedylidae
Croatia
AY427517
AY427482
EF489328
GU213061*
Pontohedylemilatchevitchi
Microhedylidae
Genbank
AY427519
AY427484
EF489329
Ͳ
Oxynoeantillarum
Oxynoidae
Genbank
FJ917441
FJ917466
FJ917425
FJ917483
Lobigerviridis
Oxynoidae
Genbank
GU213051*
GU213056*
EU140894
Ͳ
Elysiaviridis
Placobranchidae
Genbank
AY427499
AY427462
EU140863
DQ471211
Placobranchusocellatus
Placobranchidae
Genbank
AY427497
AY427459
DQ480205
DQ471270
Boselliamimetica
Boselliidae
Genbank
AY427498
AY427460
DQ480203
DQ471214
Limapontianigra
Limapontiidae
Genbank
AJ224920
AY427465
Ͳ
Ͳ
Cylindrobullidae
Genbank
EF489347
EF489371
EF489321
Ͳ
Arminalovenii
Arminidae
Genbank
AF249196
Ͳ
AF249243
AF249781
Flabellinaverrucosa
Flabellinidae
Genbank
AF249198
Ͳ
AF249245
AF249790
Eubranchusexiguus
Eubranchidae
Genbank
AJ224787
Ͳ
AF249246
AF249792
Dendronotusdalli
Dendronotidae
Genbank
AY165757
AY427450
AF249252
AF249800
Bathydorisclavigera
Bathydorididae
Genbank
AY165754
AY427444
AF249222
AF249808
Hypselodorisinfucata
Chromodorididae
Genbank
FJ917442
FJ917467
FJ917426
FJ917484
Chromodoriskrohni
Chromodorididae
Genbank
AJ224774
AY427445
AF249239
AF249805
Hoplodorisnodulosa
Discodorididae
Genbank
FJ917443
FJ917469
FJ917428
FJ917486
Austrodoriskerguelenensis
Dorididae
Genbank
AJ224771
Ͳ
EU823269
EU823218
Goniodorisnodosa
Goniodorididae
Genbank
AJ224783
AY014157
AF249226
AJ223264
Acanthodorispilosa
Onchidorididae
Genbank
AJ224770
Ͳ
AJ225177
AJ223254
Limaciaclavigera
Polyceridae
Genbank
AJ224778
Ͳ
EF142952
AJ223268
SACOGLOSSA
OXYNOACEA
PLACOBRANCHACEA
CYLINDROBULLIDA
Cylindrobullabeauii
NUDIPLEURA
NUDIBRANCHIA
DEXIARCHIA
ANTHOBRANCHIA
PLEUROBRANCHOMORPHA
130
Tomthompsonia
antarctica
Pleurobranchinae
Genbank
AY427492
AY427452
EF489330
DQ237992
Pleurobranchusperoni
Pleurobranchinae
Genbank
AY427494
AY427455
EF489331
DQ237993
Berthellinacitrina
Pleurobranchinae
Genbank
FJ917448
FJ917476
FJ917436
FJ917494
Pleurobranchaeameckeli
Pleurobranchaeinae
Genbank
FJ917449
FJ917481
FJ917439
FJ917499
PULMONATA
SIPHONARIOIDEA
Siphonariacapensis
Siphonariidae
Genbank
EF489335
EF489354
EF489301
EF489379
Siphonariaconcinna
Siphonariidae
Genbank
EF489334
EF489353
EF489300
EF489378
Phallomedusasolida
Amphibolidae
Genbank
DQ093440
DQ279991
DQ093484
DQ093528
Amphibolacrenata
Amphibolidae
Genbank
EF489337
EF489356
EF489304
Ͳ
Chilinasp.
Chilinidae
Genbank
EF489338
EF489357
EF489305
EF489382
Lymnaeastagnalis
Lymnaeidae
Genbank
AY427525
AY427490
EF489314
AY227369
Acroloxuslacustris
Acroloxidae
Genbank
AY282592
EF489364
EF489311
AY282581
Latianeritoides
Latiidae
Genbank
EF489339
EF489359
EF489307
EF489384
Bulinustropicus
Bulinidae
Genbank
AY282594
EF489366
EF489313
AY282583
Otinaovata
Otinidae
Genbank
EF489344
EF489363
EF489310
EF489389
Smeagolphillipensis
Smeagolidae
Genbank
FJ917210
FJ917229
FJ917263
FJ917283
Ellobiidae
Genbank
DQ093442
DQ279994
DQ093486
DQ093530
Onchidellafloridana
Onchidiidae
Genbank
AY427521
AY427486
EF489317
EF489392
Onchidiumverrucosum
Onchidiidae
Genbank
AY427522
AY427487
EF489316
EF489391
Arionsilvaticus
Arionidae
Genbank
AY145365
AY145392
EU541969
AF513018
Ariantaarbustorum
Helicidae
Genbank
AY546383
AY014136
AY546343
EF398269
Helixaspersa
Helicidae
Genbank
X91976
AY014128
EU912832
AY546283
Derocerasreticulatum
Limacidae
Genbank
AY145373
FJ917241
FJ917266
FJ917286
AMPHIBOLOIDEA
HYGROPHILA
EUPULMONATA
OTINOIDEA
ELLOBIOIDEA
Ophicardelusornatus
SYSTELLOMMATOPHORA
STYLOMMATOPHORA
131
Reconstruction of character evolution
Character evolution of diet preferences was
reconstructed using a Bayesian approach implemented
in the software package BayesTraits (PC Version 1.0/
Pagel et al., 2004) and based on the phylogenetic tree
derived from Bayesian inference analysis. Reversiblejump Markov chain Monte Carlo (MCMC) methods
were used to derive posterior probabilities of values of
traits at ancestral nodes of phylogenies. MultiState was
selected as model of evolution and the rate deviation
was set to 12. A hyperprior approach was employed
with an exponential prior seeded from an uniform
on the interval 0 to 30. Thus, acceptance rates in the
preferred range of 20 to 40% were achieved. A total
of 5,000,000 iterations were run for each analysis
with the first 50,000 samples discarded as burn-in.
Since posterior probabilities for ancestral states of the
single runs partly varied, we calculated the arithmetic
mean of all samples for reconstruction of the ancestral
condition. Additionally, a Bayes factor test was
conducted to test if there is support for one state over
another as suggested in the BayesTraits manual for
the ancestral diet of Euthyneura. Diet preferences
were taken from the literature and classified as
carnivorous, herbivorous or unselective. Information
on diet and coding for individual taxa and literature
sources are provided in Table 3.
16S-sequences were included to avoid the loss of
phylogenetic signal at lower taxonomic levels.
Results of the relative rate test showed that
evolutionary rates differ among investigated taxa and
genetic markers. The major differences indicated by
the highest z-scores (up to 13.3) were found in the
18S-sequences of the nudibranch taxa Eubranchus
exiguus, Dendronotus dalli, Armina lovenii and
Flabellina verrucosa. Regarding the 28S sequences
the highest z-scores between 5.0 and 7.7 were revealed
for the nudipleuran taxa Dendronotus dalli and
Pleurobranchaea meckeli. 16S and CO1-sequences
generally yielded lower z-scores with maximal values
of slightly more than 3.0 for the 16S-sequences
of Orbitestella sp., Rissoella rissoaformis, the
sacoglossan Oxynoe antillarum, Lobiger viridis and
Elysia viridis as well as Pontohedyle milatchevitchi
and Onchidium verrucosum and for the first codon
position of CO1-sequences of Dendronotus dalli and
Hyalocylis striata as well as the second codon position
of the pteropodan Hyalocylis striata, Pneumoderma
atlantica and Spongiobranchaea australis, and the
pulmonate Helix aspersa, Onchidella floridana
and Deroceras reticulatum. In the concatenated
alignment the influence of the 18S sequences is strong
yielding z-scores of above 10.0 for the nudibranch
taxa Eubranchus exiguus, Dendronotus dalli, Armina
lovenii and Flabellina verrucosa.
RESULTS
Phylogenetic analyses
Statistical tests
The Incongruence Length Difference test (ILD)
yielded a p-value of 0.01 implying that concatenation
of the four single gene fragments significantly
improves the phylogenetic signal.
Bayesian inference analysis yielded a well
resolved tree topology with robust statistical support
of terminal branches as well as deeper nodes. The
phylogram of the Bayesian analysis with posterior
probabilities given at the nodes is shown in Fig. 1.
Evaluation of substitution saturation revealed
little saturation in the 16S-alignment and substantial
saturation in the 3rd codon position of CO1, although
only 22 bp of this position were left after filtering
with Aliscore. Thus the 3rd codon position of CO1
was excluded from further analyses, while the
The Euthyneura comprising Opisthobranchia
and Pulmonata are retrieved as monophyletic in
our analyses. In contrast to this, monophyly of the
Opisthobranchia is clearly rejected by our analyses
mainly due to the position of the Sacoglossa and the
Acochlidiacea clustering well supported within the
132
(also polyphyletic) pulmonate taxa included in the
analyses. We additionally conducted an Approximately
Unbiased (AU) test to reevaluate this result. This test
yielded a p-value of 0.997 for the unconstrained
topology implying polyphyly of the Opisthobranchia,
while a p-value of 0.003 was revealed for enforced
monophyly of the Opisthobranchia. The latter value is
below the significance value of 0.050 thus monophyly
of the Opisthobranchia is definitely rejected based on
our dataset.
apart from the remaining Cephalaspidea. The
latter receive maximum statistical support with the
Diaphanidae found in a basal position and a further
supported division into two main clades. The first
clade comprises Bulla striata and the Retusidae,
while the second is composed of the two superfamilies
Haminoeoidea and Philinoidea. The latter clade is
found to be paraphyletic due to the position of the
Retusidae who are traditionally assigned to this
superfamily.
The “lower heterobranch” outgroup taxa cluster
well supported basal to all other taxa included in
our analyses. The Acteonoidea are revealed as sister
group of the Rissoelloidea, together representing
the sister group of Euthyneura. With regards to
Euthyneura three main clades are recovered which are
supported by maximal posterior probability values.
The Aplysiomorpha and Pteropoda form a well
supported subclade within this main clade being sister
taxon to the Runcinacea. However, statistical support
for this sister group relationship is non-existent and
therefore this grouping should be considered with
care. Akera bullata is found as the most basal offshoot
rendering the Aplysiomorpha paraphyletic since the
remaining Aplysiomorpha included in our study form
the sister group of the Pteropoda. The Pteropoda
themselves are divided into the two main subclades
Gymnosomata and Thecosomata.
The first offshoot of the three euthyneuran clades
is the Nudipleura. Monophyly of the Nudipleura as well
as of the two main subclades Pleurobranchomorpha
and Nudibranchia is supported by maximum
statistical support values. The Nudibranchia are
furthermore divided into monophyletic Dexiarchia
and Anthobranchia.
The two other clades form sister groups. One
clade comprises the opisthobranch subclades
Umbraculida, Cephalaspidea, Aplysiomorpha and
Pteropoda (called Euopisthobranchia by Jörger et
al., 2010), while the other clade is composed of the
pulmonate taxa and the opisthobranch subclades
Sacoglossa and Acochlidiacea (termed Panpulmonata
by Jörger et al., 2010). The interrelationships of the
opisthobranch subclades in the Euopisthobranchia are
poorly resolved.
Monophyly of the Umbraculida and its two
families Umbraculidae and Tylodinidae is strongly
supported while their position basal to all other
taxa in this clade lacks statistical support. The
Cephalaspidea are rendered paraphyletic due to the
unresolved position of the Runcinacea clustering
The third main clade revealed in this study
comprises pulmonate taxa and the opisthobranch
Sacoglossa and Acochlidiacea (Panpulmonata).
Monophyly of the main subclades (Siphonarioidea,
Hygrophila, Amphiboloidea and Eupulmonata)
is supported, but the Pulmonata are rendered
paraphyletic due to the inclusion of Sacoglossa
and Acochlidiacea. The whole clade is divided
into three main subclades without statistically
supported interrelationships. These subclades are the
Siphonarioidea found monophyletic as the most basal
offshoot, the Sacoglossa and a subclade comprising
Hygrophila, Amphiboloidea, Acochlidiacea and
Eupulmonata. The Sacoglossa are found to be
monophyletic and display a well supported division
into two main monophyletic subclades; on the one
hand the Plakobranchacea and on the other hand the
Oxynoacea clustering with the cylindrobullid taxon.
The monophyletic Hygrophila are found as the most
basal offshoot of the third subclade, without statistical
133
Table 2:
Information on sequence alignments of the single markers and models of sequence evolution for Baysian analyses (pinv/I =
proportion of invariable sites; α/G = gamma distribution shape parameter; GTR = General Time Reversible).
Generegion
18SrDNA
Numberof
taxa
Lengthofalignment(afterremoval
ofambiguouspositions)
Excludednucleotidepositions
(byAliscore)
43Ͳ48,113Ͳ117,160Ͳ163,179Ͳ192,230Ͳ
86
1783
320,366Ͳ370,718Ͳ720,774Ͳ829,841Ͳ
pinv=0.3796
864,871Ͳ908,929Ͳ1250,1264Ͳ1270,
ɲ=0.4720
1367Ͳ1375,1705Ͳ1723,1993Ͳ2213,
2221Ͳ2229,2350Ͳ2356,2372Ͳ2374,
2562Ͳ2590,2598Ͳ2602,2663
28SrDNA
96Ͳ100,141Ͳ150,216Ͳ218,460Ͳ480,487Ͳ
GTR+I+G
79
954
502,511Ͳ567,574Ͳ586,640Ͳ647,664Ͳ
pinv=0.2752
672,686Ͳ750,764Ͳ809,836Ͳ845,856Ͳ
ɲ=0.6188
GTR+I+G
865,875Ͳ877,904Ͳ907,937Ͳ959,966Ͳ
988,1150Ͳ1413,1540Ͳ1557
72
269
3Ͳ22,30Ͳ35,47Ͳ64,142Ͳ152,155Ͳ159,
GTR+I+G
170Ͳ186,196Ͳ199,215Ͳ226,258Ͳ415,
pinv=0.2750
434Ͳ552,587Ͳ612,644Ͳ652,662Ͳ675,
ɲ=0.5667
690Ͳ698
80
197
80
203
16SrDNA
st
CO1(1 position)
nd
CO1(2 position)
support, so that the interrelationships of Hygrophila,
Amphiboloidea and a clade of Acochlidiacea and
Eupulmonata cannot be finally resolved. However,
weak statistical support is given for a sister group
relationship of Acochlidiacea and Eupulmonata.
Within the latter grouping good support is received for
a sister group relationship of Otinoidea/Ellobioidea
with Systellommatophora together representing the
sister group of the Stylommatophora.
The split network analysis (Fig. 2) confirms
conflict in the dataset. Additionally, it becomes
obvious that evolutionary rates and thus distances
between taxa differ since lengths of edges vary
between different clades.
134
Modelofsequence
evolution
22Ͳ24,92Ͳ94
GTR+I+G
pinv=0.2731
ɲ=0.6195
Ͳ
GTR+G
pinv= 0.3048
ɲ=0.7436
Most opisthobranch and pulmonate subclades
receive split support in our network analysis; however
no split support could be detected for relationships
among the different subclades.
In the outgroup and “lower heterobranch” taxa
good split support is revealed for the Acteonoidea
with some conflict regarding Acteon tornatilis which
shares split support with the Acteonoidea as well as
with some nudibranch taxa. The remaining “lower
heterobranch” taxa cluster apart from the Acteonoidea
without split support for these taxa.
Considerable split support is found for the
Nudipleura which exhibit very long parallel edges
indicating high evolutionary rates compared to
other taxa included in this analysis. Extensively
long edges are present for the nudibranch subclade
Dexiarchia, shorter ones lead to the Anthobranchia
and Pleurobranchomorpha.
Furthermore, considerable split support is detected for each of the following taxa: Umbraculida,
Aplysiomorpha and Cephalaspidea (without the taxon
Runcinacea which itself receives good split support).
No split support could be detected for Sacoglossa
in our analysis; however the main subclades
Plakobranchacea and Oxynoacea plus Cylindrobulla
beauii receive considerable split support.
Additionally, no split support is found for the Pteropoda
as their main subclades Thecosomata and Gymnosomata
are separated by the acochlid Pontohedyle milatchevitchi
sharing split support with the Gymnosomata which
themselves also receive good split support.
The most surprising results are revealed for
the Acochlidiacea which are not only lacking split
support but even cluster far apart in our network
analysis. As already mentioned P. milatchevitchi
shares split support with the Gymnosomata while
Unela glandulifera shares split support with both
Eupulmonata and Hygrophila.
Regarding the pulmonate taxa good split support
is found for the Stylommatophora. Conflicting
signals are found considering the interrelationships of
Eupulmonata, since on the one hand split support is
given for a clade composed of Otinoidea/Ellobioidea
and Systellommatophora and on the other hand
for Otinoidea/Ellobioidea and Stylommatophora.
Generally, it becomes obvious that all pulmonate
subclades are difficult to separate in this network
analyses probably because their evolutionary rates are
so much lower than those of the other clades included.
Thus, Amphiboloidea is the only other pulmonate
subclade with detectable split support although the
other taxa cluster in the expected clades as well.
Reconstruction of character evolution
Our molecular phylogenetic analyses unambiguously revealed polyphyly of Opisthobranchia, thus
reconstruction of ancestral diet preferences was performed for monophyletic Euthyneura (comprising
Opisthobranchia and Pulmonata) as well as its sister
group consisting of Acteonoidea and Rissoelloidea.
Furthermore, we traced dietary evolution for all main
lineages detected in our molecular systematic studies
and all relevant opisthobranch and pulmonate clades.
The results are given as pie charts displaying different
fractions (calculated as posterior probabilities) of the
reconstructed dietary types and mapped onto the
phylogenetic tree in Fig. 3. Details about the posterior
probabilities for all investigated clades are provided
in Table 4.
The reconstruction of dietary evolution of the
Euthyneura strongly suggests that the last common
ancestor was herbivorous. The posterior probability
value for the herbivorous state is 0.85 compared
with 0.14 for a carnivorous state and 0.01 for an
unselective diet. The Bayes Factor test yielded a
value of ~4.0 preferring the herbivorous state over the
carnivorous one and of ~8 preferring herbivory over
the unselective state. Thus, there is support for an
herbivorous state at this node.
The last common ancestor of Euthyneura along
with the Acteonoidea/Rissoelloidea clade was
possibly also an herbivore (posterior probability:
0.77, carnivore: 0.21, unselective: 0.02). In contrast
to this, ancestral Nudipleura representing the first
offshoot of the Euthyneura most likely switched to
carnivory, while the last common ancestor of all other
Euthyneura included in this investigation was probably
a herbivore (posterior probability: 0.89, carnivore:
0.10, unselective: 0.01). The same holds true for the
two main subclades of the latter clade composed
of the opisthobranch Umbraculida, Cephalaspidea,
Aplysiomorpha and Pteropoda (Euopisthobranchia)
on the one hand and the pulmonate taxa along
with the opisthobranch Sacoglossa and Acochlidiacea
135
(Panpulmonata) on the other hand. Both subclades
received high posterior probabilities for the
herbivorous state (0.79 and 0.98, respectively).
Regarding the opisthobranch clades ancestral
diet preferences differ. The last common ancestors
of Nudipleura and Umbraculida probably were
carnivorous, while the common ancestors of
Cephalaspidea, Aplysiomorpha and Sacoglossa most
probably were herbivores. The last common ancestor
of the Pteropoda probably also was a carnivore, but
herbivorous as well as unselective diet also received
unexpectedly high posterior probabilities (carnivore:
0.62, herbivore: 0.12, unselective: 0.26).
In summary, the results of the present study
strongly support herbivorous diet as ancestral for
all Euthyneura. Carnivorous diet evolved at least
five times independently according to our results (in
Nudipleura, Umbraculida, Pteropoda (Gymnosomata)
and twice in the Cephalaspidea). Furthermore, a
generalization to unselective diet occurred randomly
across most clades.
DISCUSSION
Phylogeny of the Euthyneura
The results of the present study confirm
monophyly of the Euthyneura while monophyly of
the Opisthobranchia is strongly rejected. Hitherto,
monophyly of Euthyneura was mainly based on
morphological analyses (Ponder and Lindberg, 1997;
Dayrat and Tillier, 2002; Wägele and KlussmannKolb, 2005) since members of this clade reveal
common features of the nervous (Haszprunar, 1985)
and reproductive system (Gosliner, 1981). Molecular
systematic studies seldom revealed monophyly
(Thollesson, 1999; Wade and Mordan, 2000; Knudsen
et al., 2006); paraphyly was revealed more often,
however mostly due to the position of clades with
uncertain systematic affinity like the Pyramidellidae
(Grande et al., 2004b; Klussmann-Kolb et al., 2008;
Dinapoli and Klussmann-Kolb, 2010; Jörger et
136
al., 2010) or the Acteonoidea (Dayrat et al., 2001;
Klussmann-Kolb et al., 2008). Jörger et al. (2010)
claim inclusion of (formerly lower heterobranch) taxa
Pyramidellidae and Glacidorboidea into Euthyneura
thus regaining monophyly of the clade.
Monophyly of Opisthobranchia was challenged
before since there are very few common apomorphic
features for this clade (Salvini-Plawen and
Steiner, 1996) and phylogenetic analyses based on
morphological or molecular data repeatedly yielded
paraphyly or even polyphyly of this clade (Thollesson,
1999; Dayrat et al., 2001; Dayrat and Tillier, 2002;
Grande et al., 2004a, b; Wägele and Klussmann-Kolb,
2005; Klussmann-Kolb et al., 2008; Dinapoli and
Klussmann-Kolb, 2010; Jörger et al., 2010). This result
is supported by our analyses comprising the most
extensive taxon sampling of all mentioned studies.
Monophyly of Opisthobranchia is rejected in all our
analyses and based on several levels of evidence
(statistical tests, phylogenetic reconstruction, split
network analysis).
Monophyly of Pulmonata is generally accepted
based on morphological data (Tillier, 1984;
Haszprunar, 1985; Nordsieck, 1992; Dayrat and
Tillier, 2002). On the contrary, molecular data were
not able to recover monophyly of this clade (Tillier
et al., 1996; Grande et al., 2004b, 2008; Knudsen
et al., 2006; Klussmann-Kolb et al., 2008; Dinapoli
and Klussmann-Kolb, 2010; Jörger et al., 2010). The
results of the present study also support paraphyly of
the Pulmonata. This is mainly due to the position of
the supposedly opisthobranch taxon Acochlidiacea.
Jörger et al. (2010) have proposed Acochlidiacea to be
closely related to Eupulmonata. This is confirmed by
our results. The position of the Sacoglossa which also
cluster in between the pulmonate taxa is unresolved.
They might represent the first offshoot of the whole
clade rendering Pulmonata (including Acochlidiacea)
monophyletic. Inclusion of both Sacoglossa and
Acochlidiacea into Pulmonata would support the
Panpulmonata-concept proposed by Jörger et al.
(2010).
The phylogenetic affinities of the Acteonoidea
have been a matter of debate for a long time. They were
either regarded as opisthobranchs mostly inhabiting a
basal position (Gosliner, 1981, 1994; Ponder and
Lindberg, 1997; Burn and Thompson, 1998; Dayrat
and Tillier, 2002; Grande et al., 2004a, b; Vonnemann
et al., 2005; Klussmann-Kolb et al., 2008) or excluded
into the “lower Heterobranchia” (Mikkelsen, 1996,
2002; Thollesson, 1999; Dayrat et al., 2001; Bouchet
and Rocroi, 2005; Wägele and Klussmann-Kolb,
2005; Dinapoli and Klussmann-Kolb, 2010; Jörger et
al., 2010). The present study recovers the Acteonoidea
as sister group of the Rissoelloidea who are assigned
to the “lower Heterobranchia” (Bouchet and Rocroi,
2005). Together both clades represent the sister
group of the Euthyneura underlining the “lower
heterobranch” position of Acteonoidea outside but
close to the Opisthobranchia.
The first offshoot of the Euthyneura is represented
by the opisthobranch clade Nudipleura. The Nudipleura
were established in 2000 by Wägele and Willan and
are composed of the sister taxa Nudibranchia and
Pleurobranchomorpha. Monophyly of the Nudipleura
as well as of Nudibranchia and Pleurobranchomorpha
is supported by maximum statistical support values
and considerable split support and is in accordance
with former studies (Vonnemann et al., 2005; Wägele
and Klussmann-Kolb, 2005; Klussmann-Kolb et al.,
2008; Dinapoli and Klussmann-Kolb, 2010; Göbbeler
and Klussmann-Kolb, 2010; Jörger et al. 2010).
However, the basal position of this morphologically
derived clade is somewhat surprising although it has
been revealed in most molecular systematic studies.
Nudipleura either cluster as sister group to the possibly
“lower heterobranch” clade Acteonoidea (Grande et
al., 2004a, b; Vonnemann et al., 2005; KlussmannKolb et al., 2008) or represent the single first offshoot
of Euthyneura like in the present study (Dinapoli
and Klussmann-Kolb, 2010; Jörger et al., 2010).
These results suggest that the last common ancestor
of the Nudipleura evolved early as sister taxon to
the last common ancestor of all other Euthyneura.
This early off split might also be the reason for
the high evolutionary rates present in Nudipleura
compared to all other taxa in this analysis resulting
in long branches in the phylogenetic tree and network
analyses. If the Nudipleura split off early there
was plenty of time for accumulation of nucleotide
changes. Unfortunately, this assumption cannot be
underlined by the fossil record since the Nudibranchia
lack any fossils because of their missing shells and
the oldest known pleurobranchomorph fossil is only
dated back to about 26 Million years ago (Valdes
and Lozouet, 2000). This suggests that this clade
is rather young, but, due to their small and delicate
shells the fossil record of the Pleurobranchomorpha is
likely incomplete (Valdes, 2004). Otherwise, the high
evolutionary rates might hamper proper phylogenetic
reconstruction and contribute to a basal placement of
a derived clade. However, according to the results of
the present study it seems reasonable to suggest that
the last common ancestor of Nudipleura separated
early in evolution of euthyneuran gastropods and
that Nudipleura represent a single offshoot without a
specific sister taxon.
A clade composed of Umbraculida, Cephalaspidea,
Aplysiomorpha and Pteropoda is the only monophyletic
clade uniting several opisthobranch taxa; all other
clades (Nudipleura, Sacoglossa and Acochlidiacea)
cluster separately. The clade of Umbraculida,
Cephalaspidea, Aplysiomorpha and Pteropoda
has also been found in other molecular systematic
analyses (Klussmann-Kolb et al., 2008; Dinapoli and
Klussmann-Kolb, 2010; Göbbeler and KlussmannKolb, 2010; Jörger et al., 2010) while it could not
be revealed in morphological analyses (Wägele and
Klussmann-Kolb, 2005) since common characters
are missing (Klussmann-Kolb and Dinapoli, 2006).
However, Jörger et al. (2010) proposed to erect the
taxon Euopisthobranchia for these opisthobranchs and
proposed the presence of a gizzard as the unifying
synapomorphy.
The Cephalaspidea are rendered paraphyletic in
our analyses due to the exclusion of the Runcinacea
137
Table 3: Information on dietary of investigated species coded as carnivorous, herbivorous or unspecific.
Literature sources for dietary information provided. - = unknown
Carnivorous
Herbivorous
Unselective
Reference
algae
Lubchenco,1978
CAENOGASTROPODA
Littorinalittorea
LOWERHETEROBRANCHIA
Orbitestellasp.
unicellularplants,
detritus
PonderanddeKeyzer,
1998
Cimasp.
Ͳ
Rissoellarissoaformis
Bacillariophyceae,
algalfilaments,
detritus
Fretter,1948
Acteontornatilis
Polychaeta
Yonow,1989
Pupanitidula
Polychaeta
Rudman,1972a
Hydatinaphysis
Polychaeta
Rudman,1972b
Micromeloundata
Polychaeta
BurnandThompson,
1998
Bullinalineata
Polychaeta
Taylor,1986
ACTEONOIDEA
OPISTHOBRANCHIA
CEPHALASPIDEA
BULLOIDEA
Bullastriata
algae
Malaquiasetal.,2009a
Diaphanasp.
Ͳ
Toledoniaglobosa
Ͳ
Haminoeahydatis
algae
Malaquiasetal.,2009a
Atyscylindricus
algae
Helbling,1779
Smaragdinellasp.
algae
Rudman,1972c
Foraminifera,
Polychaeta,Bivalvia,
Gastropoda,
Crustacea,
Echinodermata
Hurst,1965
DIAPHANOIDEA
HAMINOEOIDEA
PHILINOIDEA
Scaphanderlignarius
138
Philineaperta
Bivalvia
Hansen,1991
Odontoglajasp.
Polychaeta,Bivalvia
Rudman,1978
Philinopsispilsbryi
Opisthobranchia
Rudman,1972d
Sagaminopteron
psychedelicum
Porifera
Becerroetal.,2006
Philinoglossapraelongata
Ͳ
Retusasp.
Foraminifera,small
Mollusca
BurnandThompson,
1998
Pyrunculussp.
Foraminifera,small
Mollusca
BurnandThompson,
1998
Runcinaafricana
algae
Rudman,1971
Ilbiailbi
algae
Rudman,1971
algae
Haywardetal.,1990
Aplysiacalifornica
algae
Carefoot,1981
Dolabriferadolabrifera
algae
Willan,1998a
Bursatellaleachii
algae
Paige,1988
Dolabellaauricularia
algae
Penningsetal.,1993
Stylocheiluslongicauda
algae,Cyanobacteria
Nagleetal.,1998
Petaliferapetalifera
algae
Willan,1998a
Cavoliniauncinnata
Bacillariophyceae,
Dinoflagellata,
Foraminifera,
Radiolaria,
zooplankton,
phytoplankton
Newman,1998
Hyalocylisstriata
Bacillariophyceae,
Dinoflagellata,
Foraminifera,
Radiolaria,
zooplankton,
phytoplankton
Boltovskoy,1975
Cliopyramidata
Bacillariophyceae,
Dinoflagellata,
Foraminifera,
Radiolaria,
Newman,1998
RUNCINACEA
APLYSIOMORPHA
AKEROIDEA
Akerabullata
APLYSIOIDEA
PTEROPODA
THECOSOMATA
139
zooplankton,
phytoplankton
Bacillariophyceae,
Dinoflagellata,
Foraminifera,
Radiolaria,
zooplankton,
phytoplankton
Newman,1998
Pneumodermaatlantica
zooplankton
PafortͲvanIersel,1985
Spongiobranchaeaaustralis
carnivorous
Richter,1977
Umbraculumumbraculum
Porifera
Willan,1984
Umbraculumsp.
Porifera
Willan,1984
Tylodinaperversa
Porifera
Cyanobacteria
Becerroetal.,2003
(nutritionalvalue
unclear,codedas
“unknown”)
Tylodinafungina
Porifera
Gabb,1865
Unelaglandulifera
microorganisms
Burn,1998a
Pontohedylemilatchevitchi
microorganisms
Burn,1998a
Oxynoeantillarum
algae
Morch,1863
Lobigerviridis
algae
Morch,1863
Elysiaviridis
algae
Thompson,1976
Placobranchusocellatus
algae
Burn,1998b
Boselliamimetica
algae
Marcus,1978
Limapontianigra
algae
Thompson,1976
algae
Burn,1998b
Cuvierinacolumnella
GYMNOSOMATA
UMBRACULIDA
ACOCHLIDIACEA
SACOGLOSSA
OXYNOACEA
PLACOBRANCHACEA
CYLINDROBULLIDA
Cylindrobullabeauii
NUDIPLEURA
NUDIBRANCHIA
DEXIARCHIA
140
Arminalovenii
Cnidaria
Thompson,1988
Flabellinaverrucosa
Cnidaria
ThompsonandBrown,
1984
Eubranchusexiguus
Cnidaria
Thompson,1988
Dendronotusdalli
Cnidaria
Bergh,1879
Bathydorisclavigera
Wägele,1989
Hypselodorisinfucata
Porifera
omnivorous,e.g.
Foraminifera,
Porifera,Cnidaria,
Echinodermata,
Polychata,Mollusca
Chromodoriskrohni
Porifera
RudmanandBergquist,
2007
Hoplodorisnodulosa
Ͳ
Austrodoriskerguelenensis
Porifera
Wägele,1989
Goniodorisnodosa
Bryozoa,Ascidiacea
Thompson,1988
Acanthodorispilosa
Bryozoa
Müller,1788
Limaciaclavigera
Bryozoa
Müller,1776
Tomthompsoniaantarctica
(nonͲselective)
benthicdeposit,e.g.
Bacillariophyceae,
Radiolaria,Porifera,
Bryozoans
Hainetal.,1993
Pleurobranchusperoni
Ascidiacea
Cuvier,1804
Berthellinacitrina
Porifera
Willan,1984
Pleurobranchaeameckeli
Cnidaria,Porifera,
Polychata,Mollusca
CattaneoͲViettietal.,
1993
ANTHOBRANCHIA
Fontana,1993
PLEUROBRANCHOMORPHA
PULMONATA
SIPHONARIOIDEA
Siphonariacapensis
algae
Maneveldt,2006
Siphonariaconcinna
algae
Gray,1997
Phallomedusasolida
detritus,
Bacillariophyceae
Schacko,1878
Amphibolacrenata
detritus
Stanisic,1998a
microalgae
Brace,1983
AMPHIBOLOIDEA
HYGROPHILA
Chilinasp.
141
Lymnaeastagnalis
detritus,carrion
Sterry,1997
Acroloxuslacustris
Bacillariophyceae,
algae,rottedplants
Dillon,2000
Latianeritoides
Bacillariophyceae,
detritus
MeyerͲRochowand
Moore,1988
Bulinustropicus
detritus,greenalgae,
Bacillariophyceae
Madsen,1992
Otinaovata
Ͳ
Smeagolphillipensis
Ͳ
algae
Rossetal.,2009
EUPULMONATA
OTINOIDEA
ELLOBIOIDEA
Ophicardelusornatus
SYSTELLOMMATOPHORA
Onchidellafloridana
algae
Stanisic,1998b
Onchidiumverrucosum
algae
Arionsilvaticus
deadwood,detritus
KerneyandCameron,
1979
Ariantaarbustorum
plants
Hägele,2001
Helixaspersa
plants
Iglesias,1999
Derocerasreticulatum
plants
Stanisic,1998b
STYLOMMATOPHORA
SchleyandBees,2003
which are commonly assigned to this taxon (Burn and
Thompson, 1998; Bouchet and Rocroi, 2005) and have
been revealed as sister group to all Cephalaspidea
(Grande et al., 2004a, b; Vonnemann et al., 2005).
Malaquias et al. (2009b) performed extensive analyses
on cephalaspidean phylogeny recovering exclusion of
Runcinacea from the Cephalaspidea in all analytical
attempts. Thus, he proposed (p. 36) that “Runcinacea
should be reinstated as a distinct taxonomic category
of equivalent rank to Cephalaspidea s.s.”; a postulation
supported by the present study. Additionally, the
current study is the first to include more than one
genus of Runcinacea. Ilbia ilbi as member of the
Ilbiidae which were classified as incertae sedis by
142
Malaquias et al. (2009b) is the sister taxon to Runcina
africana of the Runcinidae rendering the Runcinacea
monophyletic. Another controversial cephalaspidean
family is the Diaphanidae which has been excluded
from the Cephalaspidea and assigned to different
clades several times (e.g. Haszprunar, 1985; SalviniPlawen and Steiner, 1996; Jensen, 1996a). According
to our results the Diaphanidae are definitely part of
the Cephalaspidea since they share split support and
receive maximum statistical support values in tree
reconstruction. They are recovered basal to all other
cephalaspidean taxa included in the present study
which is in congruence with the results of Malaquias
et al. (2009b).
The only statistically supported grouping in this
clade of Euopisthobranchia unites Aplysiomorpha
and Pteropoda. In this clade the aplysiomorph
Akera bullata is found as the most basal offshoot
which is consistent with former studies (Medina
and Walsh, 2000; Vonnemann et al., 2005; Wägele
and Klussmann-Kolb, 2005) while the remaining
Aplysiomorpha form the sister group to the Pteropoda
rendering the Aplysiomorpha paraphyletic. In contrast
to this, the split network analysis reveals good support
for monophyletic Aplysiomorpha and monophyly of
this clade has not been doubted in most phylogenetic
analyses before (Thollesson, 1999; Medina and Walsh,
2000; Dayrat and Tillier, 2002; Grande et al., 2004a,
b; Vonnemann et al., 2005; Wägele and KlussmannKolb, 2005; Klussmann-Kolb et al., 2008). Hence, this
result needs to be considered with caution and needs
further investigation involving different markers and
possibly more taxa.
The common ancestry of Aplysiomorpha and
Pteropoda as found in the present study has already
been revealed in a molecular systematic study of
Dayrat et al. (2001) and was also recovered in
an extensive study on pteropodan phylogeny
(Klussmann-Kolb and Dinapoli, 2006). Furthermore,
monophyly of Pteropoda comprising Gymnosomata
and Thecosomata as sister taxa has been revealed
in molecular systematic studies before (KlussmannKolb and Dinapoli, 2006; Klussmann-Kolb et al.,
2008, Jörger et al., 2010) and is confirmed in the
current study. Morphological studies and traditional
classifications by Thiele (1931), Hoffmann (1939) and
Odhner (1939) also support monophyly of Pteropoda.
The third main clade revealed in our analyses
is composed of the Pulmonata along with the
opisthobranch clades Sacoglossa, Cylindrobullida
and Acochlidiacea. Jörger et al. (2010) proposed the
new clade Panpulmonata to unite these taxa. This
clade is further divided into three main subclades:
Siphonarioidea, Sacoglossa and a statistically
supported clade of Hygrophila, Amphiboloidea,
Acochlidiacea and Eupulmonata. Siphonarioidea
represent the first offshoot in this clade while
Sacoglossa form the sister group to the third subclade.
However, these interrelationships did not receive
statistical support. Similar though more or less
unresolved interrelationships were also revealed in
a study by Dinapoli and Klussmann-Kolb (2010)
while Klussmann-Kolb et al. (2008) and Jörger et
al. (2010) recovered a sister group relationship of
Siphonarioidea and Sacoglossa together representing
the sister group to the third subclade. Phylogenetic
affinities of the Sacoglossa have also been a
matter of debate from morphological perspectives.
Sacoglossa could hardly be linked to any other extant
opisthobranch taxon (besides Cylindrobullida), since
any apparent synapomorphy might be explained as
parallel evolution (Jensen, 1996b).
According to the present study the Sacoglossa
incorporate Cylindrobulla beauii. This taxon was
supposed to be part of a separate monogeneric
“group” called Cylindrobullida before (Bouchet and
Rocroi, 2005) which was regarded as the sister group
of the Sacoglossa (Jensen, 1996b). C. beauii clusters
along with the oxynoacean taxa included in this
study receiving both maximum statistical support in
tree reconstruction and considerable split support in
network analysis. The latter has also been found in a
molecular systematic study on Sacoglossan phylogeny
(Händeler and Wägele, 2006) as well as in the
most recent broad euthyneuran study performed by
Jörger et al. (2010). Furthermore, Cylindrobullida was
supposed to belong to the Oxynoacea in morphologybased analyses (Mikkelsen, 1996, 2002). Thus, we
suggest that the Cylindrobullida do not form a separate
clade but possibly represent a subclade of sacoglossan
Oxynoacea. Furthermore, the divison of Sacoglossa in
two main subclades (Oxynoacea and Plakobranchacea)
recovered in the present study is in accordance with
former classifications (Jensen, 1996b; Bouchet and
Rocroi, 2005; Händeler and Wägele, 2006; Händeler
et al., 2009) and receives high statistical support
in tree reconstruction. However, split support for
Sacoglossa is missing and only present for the two
subclades.
143
Table 4:
Detailed results of the BayesTraits analyses. Arithmetic means of posterior probabilities (rounded to two decimal places) of
the different diet preferences of last common ancestor of the diverse clades are provided. The highest values for each clade are
highlighted in bold.
Clade
Acteonoidea/Euthyneura
Herbivorous
Unselective
0.21
0.77
0.02
Euthyneura
0.14
0.85
0.01
EuthyneurawithoutNudipleura
0.10
0.89
0.01
Umbraculida/Cephalaspidea/Aplysiomorpha/Pteropoda
(Euopisthobranchia)
0.21
0.79
0
0
0.98
0.02
0.82
0.10
0.08
Pulmonata/Sacoglossa/Acochlidiacea(Panpulmonata)
Acteonoidea/Rissoelloidea
Acteonoidea
1
0
0
Nudipleura
0.85
0.08
0.07
Umbraculida
0.99
0.01
0
CephalaspideawithoutRuncinacea
0.24
0.73
0.03
Cephalaspidea/Aplysiomorpha/Pteropoda
0.09
0.90
0.01
Runcinacea/Aplysiomorpha/Pteropoda
0
0.99
0.01
Aplysiomorpha/Pteropoda
0
1
0
Aplysioidea
0
1
0
Aplysioidea/Pteropoda
0.01
0.98
0.01
Pteropoda
0.62
0.12
0.26
Sacoglossa
0
0.99
0.01
Sacoglossa/Hygrophila/Amphiboloidea/Acochlidiacea/Eupulmonata
0
0.89
0.11
Hygrophila
0
0.74
0.26
Hygrophila/Amphiboloidea/Acochlidiacea/Eupulmonata
0
0.67
0.33
Amphiboloidea/Acochlidiacea/Eupulmonata
Acochlidiacea/Eupulmonata
Eupulmonata
The subclade composed of Hygrophila,
Amphiboloidea, Acochlidiacea and Eupulmonata
receives good statistical support. However,
interrelationships of these groups remain partly
unresolved. Monophyly of the single subclades is
strongly supported in phylogenetic reconstruction.
Furthermore, a sister group relationship of the
Acochlidiacea and the Eupulmonata receives a
posterior probabilities value of 0.94 which is close
to the significance level of 0.95. This relationship
supports the findings by Jörger et al. (2010) and an
144
Carnivorous
0
0.68
0.32
0.01
0.82
0.17
0
0.99
0.01
affinity to pulmonate taxa has repeatedly been
proposed before (Vonnemann et al., 2005; KlussmannKolb et al., 2008). In contrast to this, morphological
investigations reveal Acochlidiacea as sister group
to part of (polyphyletic) Cephalaspidea within other
opisthobranch clades (Wägele and KlussmannKolb, 2005) or regard them as sister group of the
Sacoglossa (Gosliner and Ghiselin, 1984). However,
within these different clades Acochlidiacea group
with other mesopsammic taxa suggesting convergent
adaptions to this special habitat might mask the
phylogenetic signal (Schrödl and Neusser, 2010).
Monophyly of Acochlidiacea is strongly supported
in our tree reconstruction analysis and has also
been revealed in former studies (Vonnemann et
al., 2005; Wägele and Klussmann-Kolb, 2005;
Klussmann-Kolb et al., 2008). Surprisingly both
included taxa of Acochlidiacea cluster far apart in
our network analyses. Unela glandulifera clusters
among eupulmonate taxa resembling placement
of the whole clade in tree reconstruction, while
Pontohedyle milatchevitchi shares spilt support with
Gymnosomata. Nevertheless, Acochlidiacea might
be monophyletic and share split support which is
not revealed in the graphical output of the split
network analyses showing a two dimensional picture
of relationships of diverse taxa. Furthermore, the
Acochlidiacea have never been associated with the
Pteropoda, so that we would regard the latter result
as erroneous and still consider the Acochlidiacea (as
well as the Pteropoda) as monophyletic.
The Eupulmonata consist of Stylommatophora,
Systellommatophora, Ellobioidea and Otinoidea
(Bouchet and Rocroi, 2005). Several molecular
systematic studies support their monophyly (Tillier et
al., 1996; Wade and Mordan, 2000; Klussmann-Kolb
et al., 2008; Dinapoli and Klussmann-Kolb, 2010)
including the present one. Moreover, monophyly
of Stylommatophora is revealed in the present
investigation which is in accordance with several
other studies (e.g. Tillier et al., 1996; Wade and
Mordan, 2000; Dayrat and Tillier, 2002; Grande et al.,
2004b, 2008; Klussmann-Kolb et al., 2008; Dinapoli
and Klussmann-Kolb, 2010). The Stylommatophora
form the sister-group of a clade composed of
Systellommatophora, Ellobioidea and Otinoidea,
which is congruent with the results of Dinapoli and
Klussmann-Kolb (in 2010) as well.
Evolution of diet
Ancestral diet preferences of Opisthobranchia
have been a matter of debate because the evolution of
special nutrition strategies as well as the specialization
on particular food items were discerned to be crucial
features for the evolution of this clade (Thompson,
1976; Rudman and Willan, 1998; Mikkelsen, 2002;
Wägele, 2004). Major evolutionary radiations of
opisthobranchs are connected to habitat and diet
(Rudman and Willan, 1998; Wägele, 2004). The
occupation of diverse feeding niches enabled by
development of particular morphological structures
for dietary specialization is even considered as
the “driving force” of opisthobranch evolution
(Thompson, 1976; Mikkelsen, 2002).
Nevertheless up to now, assessment of their
trophic relationships was mainly based on scattered
data (Malaquias et al., 2009a). We conducted a
thorough literature search to compile information on
dietary sources of a great variety of species in order to
reconstruct the ancestral diet preferences of this clade.
Opisthobranch gastropods reveal highly specialized
feeding habits which may be classified into different
categories regarding their size, feeding mode or
type of food. This study focuses on reconstructing
dietary preferences based on a division in herbivorous
versus carnivorous sources, additionally coding for
unselective food items. The reconstruction is based
on a robust molecular phylogenetic hypothesis for the
respective taxa.
Our molecular systematic analyses unambiguously
revealed polyphyly of Opisthobranchia; therefore,
we decided to reconstruct the evolution of diet for
monophyletic Euthyneura and all main subclades
separately.
The ancestral gastropod in general is envisaged as
unselective (Vermeij and Lindberg, 2000). Carnivory
as well as herbivory might have arisen out of this
unspecific grazing by progressively selecting plant or
animal components of the food (Fretter et al., 1998). In
contrast to this, our results strongly support herbivory
as the ancestral state implying that carnivory evolved
several times independently. Furthermore, the ancestral
Euthyneuran was possibly not an unselective grazer.
Inclusion of the dubious opisthobranch subclade
Acteonoidea and its sister group Rissoelloidea does
145
not alter the overall tendency towards an herbivorous
last common ancestor. At first sight, this result
might seem to contradict parsimonious principles
because Acteonoidea, Nudipleura, and Umbraculida
(three basal clades of Euthyneura) are carnivores.
Thus, it would seem to be more parsimonious to
suggest carnivory as the ancestral diet preference.
Vermeij and Lindberg (2000) claim that the ancestral
gastropod was an unselective grazer by counting
evolutionary transitions from microphagy-carnivory
to herbivory and vice versa assuming the smaller
number to represent the more parsimonious pattern of
transition. We applied their method to our phylogeny
and counted evolutionary transitions from one state
to the other two in all possible directions only
considering major clades. These analyses confirm
herbivory as the most parsimonious ancestral feeding
mode, because the fewest evolutionary steps are
necessary for transition from herbivory to carnivory
as well as microphagy based on our phylogenetic
hypothesis. A possible explanation for our results is
that carnivorous species occur more clustered than
herbivores which are widespread all over clades. If
species revealing the same preferences are grouped
together, it takes only one evolutionary step to
switch from one state to another; whereas, multiple
transitions are necessary, if species occur separated
from each other. Thus, carnivory is not the most
possible ancestral state, although carnivorous clades
are predominantly found at the base of the tree. Based
on our phylogeny, herbivory is clearly preferred as the
ancestral mode of feeding for Euthyneura.
major marine animal phyla, except Echinodermata
(Willan, 1998b). This further specialization probably
contributes to the species richness especially in the
Nudibranchia subclade (~3000 species; Wägele and
Klussmann-Kolb, 2005). Several different diet-related
specializations have occurred in Nudibranchia.
The nudibranch subclade Aeolidoidea (member
of Dexiarchia) is able to store cnidocysts of their
cnidarian prey and use them for their own defence
(Kälker and Schmekel, 1976). This yielded to an
increase in food sources, since cnidarian colonies
could be fully explored and resulted in diversification
to more than 500 species in this subclade (Wägele,
2004). Other taxa of Aeolidoidea live in mutualistic
symbiosis with photosynthetic dinoflagellates and
make use of their metabolites (Burghardt et al.
2005). This specialization may also account for
the higher number of species in the respective taxa
(Wägele, 2004). The Chromodorididae (a taxon
of the nudibranch Anthobranchia) display a clear
pattern of food specificity at both genus and species
level (Rudman and Bergquist, 2007). They further
incorporate distasteful and anti-feedant secondary
metabolites of their prey into their skin or even into
special organs (MDF-mantle dermal formations) for
their own protection (Wägele, 2004; Wägele et al.,
2006; Rudman and Bergquist, 2007). The evolution
of these special mantle glands is regarded as the key
factor for extensive radiation of this clade, since the
storage in special organs might have led to feeding on
even more toxic sponges enhancing food resources
(Wägele, 2004).
The last common ancestors of the Acteonoidea/
Rissoelloidea clade as well as of Nudipleura
(representing the first offshoots in our study)
independently switched to a carnivorous life style.
While the Acteonoidea specialized on polychaetes
as a definite food item, the species-rich Nudipleura
further specialized on a variety of different and
seldom selected food sources of animal origin
like Porifera, Cnidaria, Bryozoa and Ascidiacea
which are partly unpleasant or toxic for most other
predators. In fact nudibranch diet encompasses all
In the future, it would be interesting to evaluate
if radiation of Nudipleura coincided with radiation
of some of their food items implying that Nudipleura
immediately adapted to existence of new sources. At
the moment, such an approach is hampered by the fact
that the age of the Nudipleura is unknown due to rare
fossil record and large credible intervals (~260-110
Mya / Dinapoli and Klussmann-Kolb, 2010; ~175-75
Mya / Göbbeler and Klussmann-Kolb, 2010, ~260-115
Mya / Jörger et al. 2010) in the only molecular clock
analyses incorporating this taxon.
146
The last common ancestor of Umbraculida,
Cephalaspidea, Aplysiomorpha, and Pteropoda
(Euopisthobranchia) possibly was herbivorous
although the (statistically not significant) first
offshoot is represented by the definitely carnivorous
Umbraculida.
The Cephalaspidea, Aplysiomorpha, and
Pteropoda are a morphologically well defined
taxon sharing an apomorphic feature related to diet:
the muscular oesophageal gizzard with gizzard
plates (Klussmann-Kolb and Dinapoli, 2006). The
possession of the gizzard with plates is probably
related to herbivory displaying the plesiomorphic
condition within this clade (Wägele, 2004;
Klussmann-Kolb and Dinapoli, 2006), an assumption
supported by the present study. The structure of the
gizzard differs among the taxa, it consists of at least
ten larger plates in the Aplysiomorpha, whereas the
Runcinacea and Thecosomata possess four plates
and a further reduction to three plates has occurred
in the Bulloidea and other Cephalaspidea. Wägele
(2004) assumed that evolution of three large plates
allowed a higher diversification through exploration
of different kinds of food causing higher diversity in
the bulloid Cephalaspideans (~260 species) than in the
Aplysiomorpha (~75 species).
The last common ancestor of the Cephalaspidea
(without Runcinacea) was possibly also an herbivore.
Cephalaspideans feed on a variety of different
food items and carnivory has possibly evolved at
least twice during evolution of this clade which
is in accordance with a former character tracing
analysis in Cephalaspidea (Malaquias et al., 2009a).
Both herbivorous (Bulloidea) and carnivorous
(Philinoidea) subclades display rich species diversity
(about 260 and 500 species respectively/Wägele,
2004) underlining evolutionary success of both
groups specializing in different diets. Both feeding
strategies benefit from the evolution of a highly
specialized gizzard with three plates displaying the
key character for higher diversity in Cephalaspidea
(Wägele, 2004).
The Aplysiomorpha and Pteropoda form a clade
with herbivory as strongly supported ancestral diet,
however ancestral Pteropoda expanded their food
sources. Carnivory is here favoured as the ancestral
diet, but herbivory and unselective sources cannot be
excluded. Thus, the last common ancestor of the whole
clade possibly grazed on algae like extant aplysiomorph
species and change to pelagic life style in Pteropoda
was followed by exploration of new food sources. It is
possibly not effective to be restricted to a certain food
source if living in the pelagial with limited abilities of
self navigation. Otherwise, the Thecosomata possess a
gizzard which is probably related to herbivorous diet
preferences (Klussmann-Kolb and Dinapoli, 2006).
Thus, herbivory might be the ancestral condition for
all Pteropoda and Gymnosomata changed to carnivory
accompanied by loss of the gizzard.
The Aplysiomorpha also exhibit special
adaptations to their prey. Some taxa produce a purple
“ink” out of pigments ingested with the algae they
feed upon used to deter predators (Willan, 1998a).
Most species sequester secondary metabolites of
algae in their digestive gland; however if these are
used for defensive behavior (Wägele et al., 2006) or
not (Pennings, 1994) is disputed.
The last common ancestor of Pulmonata,
Sacoglossa and Acochlidiacea probably also was
an herbivore. However, there seems to be a trend to
unselective feeding especially in freshwater species.
The Sacoglossa are highly specialized algal
feeders and the evolution of a special tooth for
cutting algal cell walls is regarded as essential
for their radiation (Wägele, 2004; Händeler et al.,
2009). Moreover, some sacoglossans are able to store
chloroplasts of their food items and make use of the
produced metabolites (Rumpho et al., 2000), which
is a possible further key character for evolution of
this taxon (Wägele, 2004; Händeler et al., 2009). Our
results suggest that the last common ancestor of the
Sacoglossa already fed upon algae and developed the
specialized features enabling radiation of the clade.
147
In summary, our study demonstrates that the
diverse dietary strategies of the opisthobranch
subclades most probably evolved from an herbivorous
ancestral state and were established in the different
lineages. This contradicts previous assumptions that
carnivory was the plesiomorphic feeding preference
in Opisthobranchia (Haszprunar, 1985). Furthermore,
the results of the present study indicate that
interactions of prey structure, habitat, and anatomy
might not have had a strong influence on phylogeny
of the whole clade, but were probably accounting for
the diversification within the subclades as already
claimed for the Cephalaspidea (Malaquias et al.,
2009a).
CONCLUSIONS
Our phylogenetic analyses yield some intriguing
insights into the phylogeny of euthyneuran gastropods.
The Opisthobranchia are undoubtedly rendered
polyphyletic. The single monophyletic lineages of
Nudipleura, Sacoglossa and Acochlidiacea evolved
more or less independently, while the Umbraculida,
Cephalaspidea, Aplysiomorpha and Pteropoda
(Euopisthobranchia) form a well supported clade.
Herbivory as most likely ancestral diet of all
Euthyneura is clearly supported by our analyses
implying that carnivory evolved several times
independently in the different subclades. While the
exploration of new diets coincide with adaptive
radiation in some clades, like carnivory in Nudipleura
or different herbivorous as well as carnivorous food
items in Cephalaspidea, species numbers of other
clades, like the Umbraculida which also changed to
carnivorous diet, remained limited.
Thus, it seems possible that dietary preferences
along with exploration of new diet resources might
have supported the evolutionary success of different
lineages. However, diet is clearly only one of probably
many features responsible for the success of a certain
clade and a closer look at other possibly important
148
characters and their evolution in Euthyneura is
necessary to fully understand the evolution of this
taxon. Moreover, disentangling the interrelationships
of the well defined subclades of Euthyneura needs
further research. For this purpose new marker genes
are irreplaceable since resolution is too low with the
conventional ones.
ACKNOWLEDGEMENTS
The German Academic Exchange Service
(DAAD) financially supported a collecting trip to
Australia for the first author. Permission for collecting
was given by the NSW Department of Primary
Industries (permit number p07/0058).
Georg Mayer (Melbourne), John Healy (Brisbane)
and Angela Dinapoli (Frankfurt) provided help during
the field trip to Australia.
DNA samples or specimens were provided by
Heike Wägele and Katharina Händeler (Bonn),
Michael Schrödl and Enrico Schwabe (Munich) as
well as Patrick Krug (Los Angeles).
Heike Wägele (Bonn) and Michael Schrödl
(Munich) made valuable comments on an earlier
version of this manuscript. Jan Müller (Frankfurt)
assisted in literature research of dietary preferences.
The second author is supported by the Biodiversity
and Climate Research Centre (BiK-F), Frankfurt/Main.
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Thalassas, 27 (2): 155-168
NUDIBRANCH FEEDING BIOGEOGRAPHY:
ECOLOGICAL NETWORK ANALYSIS OF
INTER- AND INTRA-PROVINCIAL VARIATIONS
HANS BERTSCH(1)
Key words: Nudibranchs, feeding biogeography, long-term density field studies, distribution and abundance
ABSTRACT
Timed nudibranch-density studies were
performed in four different central and eastern Pacific
zoogeographic provinces: Hawaiian, Oregonian,
Sea of Cortez and Mexican. Densities and relative
percentages of species and specimens observed were
compared with all known species recorded from
each faunal province to determine the functional
structures of nudibranch community networks. There
were greater correlations of nudibranch abundances
by feeding preference between provinces than from
sites within a province. Diversity (Shannon-Wiener H’
and Pielou’s J’ evenness) indices revealed contrasting
patterns for bryozoan, cnidarian and sponge feeder
abundances. At all levels, variation varies, resulting in
complexly different relationships.
(1) Instituto de Investigaciones Oceanológicas,
Universidad Autónoma de Baja California, Ensenada,
BC, México .
[email protected]
INTRODUCTION
Traditional marine biogeographic analyses have
emphasized the occurrence of genera or species in
faunal provinces. Key components of ecological
differences between provinces include endemism,
barriers, latitudinal gradients, and vertical/horizontal
distributions (summaries in, e.g., Pielou, 1979; Briggs,
1974 and 1995; Cox & Moore, 2010). Historical
biogeography has viewed these themes over time
(e.g., Rex et al., 2005; Jablonski et al., 2006), analyzed
abundance data in the fossil record (Kidwell, 2001,
and other thanatocoenoses), and used phylogenetic
and molecular methodologies (e.g., Dick et al., 2003;
Rocha et al., 2007).
Opisthobranch biogeographic studies have also
mainly emphasized genus/species biodiversity patterns
in faunal regions (e.g., Marcus & Marcus, 1967;
Gosliner, 1992; Bertsch, 1993, 2009 and 2010; Jensen,
2007; García, Domínguez & Troncoso, 2008; Garcia
& Bertsch, 2009; Trowbridge, 2002; Trowbridge et
al., 2010). Broad thematic zoogeographic comparisons
have been published on developmental modes (Clark &
Goetzfried, 1978; Jensen, 2003; Goddard & Hermosillo,
155
HANS BERTSCH
A
B
C
Figure 1:
Correlation between observed percentages of species and specimens.
A. Bryozoan feeders, no correlation; P = 0.144. B. Cnidarian feeders, strong positive correlation; y = 0.483x + 22.75, P < 0.001.
C. Sponge feeders, strong positive correlation; y = 0.512x + 19.14, P < 0.001.
2008). Especially noteworthy are phylogeographic
studies on the cephalaspidean genus Bulla (Malaquias
& Reid, 2009), the “Pleurobranchomorpha” (Göbbeler
& Klussmann-Kolb, 2010), dorids (Valdés, 2004), and
the chromodorid Hypselodoris (Gosliner & Johnson,
1999; Alejandrino & Valdés, 2006).
However, none of these opisthobranch studies
were based on densities of the reported species,
despite the prescient caveat of Gosliner (1987: 13):
“In studying the biogeography of an area it is not
adequate to simply know what species are present
or absent in that region. One must know what
156
ecological role a species plays within a locality.
Some idea of its abundance and prey/predatory
relationships help ascertain the impact of a single
species in a particular area.” Long-term longitudinal
studies are essential to determine relative abundance
and biodiversity variations, population extinctions,
habitat degradation, climate-effected changes and
conservation priorities, in addition to elucidating
the functional structures underlying biogeographic
patterns (e.g., European birds, Jonzén et al., 2006;
Mexican lizards, Sinervo et al., 2010; Californian
nudibranchs, Schultz et al., 2011; northeast Pacific
kelp forests, Dayton et al., 1992).
ECOLOGICAL NETWORK ANALYSIS OF INTER- AND INTRA-PROVINCIAL VARIATIONS
A
B
C
D
Figure 2:
Percentages of species and density of cnidarian feeders correlated with total site evenness (J’) and diversity (H’).
A. Percent of specimens and total site diversity; y = 38.1x -61.32, P = 0.002. B. Percent of specimens and total site evenness; y = 147.5x -59.62, P =
0.004. C. Density of cnidarian-feeding specimens and total site diversity; y = 10.01x -16.16, P = 0.014.
D. Density of specimens and total site evenness; y = 42.18x -17.18, P = 0.019.
This methodology has been previously used
(Trowbridge et al., 2009) for several species of Japanese
sacoglossan opisthobranchs: Placida, Elysia, and
Stiliger spp. They combined long-term field surveys
measuring density (spring and summer, 2000-2004)
with laboratory feeding preference experiments, to
determine interaction webs (or networks), contrasted
with other biogeographic regions at comparable high
latitudes.
Network theory examines the underlying
connectivity and topology within complex systems
which have evolved through “mechanisms beyond
randomness” (Barbási, 2009: 413). The species
composition of a community or larger provinciallevel region has a functional architecture (Bascompte,
2009) of ecological interactions. Simply stated, its
structure works.
Because food webs are central to ecology, trophic
diversity provides greater understanding of the
structure of ecological networks than taxonomic
relationships (Pascual & Dunne, 2006; Bascompte,
2009). As “the main driving force for change in
community structure and coevolution of species
within an environment” (Mondal et al., 2010: 137),
157
HANS BERTSCH
A
B
C
D
Figure 3:
Percentages of specimens and species of sponge feeders, correlated with evenness and diversity.
A. Percent of specimens and total site diversity; y = -34.76x + 132.2, P = 0.05. B. Percent of specimens and total site evenness; y = -158.7x + 145.6,
P = 0.022. C. Percent of species and evenness distribution among sponge-feeding species; y = -84.26 x + 96.66, P = 0.003. D. Percent of specimens
and evenness distribution among sponge-feeding species; y = -157x + 146.6, P = 0.002.
predation has a critical role in forming biogeographic
patterns. Long-term density field studies, identifying
abundance of predator guilds, can analyze the behavior
of these networks comparably across different
nudibranch communities and faunal provinces.
Bertsch & Hermosillo (2007) used 3 long-term
studies of opisthobranch abundance and natural
history to correlate biodiversity differences with
ecosystem trophic structures. Along the California
coast, Goddard et al. (2011) have documented
climatic-related changes in the distribution and
feeding patterns of the aeolid nudibranch Phidiana
158
hiltoni (O’Donoghue, 1927). This paper analyses the
feeding biogeography of nudibranchs from 9 central
and east Pacific sites (across 4 different marine
provinces), based on long-term studies of abundance,
to determine variation patterns in the tropic networks
at different ecological scales (from community to
province).
Long-term comparable site studies of nudibranch
densities are not common. The pioneering species
lists of opisthobranchs occurring in various California
Table 1: Sampling sites
Region, Site, Approximate Lat & Long
Hawaiian1
Kewalo/Magic Island, Oahu
21º 17' N; 157º 50' W
Makua, Oahu
21º 33' N; 158º 13' W
Pupukea, Oahu
21º 35' N; 158º 06' W
Oregonian2
North Cove, Cape Arago, Oregon
43º 20' N; 124º 22' W
Middle Cove, Cape Arago
43º 20' N; 124º 22' W
Scott Creek, California
37º 01' N; 122º 13' W
Asilomar, California
36º 36' N; 121º 57' W
Sea of Cortez3
Islas, Bahía de los Ángeles
28º 59' N; 113º 29' W
Gringa/Cuevitas, BLA
29º 03' N; 113º 32' W
Mexican4
Grupo 1, Bahía de Banderas
20º 42' N; 105º 34' W
20º 33' N 105º 17' W
Search hours
Searches
Dates
99.5
67
11/1977-12/1985
158.0
79
11/1977-12/1985
74.75
37
3/1978-10/1987
[no time]
20
4/1984-7/2008
[no time]
10
7/1980-7/2008
171.32
56
6/1975-1/2010
43.5
13
11/2007-5/2010
52.64
52
1/1992-12/2001
229.3
211
1/1992-12/2001
233.4
142
4/2002-4/2005
511.8
214
4/2002-4/2005
1
Data by Scott Johnson (Hawaii, USA)
Data by Jeffrey Goddard (Oregon and California, USA)
Data by Hans Bertsch (Baja California, México)
4
Data by Alicia Hermosillo (Jalisco/Nayarit, México); from Hermosillo, 2006
2
3
counties described their presence as “rare” or “frequent”
(Sphon & Lance, 1968; Roller & Long, 1969; Gosliner
& Williams, 1970), or did not correlate numbers of
specimens with a precisely measurable dimension
(Bertsch et. al., 1972; specimens recorded as numbers
in each month, not per unit of collecting effort).
Ecological density studies of nudibranchs have
correlated numbers/area for particular species whose
life history is amenable to such a measure (Todd,
1981; Johnson, 1983). Narrowly directed studies have
measured density per unit area of prey (e.g., Bertsch,
1989, and pers. obser.) or grams of slugs per gram
of prey (e.g., Clark, 1975). Because of how diversely
nudibranchs (and opisthobranchs in general) occur
in an ecosystem, broadly applying these techniques
across multiple taxa can result in a faulty and quite low
level of abundance for the opisthobranch community.
The preferred density measure for all nudibranchs and
allies throughout a diverse habitat is a timed-search
methodology (Nybakken, 1974 and 1978; Clark,
1975), which yields internally and externally (both
within and between sites and observers) comparable
and consistent data. It also allows searching all
habitats within the site across which the assorted
nudibranch feeding patterns occur.
Timed density studies (each averaging about 1 hour)
were performed in four different central and eastern
Pacific zoogeographic provinces (sensu Briggs, 1995):
Hawaiian [HA], Oregonian [OR], Sea of Cortez [SC],
and Mexican [MX]. Each consisted of multiple years,
spanning all months and seasons. These data provided
actual abundances of both species and specimens in
the multiple habitats at each site. Table 1 identifies the
study sites with dates and times and observers’ efforts.
159
HANS BERTSCH
Table 2:
Reported taxa1 and feeding preferences in the biogeographic provinces Oregonian, Sea of Cortez, Mexican and Hawaiian. Numbers of known
species of each higher taxon or feeding preference reported to occur in each province, and percentages of known species and the observed
specimens in this study. Percentages of feeding preferences do not add up to 100%; annelid, ascidian, crustacean, kamptozoan, opisthobranch and
opisthobranch egg feeders not included.
Oregonian
Taxa
Doridina
55 53.4%
Arminina
6 5.8%
Dendronotina
15 14.6%
Aeolidina
27 27.2%
Total Species: 103
Sea of Cortez
Mexican
Hawaiian
65 56%
4 3.4%
13 11.2%
34 29.3%
116
57 47.9%
2 1.7%
17 14.3%
43 36.1%
119
117 65.7%
2 1.1%
8 4.5%
51 28.7%
178
Feeding Preferences (known species)
Bryozoans
27 26.2%
21 18.1%
Cnidarians
43 41.7%
48 41.4%
Sponges
29 28.2%
42 36.2%
16 13.4%
59 49.6%
40 33.6%
17 9.5%
55 30.9%
89 50%
Feeding Preferences (observed specimens)
Bryozoans
2910 25.3%
602 15%
Cnidarians
5614 48.8%
1198 29.9%
Sponges
3171 27.6%
2171 54.1%
Totals:
11,497
4011
2336 11.8%
38 0.3%
11,335 57.3%
395
3.2%
5422 27.4% 11,511 94.2%
19,775
12,222
1
Based on distribution records in Behrens & Hermosillo (2005), Hermosillo, Behrens & RíosJara (2006), Gosliner, Behrens & Valdés (2008), Bertsch (2010), and recent species descriptions.
Locality maps and site descriptions are available in:
Johnson (1983 and 1989) and Bertsch & Gosliner, 1989,
[HA]; Nybakken, 1978, Goddard, 1984, and Schultz et
al., in press, [OR]; Bertsch, Miller & Grant, 1998, [SC];
and Hermosillo, 2006 [MX].
Densities of all species were calculated and
analyzed based on the major prey items (Bryozoa,
Cnidaria, Porifera). Multiple comparisons and
correlation analyses were performed on these data sets
to determine structural relationships between percent
of species, percent of specimens, and Shannon-Wiener
H’ and Pielou’s J’ evenness values (both within a prey
group and across all prey groups, i.e, the total site).
These were also compared with all known nudibranch
species from each zoogeographic province, based on
the faunal guide summaries referenced in Table 2.
RESULTS
Reported numbers of species vary from similar
numbers in the 3 eastern Pacific regions (103-119
species) to a high of 178 species in the Hawaiian
province (Table 2). The subordinal taxonomic
160
composition is similar in OR and SC (Likelihood ratio
G-test, G = 1.4, 3 df, P = 0.703). There is a marginally
significant difference in dorid representation among
regions (G = 10.2, 3 df, P = 0.071) with the most in
HA. The other three regions exhibited no significant
difference in dorid representation (G = 1.6, 2 df, P =
0.444). There was no significant difference in aeolid
representation among regions (G = 3.0, 3 df, P = 0.397)
with 30% of the recorded nudibranchs being aeolids.
Dendronotid representation varied among regions (G
= 11.8, 3 df, P = 0.008) with the lowest percentage of
dendronotids in HA (Table 2). The arminids (sensu
lato, I acknowledge the polyphyly of this taxon) are
consistently the lowest percentage of species present:
overall 2.7% of the nudibranchs recorded (Table 2).
Overall, 17% of the species (12% of the individuals)
fed on bryozoans, 42% (40%) fed on cnidarians, and
41% (48%) fed on sponges. However, the community
composition of nudibranch feeding preferences (Table
2) differed markedly both among the four provinces
numerically at the species level (G = 27.7, 6 df, P
<0.001) as well as at the specimen or individual level
(G = 9.977, 6 df, P <0.001).
Table 3:
Comparative abundance (percentages) of individual specimens (Ind) and species (Spp) of nudibranchs observed, according to feeding preference.
Data sources as in Table 1.
Province and Site
Bryozoans
Ind
Spp
Hawaiian
Kewalo/Magic Island, Oahu
Percentages of:
Cnidarians
Ind
Spp
Sponges
Ind
Spp
0.09
2.3
7
25.6
84.5
62.8
Makua, Oahu
0.1
4.6
1.4
18.5
98.4
70.8
Pupukea, Oahu
1
3
3
18
95.6
75.8
61.8
26.3
29.6
42.1
20.2
31.6
4.5
20
77.6
54.3
18.5
28.6
Scott Creek, California
18.8
25
54.6
50
26.4
25
Asilomar, California
26.2
19.4
29.1
41.7
48.1
36.1
Sea of Cortez
Islas, Bahía de los Ángeles
77.2
26
8.8
31.6
10.4
36.8
Gringa/Cuevitas, BLA
4.9
17.2
33.2
35.9
61.1
43.8
Mexican
30.6
9.9
46.3
51.9
21.4
33.3
3.4
13.6
63
51.5
31.2
30.1
Oregonian
North Cove, Cape Arago
Middle Cove, Cape Arago
Between and within province variation
There is no predictable relationship nor correlation
between % of all known species reported for each
region and % of observed specimens (Table 2) for
the 4 provinces during timed and density/abundance
structural studies. The percentages can be either
the same (bryozoan and sponge feeders in OR),
higher (cnidarian feeders in SC), or lower (cnidarian
feeders in MX). Regardless of province, the bryozoan
feeding nudibranchs always represented the lowest
percentages of both species and specimens (Table 3).
However, contributions to the community structure
by absolute numbers, rather than relative percentages
of species and specimens, give different perspectives.
If absolute numbers are investigated, there is a highly
significant correlation between number of known
species and observed specimens (Pearson correlation,
r = 0.718, P = 0.008, N = 12). The bryozoans
are lowest in terms of numbers of species (1-way
ANOVA, F = 4.71, 2 df, P = 0.040) but not for numbers
of specimens (i.e., no statistical difference among
prey types: F = 1.24, P = 0.334, 2 df). This pattern
is still seen if we delete the two cases (Hawaii) with
potentially undue influence (r = 0.716, P = 0.020, N =
10). These raw abundance data of specimens do not
account for differences in collecting effort, but form
the basis for the density and percentage figures which
are comparable between and within provinces.
Table 3 shows the comparative abundance of
specimens and species by feeding preference at
the study sides in each province. At the four OR
sites, despite similar species percentages (19–26%),
specimen abundance of bryozoan feeders fluctuated
greatly (4.5–61.8%). Similar disparities occur in SC
(between the Islas and Gringa/Cuevitas sites) and MX
(between Grupos 1 and 2). Within region variation
(community differences) is as great as that between
or among regions (province level).
161
HANS BERTSCH
Cnidarian predator abundance is lowest in HA,
for both percentages of reported species and observed
specimens. Their highest abundance was found in
MX (49.6% of known species, 57.3% of observed
specimens). These patterns were not seen at the
intermediate percentages reported for OR and SC.
Although both provinces have the same % of known
species (41.7% and 41.4%), the 48.8% abundance
of specimens at OR was far greater than the 29.9%
abundance at SC. These fluctuating variations show
no latitudinal gradient.
As shown in Table 3, within HA the sites showed
little variation in both percentages of known cnidarian
feeding species found (18.5–25.6%) and of observed
specimens (1.4–7%). The OR sites only varied from
41.7–54.8% of known species found, but showed a
large change in observed specimens (29.1–77.6%).
Although the highest density of cnidarian feeders
inversely corresponded with the lowest density of
bryozoan feeders at Middle Cove, no relationship
existed between the similarly dense (29.1% and 29.6%)
cnidarian feeders and the highest and mid density
bryozoan feeding communities (61.8% and 26.2%)
at North Cove and Asilomar. In a curious opposition
among the provinces of the larger Panamic province
(sensu Keen, 1971), at MX study sites, cnidarian
feeders were most common, but not so at the SC sites,
regardless of the bryozoan feeder density.
Sponge feeders showed the highest percentages
of densities in HA and SC (Table 3). This relationship
held for all 3 HA sites, but only at the Gringa/
Cuevitas SC location (which had the lowest density of
bryozoan feeders).
Diversity variations in density/abundance based on
feeding preference
Combining the data from all sites (Table 4), I
calculated the relationships between abundance and
diversity for each of the 3 major nudibranch feeding
preferences, using correlation analyses for 11 pairs of
measurements (Table 5).
162
Bryozoan feeders (Fig. 1a) showed no correlation
(P = 0.144) between observed % of species and
specimens. Higher percentages of specimens did
not correspond to higher numbers of species. In OR
sites, specimen abundances of 61.8% and 18.8%
had nearly the same species abundances (26.3% and
25%). The highest specimen percentages at SC and
MX sites were found oppositely with the highest and
lowest percentages of species abundance. None of the
correlation analyses performed (Table 5) resulted in a
statistically significant relation for bryozoan feeding
nudibranchs.
In contrast, there is a positive correlation between
percentages of found species and specimens for both
cnidarian (Fig. 1b, P < 0.001) and sponge (Fig. 1c, P <
0.001) feeding nudibranchs.
Cnidarian feeders showed a positive correlation
between the H’ diversity and evenness indices with
both percent of specimens found and density (Fig.
2a, %Specimens/Total Site H’, P = 0.002; Fig. 2b,
%Specimens/Total Site Evenness, P = 0.004; Fig. 2c,
Density/Total Site H’, P = 0.014; and Fig. 2d, Density/
Total Site Evenness, P = 0.019). As more species
and specimens were found, diversity and evenness
increased similarly. This relation means that the
increasing effect was spread across many species,
not just a super-abundance of a few, as among the
bryozoan feeders.
Sponge feeders exhibited a totally opposite
relationship. There was a negative correlation between
percent of specimens found and the total site H’ (Fig.
3a, P = 0.052) and evenness (Fig. 3b, P = 0.023)
indices. The evenness of distribution (calculated for
just the sponge feeding community) of both percent of
species (Fig. 3c, P = 0.003) and specimens found (Fig.
3d, P = 0.003), also showed a statistically significant
negative correlation. The more species and specimens
found, the lower were the diversity and evenness.
This reflects the extreme abundance of a single or few
species. For instance, at both the Makua and Pupukea
HA sites, Glossodoris rufomarginata (Bergh, 1890)
Table 4:
Totals of species and specimens observed (including numbers, percentages, and densities), and H’ and evenness (J’) values for provinces and
for feeding preferences within each site. Totals are for all specimens observed, including predators of ascidians, crustaceans, kamptozoans,
opisthobranchs and opisthobranch eggs
Location/Prey
Hawaiian
Kewalo &
Magic Island
Br (0.03/hr)
Cn (2.25/hr)
Sp (27.26/hr)
Makua
Br (0.04/hr)
Cn (0.6/hr)
Sp (40.86/hr)
Pupukea
Br (0.37/hr)
Cn (1.02/hr)
Sp (31.34/hr)
Species
%
Specimens
%
43
(0.43/hr)
1
11
27
2.3%
25.6%
62.8%
3209
(32.35/hr)
3
224
2712
0.09%
7%
84.5%
65
(0.41/hr)
3
12
46
6563
(41.54/hr)
4.6%
7
18.5%
95
70.8% 6456
66
(0.88/hr)
2
12
50
2450
(32.78/hr)
3%
28
18%
76
75.8% 2343
H'
Evenness
2.087
0.555
—
1.341
1.694
—
0.559
0.514
1.354
0.324
—
1.658
1.258
—
0.667
0.329
2.002
0.478
1%
3%
95.6%
—
1.594
1.82
—
0.641
0.465
0.1%
1.4%
98.4%
Oregonian
North Cove,
Cape Arago
Br
Cn
Sp
38
10
16
12
26.3%
42.1%
31.6%
1783
1102
527
360
61.8%
29.6%
20.2%
2.522
1.306
1.992
1.826
0.693
0.567
0.719
0.735
Middle Cove,
Cape Arago
Br
Cn
Sp
35
7
19
10
20%
54.3%
28.6%
1070
48
830
198
4.5%
77.6%
18.5%
2.795
1.784
2.277
1.822
0.786
0.858
0.773
0.791
Scott Creek
Br (7.62/hr3)
Cn (22.09/hr)
Sp (10.71/hr)
Asilomar
Br (10.44/hr)
Cn (10.85/hr)
Sp (17.91/hr)
Sea of Cortez
BLA Islands
Br (8.18/hr)
Cn (0.93)
Sp (1.1/hr)
BLA Gringa/Cuevitas
Br (0.75/hr)
Cn (5.01/hr)
Sp (9.22/hr)
Mexican
BB Grupo 1
Br (8.0/hr)
Cn (12.09/hr)
Sp (5.58/hr)
BB Grupo 2
Br (0.92/hr)
Cn (16.64/hr)
Sp (8.05/hr)
48
(1.19/hr)
12
24
12
6938
(40.497/hr)
1306
3785
1834
2.674
0.691
25%
50%
25%
18.8%
54.6%
26.4%
1.622
1.498
2.057
0.653
0.471
0.828
36
(0.827/hr)
7
15
13
1706
(39.22/hr)
454
472
779
2.812
0.785
19.4%
41.7%
36.1%
26.2%
29.1%
48.1%
1.021
1.866
2.089
0.524
0.689
0.815
38
(0.72/hr)
10
12
14
558
(10.6/hr)
431
49
58
1.907
0.524
26%
31.6%
36.8%
77.2%
8.8%
10.4%
0.941
2.034
2.106
0.409
0.818
0.798
64
(0.279/hr)
11
23
28
3453
(15.06/hr)
171
1149
2113
2.538
0.61
17.2%
35.9%
43.8%
4.9%
33.2%
61.1%
1.83
2.113
1.465
0.763
0.674
0.44
81
(0.374/hr)
8
42
27
6068
(25.998/hr)
9.9% 1867
51.9% 2821
33.3% 1303
2.891
0.658
30.6%
46.3%
21.4%
0.656
2.441
2.058
0.315
0.653
0.624
103
(0.2/hr)
14
53
31
13707
(26.78/hr)
13.6% 469
51.5% 8514
30.1% 4119
3.406
0.735
1.516
2.798
2.219
0.574
0.705
0.646
3.4%
63%
31.2%
163
HANS BERTSCH
Table 5:
Data sets on which correlation analyses were performed; feeding preference groups for which statistically significant values were obtained, are in
parentheses (Br = bryozoan; Cn = cnidarian; Sp = sponge). Significant values given in Figures 1-3.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
% Species / % Specimens
% Specimens / H’
% Specimens / Evenness
% Species / H’
% Species / Evenness
% Density / H’
% Density / Evenness
Density / Total Site H’
Density / Total Site Evenness
% Specimens / Total Site H’
% Specimens / Total Site Evenness
(Cn, Sp)
(Sp)
(Sp)
(Cn)
(Cn)
(Cn, Sp)
(Cn, Sp)
represents 73.2% and 53.9% of all sponge feeders and
at the Gringa/Cuevitas SC site Doriopsilla gemela
Gosliner, Schaefer & Millen, 1969, represents 58.2%.
In contrast, there is no single species representing
over 50% of the cnidarian feeders at any site.
2 and Gosliner et al., 2008). Species of bryozoan
feeders in HA account for 9.5% of the known
nudibranch fauna, but timed searches yielded only
2.3–4.6% of species found, with actual density below
1% of the specimens.
DISCUSSION AND CONCLUSIONS
The extremely high abundance of bryozoan
feeders at 3 OR, SC and MX sites (61.8%, 77.2% and
30.6%, respectively), in contrast to adjacent sites with
low abundance (4.5%, 4.9% and 3.4%), is accounted
for by only 2 species at each site: Janolus fuscus
(O’Donoghue, 1924) and Triopha catalinae (Cooper,
1863) at North Cove, Cape Arago, and Tambja abdere
Farmer, 1978, and T. eliora (Marcus & Marcus, 1967)
at both Islas, BLA, and Grupo 1, Bahía de Banderas.
The habitat and prey communities also differ between
these sites of high and low abundance. At Cape
Arago, nudibranchs mainly occur on the undersides
of boulders and ledges (Goddard, 1984). North Cove
has the largest intertidal area of the sites samples, and
the highest abundance of species and individuals. In
contrast, Middle Cove has a high density of cnidarian
and sponge prey, and the higher densities (both
species and specimens) of their nudibranch predators
(Table 3). The SC and MX sites of Islas and Grupo 1
are both characterized by more exposed, cliff-faced,
exterior bay habitats, with a healthy coverage of
the sessile cheilostomate Cellulariomorpha bryozoan
prey Sessibugula translucens Osburn, 1950. These
characteristics are lacking at the adjacent Gringa/
Cuevitas and Grupo 2 sites (Bertsch, pers. obser., and
Hermosillo, 2006).
Different high or low densities of bryozoan,
cnidarian and sponge feeders vary independently
even between nearby sites separated by less than a half
degree of latitude, and are not predictable by province.
It should be noted that differences are not attributable
to intertidal vs. subtidal variations, because within
province variations of each encompass the entire
range of diversity and density patterns found.
Although numbers of species of nudibranch
bryozoan feeders have been reported to have a
latitudinal cline (highest in Great Britain, South
Africa and “California,” see Gosliner, 1992), the
pattern is not that precise. Since bryozoan feeders
demonstrate abundance differences between and
within many temperate and tropical provinces, a
“cline” may not be the most appropriate description of
these variations. Bryozoan feeders represent 26.2%,
18.1% and 13.4% of the nudibranch species in OR, SC
and MX respectively (Table 2); they are 18% and 14%
of the Californian (sensu Briggs, 1974) and Caribbean
(=tropical northwestern Atlantic, sensu Valdés et al.)
faunas. They represent an even lower % of species
across the Indo-Pacific and HA provinces (Table
164
Seeking generalizations, i.e, ecological laws
or patterns at the community level is inherently
difficult both because of their “local” nature and
the diversity of variation in the fundamental units
studied (Simberloff, 2004). Broader comparisons
at provincial or global levels for wider or narrower
taxonomic or ecological units (e.g., specific phyla,
classes or families, or multi-taxa communities) are
even harder and less convincing, often fraught with
exceptions that seemingly disprove the rule. However,
using an analysis of feeding networks, this paper has
shown the existence of such variation within and
between provinces. At all levels, variation varies,
resulting in complexly different relationships.
importance of such long-term natural history studies
for conservation cannot be overemphasized (Dayton,
2003).
Size matters (Willis & Whitaker, 2002; McGill,
2010). Network theory and interaction webs address
the role of scale dependency. This is true for coral reef
biodiversity across regions of the Indian and Pacific
Oceans (Bellwood & Hughes, 2001; Knowlton, 2001).
I have shown this to be true also for nudibranch
communities within and between 4 eastern and central
Pacific provinces, having compared and contrasted
the network variations of nudibranch abundance by
prey specificity.
Alejandrino, Alvin & Ángel Valdés. 2006. Phylogeny
and biogeography of the Atlantic and eastern Pacific
Hypselodoris Stimpson, 1855 (Nudibranchia,
Chromodorididae) with the description of a new species
from the Caribbean Sea. Journal of Molluscan Studies
72 (2): 189-198.
Barabási, Albert-László. 2009. Scale-free networks: a
decade and beyond. Science 325 (5939): 412-413.
Bascompte, Jordi. 2009. Disentangling the web of life.
Science 325 (5939): 416-419.
Bellwood, David R. & Terry P. Hughes. 2001. Regionalscale assembly rules and biodiversity of coral reefs.
Science 292 (5521): 1532-1534.
Bertsch, Hans. 1989. Life history of the intertidal Californian
nudibranch Hopkinsia rosacea MacFarland, 1905.
Western Society of Malacologists, Annual Report 21:
19-20.
Bertsch, Hans. 1993. Opistobranquios (Mollusca) de la costa
occidental de México. In: S.I. Salazar-Vallejo & N.E.
González (eds.), Biodiversidad Marina y Costera de
México. Comisión Nacional de Biodiversidad y CIQRO,
México. pp. 253-270.
Bertsch, Hans. 2009. Book review of Indo-Pacific
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Bertsch, Hans. 2010. Biogeography of northeast Pacific
Network theory “can address the inherent
heterogeneity in who meets whom” (Bascompte, 2009:
419). The actual contribution of species to community
ecosystems differs among feeding preferences and
between faunal provinces, variously shaped by
trophic patterns acting on dispersal and vicariance
events. “They don’t choose their neighborhood, but
they choose who their neighbors are” (Rosa Campay,
pers. comm.). They may also change their feeding
relationship with their neighbors, as Phidiana hiltoni
has done (Goddard et. al., 2011).
These long-term density studies on large ecological
networks provide functional information on the trophic
interrelations of nudibranch biodiversity. It would be
remiss to not comment on their broader significance.
Given the enormous environmental degradation of
our global ecosystems by anthropogenic means, the
ACKNOWLEDGMENTS
I am grateful to Cynthia D. Trowbridge for
various statistical analyses within this paper, and for
her critical readings of multiple drafts. Jeffrey H. R.
Goddard and Scott Johnson graciously allowed me
to use their unpublished long-term data sets from
Oregon, California and Hawaii.
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Thalassas, 27 (2): 169-192
COMPARATIVE MORPHOLOGY OF THE MANTLE CAVITY
ORGANS OF SHELLED SACOGLOSSA, WITH A DISCUSSION
OF RELATIONSHIPS WITH OTHER HETEROBRANCHIA
KATHE R. JENSEN(1)
Key words: Shelled Sacoglossa, mantle complex, comparative morphology, Heterobranchia, Mollusca
ABSTRACT
The mantle cavity and pallial structures of
18 species from 8 genera of shelled Sacoglossa
(Mollusca, Opisthobranchia) have been examined and
compared with literature information about several
taxa of Heterobranchia. Recent molecular studies
have indicated an affiliation of the Sacoglossa and
the Siphonariidae, a family of intertidal limpets
usually referred to basommatophoran Pulmonata. The
gill of shelled Sacoglossa is unique within the taxa
usually referred to Opisthobranchia by its attachment
to the surface of the kidney. Morphologically the
sacoglossan gill is similar to that of siphonariids, but
the latter is located behind the kidney. The heart of
shelled Sacoglossa is almost completely detorted.
This also differs from other basal heterobranch
taxa. In the shelled Sacoglossa the inconspicuous
(1) Zoological Museum (Natural History Museum of Denmark),
Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark
E-mail: [email protected]
osphradium is closely associated with shell adductor
or cephalic/ pharyngeal retractor muscles, indicating
that it is associated with the closure of incurrent water
flow to the mantle cavity. The genera Cylindrobulla,
Ascobulla and Volvatella are unique in having a
long narrow section of the aperture between the
anterior incurrent opening and the posterior excurrent
opening. This section forms a functional separation
of water currents and is lined by a row of glandular
bosses. In conclusion the Sacoglossa definitely stand
out from opisthobranch taxa, but the similarities with
siphonariids are superficial and may be explained as
homoplasies in response to similar environments.
In the future the fine structure of the kidney and
pericardium of shelled Sacoglossa should be studied
in detail.
INTRODUCTION
Traditionally the Sacoglossa have been included
as a monophyletic clade within the Opisthobranchia
(Gosliner, 1981; Haszprunar, 1985a; Schmekel, 1985;
Jensen, 1996a,b, 1997c; Mikkelsen 1996, 1998).
However, inclusion of molecular data has led to
ambiguous relationships among the Euthyneura
169
KATHE R. JENSEN
Figure 1:
A, Cylindrobulla sp. drawn by K.R. Jensen. B, Ascobulla fischeri from Jensen and Wells, 1990. C, Volvatella viridis from Jensen, 2003. D, Julia
japonica redrawn from Kawaguti and Yamasu, 1962. E, Berthelinia darwini from Jensen, 1997a. F, Oxynoe azuropunctata, modified from Jensen,
1980. G, Roburnella wilsoni redrawn from Marcus, 1982. H, Lobiger souverbii redrawn from Marcus and Hughes, 1974
170
COMPARATIVE MORPHOLOGY OF THE MANTLE CAVITY ORGANS OF SHELLED SACOGLOSSA,
WITH A DISCUSSION OF RELATIONSHIPS WITH OTHER HETEROBRANCHIA
(=Opisthobranchia + Pulmonata) (Wägele et al.,
2003; Grande et al., 2004; Vonnemann et al., 2005).
The early molecular studies left the Sacoglossa
relatively unresolved between Opisthobranchia and
Pulmonata (Thollesson, 1999; Dayrat et al., 2001),
but these studies included only one or two species
of Sacoglossa. Several new studies have indicated a
closer relationship between the Sacoglossa and the
Siphonariidae, a family of limpets usually referred to
the Pulmonata (Grande et al., 2008; Klussmann-Kolb
et al., 2008; Dinapoli and Klussmann-Kolb, 2010;
Jörger et al., 2010; Dinapoli et al., 2011; Dayrat et
al., 2011).
The mantle cavity and the pallial organs have
been used to elucidate evolutionary theories for the
Gastropoda for many years (reviewed by Lindberg
and Ponder, 2001). The mantle structures of shelled
Sacoglossa are poorly studied. Most information
is from descriptions of new species or anatomical
re-description of old species. The few existing
comparative studies have been conducted from the
point of view that the Sacoglossa were firmly lodged
in the Opisthobranchia (Gonor, 1961; Morton, 1988;
Jensen, 1996b, 1997a,b).
The shelled Sacoglossa comprises the genera
Cylindrobulla, Ascobulla, Volvatella, Berthelinia,
Julia, Oxynoe, Lobiger and Roburnella (Fig. 1).
The bivalved genera Tamanovalva, Edenttellina
and Midorigai are here considered synonyms of
Berthelinia as no synapomorphic characters have been
described to justify separate genera. The inclusion of
Cylindrobulla in the Sacoglossa has been discussed
previously (Jensen, 1989, 1996a,b; Mikkelsen,
1996, 1998), and the phylogenetic relationship of
families and genera of shelled Sacoglossa remains
unclear (Händeler and Wägele, 2007; Händeler
et al., 2009; Maeda et al., 2010). Usually four
families of shelled Sacoglossa are recognized: (1)
Cylindrobullidae (Cylindrobulla), (2) Volvatellidae
(Volvatella, Ascobulla), (3) Juliidae (Julia, Berthelinia
(Tamanovalva, Edenttellina, Midorigai)), (4)
Oxynoidae (Oxynoe, Lobiger, Roburnella).
Based on morphological characters the
Volvatellidae, Julliidae and Oxynoidae form a
monophyletic suborder, Oxynoacea (Jensen, 1996a),
and Cylindrobullidae is most likely sister group to
all remaining Sacoglossa (Jensen, 1996a,b), although
some molecular studies include it in the Oxynoacea
(Händeler and Wägele, 2007; Maeda et al., 2010).
Cylindrobulla and Ascobulla (Fig. 1A, B) have almost
identical cylindrical, thin, fragile shells with elastic
periostracum and a sutural slit and keel (Jensen, 1989,
1997c; Jensen and Wells, 1990; Mikkelsen, 1998).
Volvatella (Fig. 1C) also has a thin, fragile shell with
an elastic periostracum. Posteriorly the aperture is
drawn out forming an exhalent spout. The foot is
relatively short, even in the extended state, and there
are no parapodia or external pallial lobes to support
the shell. In all of these three genera the head and
foot may be completely withdrawn into the shell, and
the shell may be contracted by an anterior adductor
muscle (Jensen, 1996a,b, 1997c).
The Juliidae are the bivalved sacoglossans. The
shell in these species has been divided into two
“valves” of which the left bears the typical spirally
coiled protoconch and the right one covers the
mantle fold. The “valves” are connected by an elastic
ligament. The animal can be completely retracted into
the shell (Baba, 1961). In Julia (Fig. 1D) the shell is
thick and the protoconch is located far towards the
posterior end. Berthelinia (Fig. 1E) has thin shells
and the protoconch is located only slightly behind
the middorsal point. Several fossil genera are known
from this family (Le Renard et al., 1996).
In the Oxynoidae the shell covers only the
visceral mass and there is a long muscular tail and
lateral muscular parapodia. The head and anterior
foot may be partly retracted into the shell, but
the tail and parapodia cannot. The aperture of the
shell is very wide. Oxynoe (Fig. 1F) has one pair
of parapodia, which can cover the shell almost
completely. Roburnella (Fig. 1G) has low parapodia,
which carry two pairs of rolled extensions; these
may be folded across the shell or extended laterally.
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KATHE R. JENSEN
Figure 2:
Cylindrobulla sp. A, dorsal view after removal of shell. B, right anterior view, C, left side view, D, ventral view, E, mantle floor after removal of
mantle fold. Arrow points to posteriormost point of aperture, i.e., where mantle edge turns forwards. F, ventral view of same, showing entrance to
upper whorls. Legend: a – anus; add – shell adductor muscle; ar – adhesive ridge; cs – cephalic shield; dci – dorsal ciliated band; dci2 – dorsal
ciliated band of penultimate whorl; dg – digestive gland; f – foot; fa – female aperture; fg – female glands; hy2 – second band of hypobranchial
gland; i – intestine; ip – infrapallial lobe; k – apical keel of shell; me – mantle edge; g – gill; he – heart; hy – hypobranchial gland; sg – spawn
groove; sh – shell; vci – ventral ciliated band.
172
Table 1: List of species and origin of material
Referencea
Species
Locality/year
Use
Cylindrobulla phuketi Jensen, 1989
Phuket, Thailand 1990
Dissection
Jensen, 1989, 1996b
Cylindrobulla sp.
Solomon Isl., 2007
Dissection
present study
Ascobulla ulla (Marcus and Marcus,
Florida, 1978
Sections
1970)
Marcus and Marcus,
1956; Jensen, 1996b;
Mikkelsen, 1996, 1998
Ascobulla fischeri (Adams and
Albany, WA, 1988
Dissection,
Angas, 1864)
Jensen and Wells, 1990;
SEM
Jensen, 1996b
Dissection
present study
Ascobulla fragilis (Jeffreys, 1856)
Mar Menor, Spain, 1993
Volvatella australis Jensen, 1997
Darwin, NT, 1993; Houtman Dissection
Jensen, 1997a,b; present
Abrolhos Islands, 1994
study
Volvatella ventricosa Jensen and
Albany, WA, 1988
SEM
Jensen and Wells, 1990
Singapore, 2006
Dissection
Jensen, 2009
Berthelinia babai (Burn, 1965)
Victoria (Australia), 1988
SEM
present study
Berthelinia darwini Jensen, 1997
Darwin, NT, 1993; Houtman Dissection
Jensen, 1997a,b; present
Abrolhos Islands, 1994;
study
Wells, 1990
Volvatella vigorouxi (Montrouzier,
1861)
Cottesloe, WA, 1996
Berthelinia rottnesti Jensen, 1993
Rottnest Isl, WA 1991
Dissection
Julia cf. zebra Kawaguti, 1981
New Caledonia, 1993
Dissection
Roburnella wilsoni (Tate, 1889)
Rottnest Isl., WA 1991, 1996 Dissection
Lobiger souverbii Fischer, 1856
Barbados, 1977
Jensen, 1993
present study
Jensen, 1993; present
study
Dissection
Marcus, 1957; present
study
Oxynoe antillarum Mørch, 1863
St. Thomas, US Virgin
Sections,
Islands, 1982; Florida, 1992
dissection
1970; present study
Oxynoe azuropunctata Jensen, 1980
Florida, 1978
Dissection
Jensen, 1980
Oxynoe viridis (Pease, 1861)
Abrolhos Islands, WA, 1994
Dissection,
Jensen and Wells, 1990;
Darwin, NT, 1993
SEM
Jensen, 1997b
Sicily, 1998
Dissection
Oxynoe olivacea Rafinesque, 1819
Marcus and Marcus,
Schmekel and Portmann,
1982; present study
a
Description or re-description of anatomy
Lobiger (Fig. 1H) has a very flat shell and two pairs of
long parapodia, which usually have scalloped edges
and a brightly colored pigmented band on the inner
surface. The parapodia are usually held erect and
with infolded margins, but if the animal is disturbed it
extends the parapodia laterally, exposing the brightly
colored bands.
In the present study mantle organs of all shelled
sacoglossan genera are examined. Taxon sampling
is considered important, and particularly those
genera for which anatomy is scantily described
have been included. Only one species of Julia,
J. japonica Kuroda and Habe, 1951, has been
studied anatomically (Yamasu, 1968), and also the
anatomy of the monospecific genus Roburnella is
insufficiently described (Jensen, 1993). The following
organs and structures have been examined: Mantle
edge, gill, osphradium, heart and pericardium,
kidney, hypobranchial gland, ciliated bands, pallial
gonoducts, intestine and anus, and shell adductor
muscle. This has been compared with literature
information on heterobranch gastropods, especially
“lower pulmonate” taxa from marine and brackish
water, and the relationship of the Sacoglossa within
the Heterobranchia is discussed.
173
KATHE R. JENSEN
Figure 3:
Volvatella australis. A, dorsal view after removal of shell. B, ventral view of same. Arrow points to mantle edge with glandular bosses. C, ventrolateral view of same. D, dorso-lateral view of same after removal of mantle fold. Legend: a – anus; add – shell adductor muscle; add2 – left side
attachment of adductor muscle; al – anterior lobes of cephalic shield; dci – dorsal ciliated band; dg – digestive gland; dl – dorsal lobes of cephalic
shield; f – foot; g – gill; he – heart; hy – hypobranchial gland; hy2 – second band of hypobranchial gland; i – intestine; ip – infrapallial lobe; me –
mantle edge; ph – posterior surface of head; vci – ventral ciliated band.
MATERIALS & METHODS
RESULTS
The species used in this study are listed in Table
1, and overview drawings of mantle structures and
general anatomy can be found in the publications listed
in the table. Most of the species have been anatomically
described by the author, and light microscopy
preparations, some stained with acetocarmine prior
to mounting, and serial sections (hematoxylin-eosin
or toluidine-blue stained), have been re-examined
and photographed with a digital camera mounted on
dissection and compound microscopes. The genera
that have not previously been examined by the author
have been dissected and also additional specimens of
previously studied species have been included. SEM
preparations were made by dehydrating in a series of
ethanol-acetone followed by critical point drying and
mounting on SEM-stubs.
General outline of mantle cavity in shelled
Sacoglossa
174
In shelled Sacoglossa the longitudinal axis of the
body whorl of the shell and visceral mass is in the
same plane as that of the head-foot, i.e., they are almost
bilaterally symmetrical. Hence the terms anterior and
posterior when describing mantle structures refer
to anterior and posterior in relation to the head-foot
longitudinal axis. Similarly, left and right refer to
positions relative to this axis regardless of the fact that
there is an involute spire in most genera.
The mantle fold in the shelled Sacoglossa is
a thin sheet of tissue, which consists mostly of
hemolymph spaces and scattered muscle strands
Figure 4:
Posterior mantle edge with glandular bosses. A, Ascobulla fischeri; arrow points to glandular bosses. B, Ascobulla fragilis; arrow points to
glandular bosses. C, Light micrograph of Volvatella australis; insert is a higher magnification of same; white arrows point to droplets secreted from
glands. D, Light micrograph of section of mantle and infrapallial edges of Ascobulla ulla. Legend: dg – digestive gland; f – foot; gb – glandular
boss; ip – infrapallial lobe (secreting callous covering inner lip of shell); me – mantle edge; sg – groove with shell gland; sh – shell; vci – ventral
ciliated band.
between two layers of epithelium (Fig. 4D). The
mantle edge is thicker and contains the shell gland
along a submarginal line (Fig. 4C). Ciliated cells
are numerous along the mantle edge, and also gland
cells occur.
In the Volvatellidae and Cylindrobulla the mantle
cavity is large, extending the full turn of the body
whorl at the level of the gill. The mantle fold
thus completely surrounds the visceral mass, which
forms the floor of the mantle cavity. Behind the gill
the ciliated bands and associated glandular bands
continue into the “upper” (involute) whorls, not
as a separate, exogyrous pallial caecum but as an
extension of the mantle cavity (Figs 2F and 3B).
Anteriorly the opening to the mantle cavity is blocked
by an anterior adhesive ridge and the right side
attachment of the adductor muscle (Figs 2B and 3A).
There is a functional incurrent aperture between the
adductor muscle and the female genital papilla (Fig.
2D). Behind this the mantle cavity is functionally
closed by the ciliated ridges running along the mantle
margin dorsally and the infrapallial lobe ventrally
(Fig. 3B). Along the mantle margin of the narrow part
of the aperture are regularly spaced epithelial bosses
along the edges of mantle as well as infrapallial lobe
(Figs 3B and 4A-C). These bosses contain glands,
which in living animals exude a transparent substance
in response to minor disturbance. Posteriorly an
excurrent aperture is formed by the apical sutural
slit. In Volvatella the posterior shell spout functions
as excurrent aperture. In juvenile specimens of
Volvatella the anterior aperture is large as in Oxynoe
(see below), but the overlapping part of the body whorl
and the visceral mass comprise an increasing part
of the shell. The infrapallial lobe contains digestive
175
KATHE R. JENSEN
Figure 5:
Juliidae. A, Berthelinia darwini, right lateral view after removal of shell. B, same (different specimen) after removal of shell and mantle fold. C, same
specimen as A, mantle fold, internal view. D, Julia cf. zebra right lateral view after removal of shell. E, same, left lateral view. F, same after removal
of mantle fold. Legend: a – anus; add – shell adductor muscle; f – foot; g – gill; he – heart; hy – hypobranchial gland; i – intestine; ip – infrapallial
lobe (=left mantle fold); pp – pharyngeal pouch; r – rhinophore; sg – spawn groove; vci – ventral ciliated band-
176
gland tubules (Fig. 4D), and in some species of
Volvatella digestive gland tubules also extend into the
mantle roof.
In the Juliidae the mantle cavity extends the full
size of the right valve (Fig. 5A, C, D). The mantle
fold is attached only along the dorsal line and at
the subcentral adductor muscle. In Julia cf. zebra
there may be a partial anterior closure formed by
the long, muscular pharyngeal pouches (Fig. 5D, F),
but no observations on living animals are available
to confirm this. In the Oxynoidae there is a large
anterior mantle cavity, which can accommodate the
retracted head (Fig. 6A-C, F). Behind this, the mantle
cavity is closed off by muscles that may be cephalic
or pharynx retractors. Between these muscles the
mantle fold is attached by an adhesive ridge to the thin
epithelium covering the retracted pharyngeal complex.
The mantle cavity opens on the right side between the
retractor muscle and the conspicuous female genital
papilla, behind which the mantle cavity of Oxynoe is
functionally closed by the base of the right parapodium.
In Roburnella two incurrent openings may be formed if
the basal parapodium is contracted, leaving an opening
between the two parapodial extensions at the level of
the gill. Posteriorly an excurrent aperture is formed by
the mantle edge, which is reflected over the posterior
part of the shell aperture. In Lobiger the posterior
margin of the mantle fold, which forms the excurrent
siphon, is displaced from the “spire” of the shell, which
is located on the left side. In Oxynoe and Lobiger the
mantle edge often has pigmented spots as found on
rhinophores, parapodial and foot margins.
Gill
The sacoglossan gill consists of a band of parallel
lamellae located in the mantle roof behind the heart
and on the surface of the kidney. In Cylindrobulla,
Ascobulla and Volvatella the gill extends a full 360°
(or more when the outer lip overlaps the reflected
inner lip). It consists of longitudinal lamellae,
completely surrounding the visceral mass of the body
whorl (Figs. 2A-D and 3A-C). More than 100 lamellae
have been counted in large specimens of Ascobulla
and Volvatella. Even juvenile specimens of Volvatella
with shell length of less than 1 mm and visible
protoconch have a fully formed gill. Almost half of
the gill lamellae are located ventrally when the animal
crawls on a horizontal surface. Unless the respiratory
current is very strong, these lamellae will most likely
collapse. During feeding (and probably also during
burrowing in Cylindrobulla and Ascobulla) the shell
is held slightly upwards, which will permit extension
of all the gill lamellae.
In the Juliidae the gill is in a vertical position due to
the lateral compression of these species. In Berthelinia
the gill extends the height of the right valve (Fig. 5A,
C), but in Julia the gill continues across the middorsal
line to the left side (Fig. 5E). In Oxynoe the gill is
located rather far towards the posterior end, probably
to make room for the pharyngeal complex when this is
retracted (Fig. 6A-B). Each gill lamella may be folded
(Mikkelsen, 1998) or smooth, and it may be longer
towards one end (Fig. 7D). The shape does not seem
to be species specific, but may be related to individual
size, larger specimens needing a larger respiratory
surface. Short lamellae are found interspersed with
long lamellae of the full gill length (Fig. 7A-B). The
epithelium of the gill lamellae is ciliated, though
the cilia do not form discrete bands; sometimes cilia
occur in tufts scattered on the surface, sometimes the
cilia appear to be evenly distributed on the surface.
Hemolymph spaces (vessels) are found in each lamella
(Fig. 8B, D). Along the anterior edge a distinct “efferent
vessel” is found. In dissections it was not possible to
see whether it connects the gill sinuses to the auricle
or the pericardium. A corresponding “afferent vessel”
runs along the posterior edge of the gill.
Osphradium
The small osphradium is located on the right side
of the mantle roof, adjacent to the attachment point
of the adductor (or retractor) muscle. It is innervated
by a small osphradial ganglion, connected to the
supraesophageal ganglion. Due to the tough texture
177
KATHE R. JENSEN
Figure 6:
Oxynoidae. A, Oxynoe viridis after removal of shell. B, Oxynoe olivacea after removal of shell. C, Oxynoe antillarum after removing shell and
mantle fold and cutting off right parapodium. D, Roburnella wilsoni after removal of shell and cutting off parapodia. E, same after removal of
mantle fold. F, Lobiger souverbii after removal of parapodia. Legend: a – anus; dci – dorsal ciliated band; dg – digestive gland; e – eye; ep –
esophageal pouch; fp – female genital papilla; g – gill; he – heart; hy – hypobranchial gland; mb – muscular bulges of oral tube; me – mantle edge;
pa – parapodium; ph – pharynx; pl – parapodial lobe (cut off); pp – pharyngeal pouch; r – rhinophore; rm – retractor muscle; si – exhalant siphon;
t – tail; vci – ventral ciliated band.
178
of the adductor muscle the mantle is often torn at this
point during dissection as well as serial sectioning.
This makes the osphradium difficult to locate. Usually
the osphradial ganglion can be identified (Fig. 9C,
D), but not the fine structure of the osphradium. In
Cylindrobulla and Volvatella the osphradium is oval
(Fig. 9A, B), in Berthelinia and Lobiger it appears to be
circular (Fig. 9C, D). The position of the osphradium
indicates that it is associated with closure of the
anterior (incurrent) mantle opening.
Heart and pericardium
The heart, composed of one auricle and one
ventricle, is located in a thin-walled pericardial sac
in front of the gill, i.e., the pericardial complex is
located in the mantle roof. The auricle is usually
triangular in outline (Fig. 10A, D) and the ventricle
may be triangular (Fig. 10A, C, D) or almost circular
(Fig. 10B). In Ascobulla and Volvatella the heart is
seen approximately in the dorsal midline of the body
(Fig. 3A) and bent at an angle relative to the gill. The
aorta passes from the ventricle into the visceral mass,
which marks the left anterior border of the mantle
cavity. Marcus and Marcus (1956) described the heart
of Ascobulla ulla (as Cylindrobulla sp.) as torted, i.e.,
with the ventricle posterior to the auricle. This has not
been seen in any of the shelled species studied here; the
auricle is always behind the ventricle. In the Oxynoidae
the heart is big and the ventricle is oriented slightly
towards the left (Figs 6B and 10D). In Berthelinia the
heart is located dorsally in the mantle fold (Fig. 5C). In
Julia it is found on the left side of the body, near the
“posterior” end of the gill (Fig. 5E). Pericardial glands,
as seen in many Acteonoidea (Rudman, 1972a,b,c),
have not been observed in any species of Sacoglossa.
Kidney
The kidney forms a thin layer of tubules running
parallel to the gill lamellae, which are attached to the
surface of the kidney (Fig. 8A, C). The tubules are
lined by highly vacuolized epithelium (Fig. 8B, D),
characteristic of gastropod kidneys. A nephrostome
or syrinx has not been observed, but in some cases
branching vessels occur in the pericardium (Fig.
10A). Marcus (1957) described a renal pore behind
the gill in Lobiger souverbii, and in Berthelinia limax
and Julia japonica the renal pore was found between
the gill lamellae towards the dorsal end (Baba, 1961;
Yamasu, 1968).
Hypobranchial gland
In all shelled sacoglossans there is a band of
white mucus secreting glands behind the gill (Figs
2A-D, 3A-C, 5A, C-D, 6A, 10C). This is considered
homologous to the hypobranchial gland of other
gastropods. In some species, e.g. Volvatella vigourouxi
the glandular cells are orange in live animals rather than
white (Jensen, 2009). In Cylindrobulla, Ascobulla and
Volvatella there is a second glandular band behind the
dorsal ciliated band (Figs 2A-C and 3A-C). In Oxynoe
the corresponding white gland forms a triangular patch
just inside the mantle margin behind the gill (Fig. 6A);
it continues as a narrow band along the afferent vessel
as in the other species. There is a second glandular
area associated with the dorsal ciliated band near
the excurrent opening (Fig. 10C); this has previously
been interpreted as the hypobranchial gland (Jensen
and Wells, 1990). In Lobiger and Roburnella the
hypobranchial gland is very thick.
Ciliated bands
This is one of the important synapomorphies of the
Euthyneura and lower Heterobranchia and the outline
of these bands have been used to develop phylogenetic
hypotheses (Haszprunar, 1985a; Mikkelsen, 1996). In
shelled Sacoglossa the ciliated bands are usually not
distinctly elevated from the surrounding epithelium,
but the cilia appear to be both longer and denser than
in the general mantle surface (Fig. 4D). The ventral
ciliated band is usually more elevated than the dorsal
one (Fig. 2E, F), and in many species the anus opens
just anterior to the ventral ciliated band (Figs 2E, 3D,
5F, 6C). In Cylindrobulla, Ascobulla and Volvatella
the ciliated bands are rather wide, about the same
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KATHE R. JENSEN
Figure 7:
SEM photos of sacoglossan gills. A, Ascobulla fischeri. B, Volvatella ventricosa. C, Berthelinia babai. D, Oxynoe viridis.
Legend: hy – hypobranchial gland; pe – pericardium; si – exhalant siphon.
width as the gill, and they are curved forwards along
the right edge of the gill in the mantle roof and along
the infrapallial lobe in the mantle floor (Fig. 2D).
In the Juliidae the ciliated bands are very narrow
and at least the one on the mantle floor (on the right
side of the body) distinctly elevated (Fig. 5F). In the
Oxynoidae the ciliated bands are indistinct. The fact
that the ciliated bands extend into the upper whorls of
the shell, all the way to but not into the protoconch,
shows that this is part of the mantle cavity rather than
a pallial caecum as seen in many Acteonoidea and
Cephalaspidea (Rudman, 1972a,b,c; Brace, 1977).
Probably it is the long dense cilia of the prominent
ciliated bands that drive the ventilation current of
the sacoglossan mantle cavity. This may be aided
180
by contraction of the shell adductor muscle where
present. In the upper whorls the ciliated bands may
have a respiratory function; hemolymph spaces occur
below the epithelium of the ventral ciliated band.
Pallial gonoducts
There are no real pallial gonoducts in the
Sacoglossa. The duct of the bursa copulatrix enters
the female genital papilla at the mantle floor on the
right anterior side. In Berthelinia the female mucus
gland may form a bulge in the mantle floor (right
side of body), but it remains embedded in the visceral
mass. In the Oxynoidae the female genital papilla is
very big (Fig. 6A,C-E), whereas there is no distinct
papilla at the female genital opening of Cylindrobulla
(Fig. 2D). The vas deferens is embedded in the body
wall medially to the female genital opening and
thus not visible inside the mantle cavity. There is a
separate penial opening in the cephalic region.
Intestine and anus
The intestine of shelled sacoglossans is short,
ascending through the digestive gland from the stomach
to the mantle floor. In Cylindrobulla, Ascobulla and
Volvatella the intestine is seen as a white line on the
mantle floor on the surface of the digestive gland; the
anus is in front of the ventral ciliated band (Figs 2E
and 3D). In Berthelinia the intestine appears on the
surface of the mantle floor behind the bulge formed
by the mucus gland of the female reproductive system
and in front the ciliated band (Fig. 5B). In Julia only
a short segment of the intestine is visible dorsally
on the surface of the digestive gland in front of the
ciliated band (Fig. 5F). In Roburnella the intestine runs
diagonally on the surface of the digestive gland on the
right side. The anus opens towards the ventral side (Fig.
6E). In Oxynoe (Fig. 6C) and Lobiger the anus is more
dorsal on the surface of the digestive gland. Pigmented
anal glands, as seen in several lower heterobranchs
(Haszprunar, 1985a; Ponder, 1991), have not been
observed in shelled Sacoglossa.
Shell adductor muscles
A shell adductor muscle forming a scar on the
shell valves was first described for the Juliidae when
these were still thought to be bivalves. This muscle
has been intensively studied in the Japanese species
Berthelinia (=Tamanovalva) limax (Kawaguti
and Yamasu, 1960a,b). It develops soon after
metamorphosis as a diagonal muscle connecting
the incipient right “valve” and the left side of
the teleoconch. In the adult Juliidae the adductor
muscle is usually distinctly visible by its darker or
denser colour (Fig. 5A-F). It is surrounded by a thin
epithelium and therefore easily separated from the
visceral mass during dissection. On the other hand
it is very difficult to cut loose from the mantle fold
without ripping the latter.
A shell adductor muscle has also been identified in
Cylindrobulla (Jensen, 1989; Mikkelsen, 1998; present
study), Ascobulla (Marcus and Marcus, 1956; Jensen
and Wells, 1990; Mikkelsen, 1998), and Volvatella
(Baba, 1966; Jensen and Wells, 1990; Jensen, 1997a,b;
present study). Here it is less conspicuous, running
diagonally from the anterior right corner of the mantle
fold (and shell) (Figs 2A and 3A) to the inner lip of the
shell on the ventral side (Fig. 3C). In the Oxynoidae
the aperture is wide and there is no use for an adductor
muscle. The muscles attaching to the shell are the
retractors of the head and/or the pharyngeal complex.
DISCUSSION
Examination of the mantle cavity and its associated
structures in 18 species of shelled Sacoglossa from
all 8 genera has yielded several conclusions: (1)
The inclusion of the genus Cylindrobulla in the
Sacoglossa is confirmed. Most of the characters
shared with other shelled sacoglossans have been
considered plesiomorphic, but in this study the
character of regularly spaced glandular bosses along
the posterior mantle and infrapallial lobe edges
has been found in Cylindrobulla, Ascobulla and
Volvatella. This character has not been described in
other opisthobranchs or heterobranchs, and if this
is considered a synapomorphy, then Cylindrobulla
may be included in the suborder Oxynoacea. Also,
the long lamellate gill attached throughout its length
to the surface of the kidney and the diagonal shell
adductor muscle are synapomorphies shared by the
three genera. However, the suprageneric affiliations
of Cylindrobulla cannot be determined on the basis of
only shell and mantle characters.
(2) The gill consisting of parallel folds forming
a band across the mantle roof differs from that of
all other heterobranchs by being located on the
surface of the kidney. This has been described many
times before in individual species descriptions, e.g.,
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KATHE R. JENSEN
Figure 8:
Light micrographs of sacoglossan gill and kidney. A, Ascobulla ulla stained with hematoxylin-eosin. B, same at higher magnification. C, Oxynoe
antillarum stained with toluidine-blue. D, same at higher magnification. Legend: dg – digestive gland; g – gill lamellae; k – kidney tubule with
vacuolized epithelium; mc – mantle cavity; pa - parapodium
Ascobulla ulla (as Cylindrobulla sp.) (Marcus and
Marcus, 1956), Berthelinia (=Tamanovalva) limax
(Baba, 1961), Oxynoe viridis (as Lophocercus viridis)
(Eliot, 1906), Lobiger serradifalci (Mazzarelli, 1892)
and L. souverbii (Marcus, 1957), but apparently
nobody has attached any phylogenetic importance to
it. Gill structure and attachment differ widely among
the Heterobranchia (Table 2), and it seems likely that
homoplasies are involved.
182
(3) Shell adductor muscles are found in
Cylindrobulla, Ascobulla, Volvatella and the bivalved
Juliidae. The osphradium is located where this muscle
attaches to the mantle fold, indicating that the muscle
is activated when the osphradium is stimulated. In the
Oxynoidae retractor muscles, cephalic or pharyngeal,
serve as attachment of the body and mantle fold to
the shell on the left side, and on the right side are
associated with the osphradium, thus probably having
Figure 9:
Position of osphradium or osphradial ganglion in shelled sacoglossans. A, Cylindrobulla phuketi; arrow points to presumed osphradium. B,
Volvatella australis; arrow points to osphradium. C, Berthelinia darwini; arrow points to osphradial ganglion. D, Lobiger souverbii; arrow points to
osphradial ganglion. Legend: add – shell adductor muscle; g – gill; rm – retractor muscle.
the function of retracting the head, which closes
off the incurrent opening, when adverse factors are
detected by the osphradium.
(4) In the bivalved genus Julia the mantle cavity
extends across the middorsal line of the shell. This
is interpreted here as more ancestral than the shorter
mantle cavity of Berthelinia, covering only the right
side of the body.
(5) The sacoglossan mantle cavity is closed off
anteriorly by muscles and an adhesive ridge, and
opens on the right side of the body. This indicates
a 90º (partial) detorsion. However, the heart is
oriented at an angle which is usually less than 45º
from the longitudinal axis of the body, indicating
almost complete detorsion. Also, the heart is located
approximately in the middorsal line, as in the nonshelled Sacoglossa. The almost completely detorted
heart as well as its position differ from the situation in
183
KATHE R. JENSEN
Figure 10:
Heart of shelled sacoglossans. A, Volvatella australis. B, Ascobulla fragilis. C, Oxynoe azuropunctata. D, Lobiger souverbii. Legend:
au – auricle; dci – dorsal ciliated band (apparently on glandular tissue); g – gill; hy – hypobranchial gland;
pe – pericardium; ve – ventricle.
Acteonidae (Fretter and Graham, 1954; Brace, 1977)
and also from lower pulmonates (Table 2; Brace,
1983).
Comparison with other Heterobranchia
The reorganization of Euthyneura (=
Opisthobranchia + Pulmonata) was initiated with the
resurrection and re-definition of the Heterobranchia
184
(Haszprunar, 1985a). Since then the basal clades
of Opisthobranchia, Pulmonata and “lower
Heterobranchia” have been moved around in almost
every analysis that has been published (Grande et al.,
2008; Klussmann-Kolb et al., 2008; Malaquias et al.,
2009; Dinapoli and Klussmann-Kolb, 2010; Jörger et
al., 2010; Dinapoli et al., 2011; Dayrat et al., 2011).
For comparison with shelled Sacoglossa several of
these “problematic” taxa were selected (Table 2).
Omalogyridae, Cornirostridae and Orbitestellidae
are classical “lower Heterobranchia”, i.e. small
species with a dextral shell (Haszprunar, 1988;
Ponder, 1990a,b, 1991). The Glacidorbidae and
Amphiboloidea also have dextrally coiled shells, but
have variously been included in the Pulmonata or
“lower Heterobranchia” (Ponder, 1986; Golding et
al., 2007). The Pyramidelloidea has been transferred
from “Prosobranchia” to “Opisthobranchia”
based on morphological characters (Fretter and
Graham, 1949), and later to “lower Heterobranchia”
(Haszprunar, 1985a). Pyramidelloidea typically
have small heterostrophic shells, but limpet-like
forms exist (Ponder, 1987). The Acteonoidea were
traditionally included in the Opisthobranchia
(Fretter & Graham, 1954), but were transferred to an
informal group, “Architectibranchia” (Haszprunar,
1985a; Grande et al., 2004). Morphologically the
Acteonoidea are similar to many Cephalaspidea
having typical “bubble-shells” (Mikkelsen, 1996).
The genus Akera is included in the Anaspidea
in morphological as well as molecular studies
(Morton, 1972), but was previously considered a
typical cephalaspidean (Brace, 1977). Its shell has
several similarities to that of Cylindrobulla and
Ascobulla, e.g., sutural slit and keel (Jensen, 1996b).
The Siphonariidae are limpet-like gastropods,
usually included in basommatophoran Pulmonata
(Yonge, 1952; Marcus and Marcus, 1960), although
anatomical affinities to Opisthobranchia have
been pointed out (Köhler, 1893). Till recently the
Heterobranchia were assumed to have affiliations
with taenioglossate Caenogastropoda (Haszprunar,
1985a; Ponder, 1991). However, the inclusion of the
family Hyalogyrinidae with rhipidoglossate radula
and apparently a true ctenidium in the Heterobranchia
due to their heterostrophic shells and presence
of ciliated bands in the mantle cavity (Warén
and Bouchet, 2009) has added further confusion
to the origin of Heterobranchia. Hyalogyrinidae
have typical dextral shells with a large umbilicus.
In shelled Sacoglossa the body whorl completely
overgrows the “upper” (inner) whorls, so that in
adult animals the protoconch is completely hidden.
Interpretation of the evolution of gastropod
mantle cavity and the pallial organs has changed
through time (Lindberg and Ponder, 2001). In
many “lower Heterobranchia” the gill is absent
or reduced (Table 2). In the species which have
a gill it is interpreted as a secondary one, due to
absence of skeletal rod and arrangement of cilia
(Ponder and Lindberg, 1997). True ctenidia are
connected to vessels originating from the kidney
(Ponder and Lindberg, 1997). The sacoglossan gill
lamellae also contain vessels that surround the renal
tubules, whereas in “Architectibranchia” (sensu
Haszprunar, 1985a) as well as most Cephalaspidea
the kidney is wedged in between the gill and the
pericardium, and vessels from the gill run across
the kidney (Fretter and Graham, 1954; Rudman,
1972a,b,c; Brace, 1977). Ponder and Lindberg
(1997) claim that the kidney is located to the right
of the pericardium in heterobranchs as well as
caenogastropods. In the shelled Sacoglossa the
kidney is located behind the pericardium, and blood
flow is most likely from mantle vessels through the
kidney to the gill lamellae and from the gill to the
auricle. A direct connection from the kidney to
the pericardium may also be possible considering
the close relationship between these organs in
shell-less Plakobranchoidea. Unfortunately the fine
structure of the kidney of shelled Sacoglossa
has not been described, but the ultrastructure of
the kidney and excretory system was studied in
two non-shelled species (Fahrner and Haszprunar,
2001). They found podocytes in the epicardial
wall of the auricle of Bosellia mimetica. This is
considered plesiomorphic in the Mollusca.
The sacoglossan gill has been interpreted
as a variation of the typical opisthobranch
plicatidium (Mikkelsen, 1996). However, a band
of simple, sparsely ciliated folds is difficult to
homologize with the complex structures found in
“Architectibranchia”, or Cephalaspidea (Fretter and
Graham, 1954; Rudman, 1972a,b,c; Brace, 1977).
The gill structure is superficially similar to the
gills found in siphonariids, i.e., it consists of a band
185
186
Omalogyridae
Absent
Absent
In mantle roof;
posterior
Anteriorly
from anus (or
on left side)
Associated
with ciliated
bands
Obliquely
across
posterior
mantle wall
Deep in
mantle cavity
on right side
Fretter, 1948;
Haszprunar,
1988
Character
Gill
Osphradium
Kidney
Ciliated bands
Hypobranchial
gland
Heart
Anus
References
Ponder, 1990b
Behind
kidney; left of
gill; in
posterior
mantle roof
To the right of
gill base
Absent;
pigmented
strip present
Possibly
replaced by
pallial tentacle
Behind gill;
anterior to
heart
Small;
anterior, left
Cornirostridae
Triangular,
bipectinate;
mostly free
Ponder, 1990a
In posterior
part of mantle
cavity
Mantle gland
present behind
osphradium;
pigmented
Behind kidney
in posterior
mantle roof
Absent;
ciliated lobe
present on
right side
In mantle roof;
anterior to
heart
Present; left
Orbitestellidae
Absent
Ponder, 1986;
Right
posterior
Behind
kidney, at
posterior
mantle wall
Absent
Absent or
indistinct, but
ciliated mantle
fold present
In mantle roof;
large
Absent
Glacidorbidae
Absent
Hubendick, 1945;
Golding et al.,
2007
Anterior right side
Anterior to
kidney;
pigmented; or
absent
On extreme left
side of mantle
cavity
Full length of
mantle cavity, or
only exhalent
Simple; at
anterior right side
of mantle roof
In mantle roof
Amphibolidae
Absent
Fretter and
Graham, 1949;
Haszprunar,
1985b; Ponder,
1987
In left posterior
end of mantle
cavity
Behind kidney; in
visceral mass or
posterior of
mantle roof
Pigmented mantle
organ
Not reaching
posterior margin
of mantle cavity;
on right side
Simple; left of
dorsal ciliated
band
In mantle roof;
anterior to anus
Pyramidellidae
Absent or present
Deep in mantle
cavity; left of
ventral ciliated
band
Fretter and Graham,
1954; Rudman,
1972a,b,c; Brace,
1977
Posteriorly or
transversely on left
side
Associated with
ciliary bands, or
absent
From mantle edge
(anteriorly or
exhalent siphon)
into pallial caecum
Large; left side of
mantle roof
Acteonoidea
Plicate; partly
attached (to roof
and floor of mantle
cavity)
Small, anterior; on
left side
Posterior to
ventral ciliated
band, at exhalent
siphon
Morton, 1972;
Brace, 1977
On left anterior
side of mantle
cavity
Curving
backwards on
right side into
long, attached
pallial caecum
Absent
In mantle roof;
anterior to gill
Akera
Plicate; partly
attached by
membrane to
kidney and floor
Small, anterior;
on right side
Table 2: Comparison of mantle structures of shelled Sacoglossa and 9 other heterobranch taxa
Köhler, 1893;
Hubendick, 1945;
Yonge, 1952;
Marcus and
Marcus, 1960; de
Villiers and
Hodgson, 1987
On right side of
mantle floor; at
exhalent opening
On left anterior
side; transversely
oriented
Siphonariidae
U-shaped band of
parallel lamellae;
attached; behind
kidney
Close to right
anterior end of
shell muscle
Large; 2 parts
(one in mantle
roof, one in
mantle floor)
Dorsal and ventral
bands transversely
across mantle
cavity posterior to
gill
Absent
Deep in mantle floor
in front of ventral
ciliated band; facing
posteriorly
Mazzarelli, 1892;
Marcus and Marcus,
1956; Baba, 1961,
1966; Gonor, 1961;
Jensen, 1989, 1993,
1996a,b, 1997a,b,
2009; Jensen and
Wells, 1990; present
study
Middorsal, in front of
gill (and kidney);
almost completely
detorted
Narrow bands along
dorsal ciliated band
Dorsal and ventral
bands from right
mantle opening to
innermost whorl
In mantle roof; band
overlying gill
Sacoglossa
Band of parallel
lamellae encircling
body whorl; attached
to surface of kidney
Small; right, anterior;
next to adductor
KATHE R. JENSEN
of parallel lamellae, each lamella consisting of a
fold of epithelium with scattered ciliated cells and
surrounding a hemocoelic space with transverse
trabeculae (Villiers and Hodgson, 1987). However,
in the Siphonariidae the gill is located behind (and
above) the kidney, and the heart is turned about
90º from the longitudinal axis of the body (Yonge,
1952; Villier and Hodgson, 1987). Also, growth of
gill lamellae in Siphonaria may be different from
that of shelled Sacoglossa. In Siphonaria capensis
the largest gill lamella are found towards the center
of the U-shaped gill (Villier and Hodgson, 1987),
indicating that new lamellae are added towards the
ends. In shelled Sacoglossa short gill lamellae occur
in between long ones, and only towards the inner
and outer ends are lamellae generally shorter. This
indicates that addition of new lamellae during growth
occurs between two existing lamellae. This growth
pattern has also been suggested for Siphonaria
alternata (Yonge, 1952). Architectonicidae, another
“lower heterobranch” family, also has a lamellate
gill, but here the gill lamellae are formed by
folding of the epithelium of the hypobranchial
gland (Haszprunar, 1988). Thus the gill lamellae
are solid, composed of two cell layers. In the
limpet-like pyramidelloid Amathina tricarinata the
gill is also composed of parallel lamellae attached
to the mantle roof. However, the gill is located in
front of the kidney, and the pericardium and heart
are located behind this (Ponder, 1987). In some
“Architectibranchia”, e.g. Acteon tornatilis the gill
is attached by a membrane to the edge of the kidney,
but the gill structure of these species is much more
complex (Brace, 1977; Jensen, 1996b), and in the
Siphonariidae the kidney is wedged in between the
gill and pericardium, and furthermore it is divided
into a dorsal and ventral lobe (Yonge, 1952; Villier
and Hodgson, 1987).
Opposing ciliated bands in mantle roof and floor
are considered a synapomorphy of all Heterobranchia
(Haszprunar, 1985a; Ponder and Lindberg, 1997;
Warén and Bouchet, 2009), though Ponder (1991)
noted that ciliated bands were probably independently
derived in several heterobranch groups. Apparently
they are absent in several small groups (Table 2).
In shelled Sacoglossa the ciliated bands extend into
the upper whorls, forming a small cavity on the
surface of the visceral mass. This was interpreted
as an “attached” pallial caecum (Jensen, 1996a,b),
but probably should be considered a true part of the
mantle cavity. The pallial caecum of Akera, although
attached to the visceral mass, only extends over one
whorl (360°) (Morton, 1972). In Siphonaria dorsal
and ventral ciliated bands are located behind the gill,
following the outline of the posterior gill margin
(Villier and Hodgson, 1987), and a small pallial
caecum has been described in S. hispida (Marcus and
Marcus, 1960).
The osphradium of heterobranch gastropods is
less complex in structure than that of caenogastropods
(Haszprunar, 1985b). In Architectonicids and
pyramidellids the osphradium is located in the left
side of the mantle cavity. In most cephalaspids the
osphradium is located to the right of the attachment
membrane of the gill (Edlinger, 1980; Haszprunar,
1985b). In Acteon it is located in front of the gill
base (Edlinger, 1980), whereas it is at the extreme
anterior left side of the mantle cavity in some other
acteonids (Rudman, 1972a). An osphradium has not
been described in Hydatina, Bullina and Micromelo
(Rudman, 1972b,c), and it seems to be absent in most
of the heterobranch groups that do not have a gill
(Table 2). In the shelled Sacoglossa the osphradium
is inconspicuous in preserved specimens, but may
be identified more easily in live animals (Gonor,
1961). Its fine structure has not been examined,
but it is associated with the adductor or retractor
muscle located at the anterior right opening of the
mantle cavity. A similar position of the osphradium
has been observed in several species of Siphonaria
(Hubendick, 1945; Yonge, 1952; Marcus and Marcus,
1960) and also in Amphiboloidea (Table 2) and the
eupulmonate Chilinidae (Brace, 1983). In Akera
the osphradium is also at the right anterior corner
of the mantle cavity, but to the right of the anterior
adductor muscle (Brace, 1977).
187
KATHE R. JENSEN
The hypobranchial gland is generally thought to
be homologous throughout the Gastropoda (Fretter
and Graham, 1954; Ponder and Lindberg, 1997).
However, several other glands may occur in the
mantle cavity of the Heterobranchia. These include
the opaline and purple glands of Anaspidea (Morton,
1972; Dayrat and Tillier, 2002), repugnatorial glands
of several Acteonoidea and Cephalaspidea (Fretter
and Graham, 1954; Rudman, 1972a,b,c; Wägele and
Klussmann-Kolb, 2005), and the “pigmented mantle
organ” (PMO) of several “lower heterobranchs”
(Ponder, 1987; Table 2). In the shelled Sacoglossa
glands are located along the mantle margin, but more
densely between the gill and dorsal ciliated band.
According to Fretter and Graham (1954) the ciliated
bands are formed in the hypobranchial area, and
the glands accompanying the bands are considered
homologous with the hypobranchial gland.
The present study has found a number of
morphological similarities between the shelled
Sacoglossa and the Siphonariidae. However, these
are either plesiomorphic (ciliated bands, lamellate
and attached gill with different location) or possibly
homoplasies (position of osphradium). The shell
muscles of the siphonariids are probably not
homologous to the shell adductor muscle or cephalic
retractor muscle of the Sacoglossa, and therefore the
association of the osphradium with muscles at mantle
opening are related to function rather than being
homologous. Most siphonariids are intertidal and
most sacoglossans also live in shallow water. Hence
the morphological similarities may be interpreted as
adaptations to a similar environment. Some molecular
studies have the Sacoglossa and Siphonarioidea as
sister groups and the combined clade as sister group
to the remaining Pulmonata plus Glacidorboidea,
Amphiboloidea, Pyramidelloidea and Acochlidia
(Klussmann-Kolb et al., 2008; Jörger et al., 2010).
Others have a paraphyletic grade of Sacoglossa,
Siphonarioidea and the above groups, with either
the Sacoglossa being basal to the remaining groups
(Dayrat et al., 2011) or the Siphonarioidea (Dinapoli
et al., 2011). Dinapoli and Klussmann-Kolb (2010)
188
have an unresolved trichotomy. What seems clear
is that the Sacoglossa are not closely related to
any of the traditional opisthobranch groups. The
sacoglossan gill is probably not homologous with
the plicatidium, and the almost completely detorted
heart shows that they are probably not closely
related to “lower Heterobranchia”. However, it is
not possible to infer a phylogenetic relationship with
the Siphonarioidea or with any pulmonate group,
including Pyramidelloidea and Acochlidia. If further
molecular studies should continue to support an
affiliation of the Sacoglossa and the Siphonariidae,
other organ systems of both groups need to be
analyzed by comparative morphology.
ACKNOWLEDGEMENTS
The majority of the material used in the present
study has been collected during several international
workshops in Australia. The organizers of these
workshops are thanked for providing the permits
and facilities and Carlsberg Foundation for funding
my participation, and for funding microscopes and
digital camera equipment. Collecting in Ghizo,
Solomon Islands was funded by a grant from
Villum Kann Rasmussen Foundation to prof. R.M.
Kristensen of the Zoological Museum (SNM) in
Copenhagen, and was part of the Danish Galathea
3 Expedition 2006-2007. Specimens from Florida
were collected as part of my Ph.D. study at Florida
Institute of Technology, Melbourne, Florida. Dr.
J. Just, formerly at the Zoological Museum in
Copenhagen, now in Townsville, Australia, collected
the specimens of Lobiger souverbii in Barbados,
Dr. P. Gianguzza, University of Palermo collected
Oxynoe olivacea in Sicily, Dr. J. Templado, Museo
National de Ciencias Naturales in Madrid provided
the specimens of Ascobulla fragilis, and Julia cf.
zebra was obtained from the Muséum national
d’Histoire naturelle in Paris thanks to Dr. P. Bouchet.
Finally I wish to thank Dr. J. Troncoso and his team
for organizing the 3rd International Opisthobranch
Workshop, providing the opportunity to present the
results of the present study.
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FROM “TREE-THINKING” TO “CYCLE-THINKING”:
ONTOGENETIC SYSTEMATICS OF NUDIBRANCH MOLLUSCS
ALEXANDER V. MARTYNOV(1)
Key words: ontogeny, evolution, phylogenetics, ontogenetic systematics, synthesis, ontogenetic cycles, heterochrony, paedomorphosis,
evolutionary models, molluscs, opisthobranchia, nudibranchia, doridacea
ABSTRACT
During the last decade traditional morphological
paradigm of evolutionary biology has been
challenged. Molecular systematics and morphologybased phylogenetics were considered as “advanced”
fields compared to the “old-fashioned” traditional
systematics. At the same time, an enormous body of
the practical and theoretical methods of “traditional”
biology was considered usually in a minimal degree.
It is here demonstrated that the current evolutionary
paradigm in the “phylogenetic era” lacks a theory of
how organisms change their shape. The links between
evolution, ontogeny, systematics and phylogenetics
are prima facie obvious, but similarly greatly
underestimated currently, though the field of “evodevo” is continuously growing. As a synthesis (or
more exactly, re-synthesis) of the still in considerable
(1) Zoological Museum, Moscow State University, Bolshaya
Nikitskaya str. 6, Moscow 125009 Russia.
E-mail: [email protected]
degree independently developing major biological
fields, i.e. ontogeny, evolution and taxonomy, the new
conception of ontogenetic systematics is therefore
suggested; the practical usefulness of the new concept
is illustrated by some examples from nudibranch
molluscs. Such re-formulation of apparently wellknown and obvious biological knowledge implies
also a great challenge for current phylogenetics and
systematics: an understanding of the necessity to
consider not only evolutionary “lines” and “branches”
of the “Tree of Life”, but also its cycle nature, since
ontogenetic cycles are indispensable and active parts
of the process of evolution.
FROM SYSTEMATICS TO EVOLUTION AND
VICE VERSA: THE CURRENT PARADIGM
After collapse of the classical biological
science following by two world wars, traditional
systematics underwent rapid evolution leading to
dramatic changes in this field. Major agenda of
the unprecedented challenge for the systematics
become the “search for objectivity”. Following this
way several schools pretending on an objective
systematics emerged consequently. Phenetics refused
193
ALEXANDER V. MARTYNOV
classical systematic hierarchy in favour of “direct”
measurement of a dimension between characters
(Sokal & Sneath, 1963). Initial enthusiasms of
phenetists soon was declined and replaced by the
next paradigm – phylogenetic systematics (Henning,
1966). Phylogenetic systematics became the most
prolific and successful branch of the “objectivitydriven” taxonomy, first of all because it was actually
a stricter reformulation of the classical heritage
of Darwin’s (1859) and Haeckel’s (1866) texts.
I.e. phylogenetic systematics, exactly in Darwinian
sense, converted traditional taxonomic hierarchy
into a consequence of the evolutionary events. Heated
debates around theoretical foundations of taxonomy
featured 1970S and 1980S and caused formation of
the modern paradigm (see e.g. Wiley, 1981; Ridley,
1986; Pesenko, 1989; Wägele, 2005; and many
others). Very shortly outlined, this paradigm implies
tree-thinking instead of taxon-thinking.
In other words, there are no more “statical” taxa
of classical systematic hierarchy, but instead any
(monophyletic) taxon should be regarded as a part of
an endless “Tree of Life”. To produce this, traditional
hierarchy should be “ripped” and separate characters
afterward need to be “extracted” and reanalyzed
under various methods (e.g. Wiley et al., 1991). Then,
a new, apparently objective hierarchy of characters
(and taxa) is expected to appear. The breakthrough
in computer technologies almost not leaved a space
for critics of such an approach and “new, easy,
and objective” phylogenetics celebrated their victory
over all 1990S and earlier 2000S. Both modern and
classical zoological periodicals then rapidly showed
thousands of trees of strict dichotomic forms.
The major target of phylogenetic systematics –
reconstruction of a definite “Tree of Life” apparently
was so close, but real results soon demonstrated a
completely different picture. A principal theme of most
of the phylogenetic studies instead became “absence of
resolution of phylogenetic trees” (see almost any paper
that contains morphological phylogenetic analyses,
e.g. Dayrat, Gosliner, 2005). Major advantages of the
194
phylogenetic systematics – reconstructing/showing the
historical sequence of the morphological apomorphies
was soon almost completely disregarded by some
authors (e.g. Scotland et al., 2003). Though few authors
attempted to advocate importance of morphology
itself as dataset for reconstructing phylogeny
(e.g. Wiens, 2004), and though a so-called “bioontological” approach has been developed (see e.g.
Ramírez et al., 2007; Vogt, 2009), modern systematics
soon was transformed into “phylogenies without
synapomorphies” (see Mooi & Gill, 2010).
Even as promisingly claimed often recently, that
a reasonable study should include both morphology
and molecules (see e.g. major topics for the
planning in October 2011 a large-scale international
conference Deep Metazoan Phylogeny 2011 at
Ludwig-Maximilians-Universität München), this
does not prevent for transforming the until quite
recently extremely fashionable morphology-based
phylogenetic systematics into an auxiliary discipline,
in favour of the molecule-based “fourth great school
of systematics” – the “It-Doesn’t-Matter-Very-Much
school” (see Felsenstein, 2004, p. 145). Finally, most
of the recent researchers will eagerly answer “yes”
on a question whether or not “A new and general
theory of molecular systematics emerged” (Edwards,
2009) (see e.g. any content of any journal where the
word “evolution” is mentioned; few examples could
be cited – e.g. Dunn et al., 2008; Lartillot, Philippe,
2008). Substantial revision of traditional systems (e.g.
Halanych, 2004), apparently caused by the new field
emergence, forces even traditional taxonomists and
evolutionary morphologists, especially (still) wellestablished in Russia, for uncritical acceptance of the
results of molecular phylogenetics and claims for a
“revolution in systematics” (see e.g. Shatalkin, 2005).
The general current enthusiasm about molecular
phylogenetics is so overwhelming (even despite on
numerous problematic issues – see e.g. Philippe et
al., 2011a), that any opposite or just more balanced
views could be easily interpreted as an “old-fashion”
adherence of an author with old ideas. Nevertheless,
one of such attempts will be performed here.
FROM “TREE-THINKING” TO “CYCLE-THINKING”: ONTOGENETIC SYSTEMATICS OF NUDIBRANCH MOLLUSCS
Considering the above outlined few key-points of
the “modern” systematics development it is possible
to conclude that several generations of “objective”
approaches have substituted each other during
the last 50 years. The current one is molecular
phylogenetics, and it actually includes elements of
all previously “eaten by each other” approaches:
analysis of numerous separate characters apart from
any hierarchy concept of phenetics and the cladistic
approach of Hennigian phylogenetic systematics
that, in contrast, is based on the at least idealistic
assumption of homology of characters.
Many shortcomings of the traditional systematics
leave of course a possibility for some kind of
“misuse” of its methods, leading e.g. to so called
splitting and lumping, arbitrary- and authority-driven
classificatory schemes, a potential possibility for
almost “endless” split a higher taxon into subtaxa,
etc., and partially provoked the XX-century race
for “objective systematics”. But is the molecular
phylogenetics exactly the long-expected substitution
for the “fabulously arbitrary” classical systematics?
As it was admitted by molecular phylogenetists
themselves, “Phylogenetics is still a difficult and
controversial field, because no foolproof method is
yet available to avoid systematic errors” (Lartillot
& Philippe, 2008, p. 1469). Special bioinformatics
literature is full of debates of the usefulness of
the different mathematical models of the nucleotide
substitutions and alignment algorithms. All
the enormously branched field of the molecular
systematics is constructed on the probabilistic
principles that are not “hided”, but instead, widely
advertised (see Nei, Kumar, 2000; Felsenstein, 2004;
Lukashov, 2009; and many others).
However, even the phylogenetic theorists
and bioinformatics specialists are in doubt while
attempting to distinguish “truth” and “statistics” in the
molecular phylogenetics (see e.g. Wägele et al., 2009;
Kumar, 2010; Philippe et al., 2011a). The exponential
growth of the new publications in this field already
has led to the hardly avoidable contradictions. E.g.,
the famous Ecdysozoa vs. Coelomata controversy:
currently phylogenetists claim that the new data clearly
in favour of the former (e.g. Holton, Pisani, 2010), but
numerous previous contradicting studies most likely
suggested that is not a final conclusion. In turn, newest
nudibranch phylogenies based, for the first time, on a
substantial taxon sampling, resulted, however, mostly
in a conclusion, that “our results do not resolve all
the relationships within the Cladobranchia” (see Pola
& Gosliner, 2010, p. 931). In the meanwhile, on two
main problems of the molecular phylogenetics —
incompleteness and absence of a definite resolution
have been pointed soon after the new field became
a mainstream (see, e.g. Jenner, 2000). It is quite
clear that obtaining of the large molecular data sets
and developing of the sophisticated molecular tools
is of much benefit for the independent checking of
the evolutionary-morphological hypotheses. However,
there are still so scarce data in favour of the true
objectivity of such approach. Some remarkable
examples of controversies, e.g. on the phylogenetic
position of animals with extremely simple morphology,
like Acoela, where molecular phylogenetic methods
prima facie unquestionably superior over traditional
approaches, revealed however, that the range of
discussions even in the newest publications (i.e. basal
vs. derived simplified position of acoelomorph –
Mwinyi et al., 2010 vs. Philippe et al., 2011b) is
comparable with the past debates in the evolutionary
morphology field (e.g. Ivanov, Mamkaev, 1973). And
after 15 years of active developing of sophisticated
programs for molecular phylogeny reconstructions,
professional taxonomists recommend “use biology, not
algorithms to make homology decisions” (see Mooi &
Gill, 2010, p. 26).
Thus, as a result of more than 40 years of
theoretical discussions and about 20 years of practical
applications, the field of phylogenetic systematics,
while performing their great quest for objectivity,
have provided us with: 1. New arbitrariness, 2. Novel
preconceptions, 3. Absence of the strict resolution, 4.
Doubts in monophyly of every taxa. That was therefore
almost entirely missed in the apparently exhaustive
195
Figure 1:
New model of the dorid evolution. Ancestral notaspid and dorid ontogenetic cycles (external features). Elaboration (prolongation) of the notaspid
ontogeny led to appearing of the complicated cryptobranch ontogenetic cycle, whereas it further heterochronic modifications caused appearing of
the variously juvenilized phanerobranch dorid families up to strongly paedomorphic Corambidae group. The prognostic features of this model imply
presence of the cryptobranch postlarval stages in the newly discovered Onchimira cavifera, despite that real ontogeny of this taxon is completely
unknown yet. Drawing by T.A. Korshunova based on A.V. Martynov originals.
theoretical discussions, which are included perhaps
thousands of papers and hundreds of monographs,
and that have led to the current situation? The answer
is very simple, quite disappointing, and somewhat
contradicting even with the first lines of the present
paper. This almost entirely forgotten field is the
traditional systematics. This, quite humble and clearly
endangered (even the recent great rising of “Zootaxa”
could not completely prevent traditional systematics
from the label of “old-fashioned”) in the modern time,
scientific tribe of professional taxonomists almost
300 years already has performed their really great
task – finding a way how to describe independently
from our consciousness existing patterns of the
organisms in a most consistent manner.
196
Despite of the methods of traditional systematics
have slightly changed since the Linnean time, they still
successfully allow to describe these independentlyexisted phenomena – taxa of the systematic hierarchy.
Very important for the aims of the present paper
is the fact that traditional systematics still acted
independently from any phylogenetic study itself
(does not matter, morphological or molecular), despite
on repeated claims of the tree-priority over the taxa
themselves. In a most paradoxical way, the traditional
taxonomy in the second part of XX century became
a real “keeper” of true objectivity in the study of
organism diversity. No traditional systematist will
ever place a dandelion into a phylum Arthropoda and
to the family of the harvest mites (Trombiculidae),
but instead into a division of the flowering plants
(Angiospermae or Magnoliophyta) and to the family
Asteracea. In a similar way, it is hardly expected, that
a bivalve molluscs will be considered by traditional
systematist as a polychaet, or that a nudibranch
mollusk will be named as a cephalaspid.
Thus, prima facie absolutely combinative and
“typological” method of the taxa formation actually
have led to discovery of the independent from a
particular observer natural phenomena — really
existing groups of organisms, united by a set of unique
characters. In any country, a student, professional
expert or amateur unequivocally and independently
will confirm existence of such groups, e.g. bivalve
molluscs, polychaet worms or mammals. The
independent multiple confirmations is a base for any
scientific knowledge and in this respect, paradoxically,
traditional systematics comparable with exact science.
In other words, traditional systematists in course of
almost 300-years of the taxonomy development have
learned perfectly how to structurally attributed any,
previously unknown specimen to a known taxon of the
systematic hierarchy.
And if a taxonomist will find a mollusk
with crawling sole, radula and also, with a spiral
protoconch, but with a two-valved shell, he will
definitely consider this unusual taxon as an aberrant
member of the class Gastropoda, not as an aberrant
member of the class Bivalvia. Moreover, several
fine, complex “enough” morphological features
of the two-valved snails, including radula and
reproductive system unambiguously point to the
subclass Opisthobranchia, and even more exactly, to
the order Sacoglossa. Understanding that Julia and
Berthellinia are the members of the class Gastropoda
and subclass Opisthobranchia at the level of soft body
morphology (Kawaguti & Baba, 1959) then helps
to paleontologists recognize their initial mistake
in assessing of the fossil shells of the two-valved
sacoglossans to the class Bivalvia. Is it an ideal of a
scientific knowledge? Professional taxonomists are
of course well aware about numerous “dangers” of
the traditional systematics. Nevertheless, a system
generated of the knowledge of traditional systematists,
even methodologically almost lacking any notions on
the evolutionary process, comes much more close
to a yet not existing “ideal” of the biologicallybased theory of the historical transformations of the
organisms, than any modern taxa and ranking-free
statistics-aided study of nucleotide substitutions in the
molecular phylogenetic field. This is because they are
able to distinguish and define (name) any organisms
structurally and use the hierarchical principle.
There are no doubts though, that structural
approach itself has many restrictions – that were a
driving force for the past and present challenges for
the theory of systematics. Traditional systematics
offers mighty methods for exactly recognizing
organismal patterns, but almost do not consider
causes of emerging of such patterns, i.e. evolution.
Therefore, finding, for instance, some aberrant taxa
within a well-established taxonomical group (e.g.
opisthobranch order Doridacea), which are, similar
to the apparently ancestral (for dorids) Notaspidea
by gill patterns (i.e. dorid family Corambidae),
traditional systematics may relatively easily be
misled in assessing their relationship. However it
will be too simple and premature labeled the classical
systematics as a non-evolutionary and “typological”
(e.g. Mayr, 1963; Hennig, 1966). Because, as it is
sometimes eluding from the current thinking, one
of the major evidence for the evolution itself became
exactly existence of the systematical hierarchy
(Darwin, 1859). In another word, the properties of
the traditional systematics allow for relatively easy
converting it into a sequence of the evolutionary
event (Haeckel, 1866). And though it sounded so
sensational in the 1970-80S, Hennigian phylogenetic
systematics was actually a quite obvious and much
postponed almost direct implication of the Darwin’s
and Haeckel’s key texts.
Thus, we have an obvious, but still not solved
in a most consistent way, contradiction: traditional
systematics very well works with the recognition
197
of unique taxa, but almost does not include an
evolutionary approach. Whereas phylogenetic
systematics (including molecular), instead, built
on strict evolutionary principles, but considerably
disregard the fact that any living thing exists not only
as a “ line” or “branch”, but forms also particular,
separate organisms, quite “closed” systems called
species, which are able to exist millions of years just
slightly changing. Moreover, all organization of the
living organisms demonstrates a hardly disputable
conservatism: most of the metazoan phyla have been
traced already in Cambrian, that means therefore, that
not only the morphological, but also physiological,
molecular and ontogenetic basis of any modern
animals have not changed significantly in course of
the last half of the billion years!
Is it possible to suggest some set of theoretical
and practical instruments that may challenge current
paradigm that can be shortly named as “treethinking”? Because the rapidly growing field of
“phylogeny reconstruction” is almost not interested
in the fundamentals, on which any evolutionary study
is based, and the molecular phylogenetics is not an
exception. Is it therefore possible, that suggestions
how to link the “immobile” traditional systematics
and idea of the historical transformation of the taxa
(i.e. evolution) in most consistent and natural way,
from “point of view” of the real biological processes,
and not the statistical probability calculation, already
have emerged in the history of biology, but a working
method based on such ideas was not formed? And
some modern reformulation, of apparently already
quite well established ideas is therefore required?
ONTOGENETIC CYCLE — THE UNIT OF
SYSTEMATICS AND EVOLUTION
Perhaps among one of such apparently obvious
and self-evident ideas, that is simultaneously
underestimated by both traditional systematics
and modern phylogenetics, is the principle that
any organism can be understood only as a part of
a particular ontogenetic (or life) cycle. This was
198
already quite evident for the Ancient Egyptians
(see Hennig, 1966), and became one of the most
basic elements of the continuously growing modern
field of the evolutionary developmental biology
(commonly known as “evo-devo”). Few essentially
similar quotations may be included that “Morphology
considers organism not only in the adult condition,
but also in all preceding stages of their development”
by classic of the comparative and evolutionary
morphology, Carl Gegenbaur (1859, S. 1) and “Any
organism does not possess an ontogenetic cycle,
but instead part of it” by modern biologist John
Bonner (1965). In this respect, special emphasis on
the relation between ontogeny and evolution was put
in Russian science by comparative and evolutionary
morphologist Vladimir Beklemishev (1925, 1969),
who featured his understanding of any organism
not as a static structure like morphologists and
systematists, but instead as the morphoprocess, e.g.
continuous flow of various processes, and first of all,
the ontogenetic cycle itself (see e.g. Korotkova, 1979;
Ivanova-Kazas, 1995 and many others). Beklemishev
specially highlighted that exactly the life cycle of any
species is the unit of the comparative morphology
(see Beklemishev, 1969, introduction). Benedictus
Danser (1950, p. 142), Dutch plant taxonomist, quite
unequivocally formulated this principle for the field
of systematics: “The life-cycle with its multiformity
is the smallest unit of classification”.
In this respect, major deficiency of the current
phylogenetics (in any from) in “low resolution” of taxa
relationship appears not due of the not enough degree
of the advancements of algorithms and software, but
in fundamentally incorrect basic concept regarding
the most important biologically-based properties of
the organisms – the ontogenetic cycle. As it was
already mentioned above, modern phylogenetics it is
a somewhat hybrid between evolution-free phenetics
and, strictly evolutionary phylogenetic systematics.
Both books of Sokal & Sneath (1963) and Hennig
(1966) thus became an indispensable basis of the
modern phylogenetics. And in both monographs
properties of the ontogenetic cycles were either
not considered at all (Sokal & Sneath, 1963) or
specifically interpreted (Hennig, 1966). Already on
the first pages of Hennig’s fundamental publication,
the entire ontogenetic cycle was actually “ripped” into
independent stages of the “semaphoronts” (Hennig,
1966), “character bearers”, and the major problems to
assign different developmental stages to one species,
without direct observations, was highlighted. Such
methodological approach was important for Hennig
in order to find stricter bases of his theory. However,
widely cited and too superficially and incorrectly
interpreted, most likely, they opened a way for further
consideration not only taxonomy, but also ontogenetic
cycle itself as a predominantly combinative fields,
lacking their own strict patterns. The Sokal & Sneath
“Numerical Taxonomy” (1963), apparently built
their theoretical apparatus on a completely different
ground than Hennig, and just not considered almost
any biological properties (including ontogenetic
cycle) at all, but instead formulated an “operational
taxonomical unit” (OTU), as super-formal ground for
the taxa construction. However, these both so different
books have produced in total very similar effect,
which can be most well described as “founder effect”:
the key importance of the ontogenetic cycle was
almost vanished from entire field of the phylogenetics
and systematics. And a modern important review on
the methods of the phylogeny reconstruction easily
avoided even one mention (!) of the fundamental
biological term – ontogeny (see Felsenstein, 2004),
thus perfectly recapitulates one of their own most
important ancestor – the Sokal & Sneath’s book
“Numerical Taxonomy”.
The importance of the ontogeny for the
understanding of evolution has not disappeared from
the scientific publications completely, but rather
transformed into a special field. The modern founder
of the field is of course famous German biologist
Ernst Haeckel and his immediate predecessor, Fritz
Müller. The latter suggested basic principles of the
ontogenetic and evolutionary interactions (Müller,
1865) prior to the Haeckel’s first monumental
monograph “Generelle Morphologie” (Haeckel,
1866). Nevertheless, we still should thank Haeckel not
only for one of the most consequential defending of
the evolutionary theory, but also for the formulation
of the terms ontogeny and phylogeny, facts which
are most likely well remembered only by a handful
of modern molecular phylogenetists. It is quite hard
to understand now, but in the second part of the XIX
and first half of the XX centuries ontogeny was an
important and actually integral part of many of the
systematic and evolutionary studies. The famous
Haeckel’s agenda “ontogeny recapitulates phylogeny”
has received controversial acceptance, and there were
many repeated attempts to challenge the biogenetic
law (e.g. Sedgwick, 1909), but a comprehensive theory
of the interaction of the ontogeny and evolution for the
first time was suggested by the Russian morphologist
and embryologist Alexei Severtsov (also spelled
as Sewertzoff) (1912, 1931). Ten years prior to the
well-known paper of Garstang (1922, p. 81, claimed
that “no one has presented [until now] a complete
theoretical scheme capable of replacing Haeckel’s as
an explanation of the relations between ontogeny and
phylogeny”), Severtsov exactly and unequivocally
suggested such a theory that finally allowed to
reformulate the biogenetic law: not phylogeny is the
source for ontogeny, but instead ontogeny creates
evolution (Severtsov, 1912; Garstang, 1922; Levit et
al., 2004, p. 349–353).
What is the important difference in such
re-formulation? The key-importance for the entire
evolutionary field is due to the very clear understanding
that not some obscure historical processes along the
endless branches of the Tree of Life are responsible
for the evolution, but instead, the routine “miracle”
of each new ontogeny formation and their slight or
pronounced modifications solely feature the evolution
itself. This new understanding of Haeckel’s law
opened new horizons in evolutionary studies and have
lead to formation of a particular field of the studies
of the interaction between ontogeny in evolution.
For many decades, this field was developed quite
independently in Russia (USSR) and in USA. In both
countries independent sets of theoretical instruments
199
Figure 2:
Comparision of the morphological patterns of opisthobranchs molluscs of the group Notaspidea, ancestral to all dorids (gill, lag and anal opening,
an are ventro-lateral, rhinophores, rh — without pockets, their bases united) with adult (gills, dg and anal opening, an are dorso-terminal,
rhinophores, rh have pockets and diverged) and postlarval (gills absent, anal opening ventro-terminal, rhinophores without pockets and united)
morphology of the cryptobranch dorids. A, B, C — Berthellina citrina (Ruppell et Leuckart, 1828) (Notaspidea), adult specimen 23 mm length; D —
Сadlina laevis (L., 1767) (Doridacea), adult specimen 25 mm length; E — C. laevis, postlarval stage ca. 500 μm length; F — C. laevis, preceding
early postlarval stage ca. 400 μm length. Scale bars: B, C — 1 mm; E, F — 100 μm (on lower inset, E — 30 μm).
Photos: O.V. Savinkin (A), T.A. Korshunova (D). SEM micrographs (B–F): A.V. Martynov. Further abbreviations: fn — frontal part of notum;
lag — lateral gill; no — notum; ppl — primary posterior notal lobes.
200
for the description of the phylogenetic effects of the
ontogenetic shifts have been established. In Russia it
became the phylembriogenesis concept of Severtsov
(1912; 1934) and his successors (e.g., Schmalhausen,
1938, 1969 and many others). In USA, instead
dominated attempts of re-formulating concepts of
Haeckel’s initially auxiliary term heterochrony
(De Beer, 1930; Gould, 1977; Alberch et al., 1979;
McNamara, 1997 and many others). Both schools have
used basically the same principle, i.e. the “ontogeny
defines evolution”, but make different accents and
use somewhat different methodological tools. For
instance, in the Russian theory of phylembryogenesis,
researchers persisted in using a quite “rigid” scheme,
describing the alteration of the ontogeny leads to
the evolutionary effects only at three levels: earlier
ontogenetic changes (archallaxis), middle ontogenetic
stages (deviation) and, finally, most recent additions
to a given ontogeny (anaboly). The main idea referred
to the wholeness of organisms and their ontogenetic
cycles (e.g. Schmalhausen, 1938).
On the contrary, the approach of dissociability
(Needham, 1933) featured the Gould (1977) version of
the theory of interaction of the ontogeny and evolution
and allowed to consider any organism as rather
mosaic where different parts can develop relatively
separate from each other. The dissociability concept
also allowed to construct the much more flexible
theory of heterochronic shifts of ontogeny, either
regressive (e.g. pedomorphosis) or “progressive”
(=peramorphosis) (see e.g. McNamara, 1986, 1997).
An almost one century gap between genetic and
phylogenetic approaches in biology (when Wilgelm
Roux has proclaimed his “developmental mechanics”
instead of the Haeckel’s biogenetic law) was filled
only in 1980S, when the apparently completely new
field currently known under name of “evo-devo” has
emerged (see e.g. Raff & Kaufmann, 1983; Hall, 1992,
1999, 2003; Gilbert et al., 1996; Minelli, 2003; Carroll,
2008; and many others) as a re-union of the ontogeny
and evolution. In reality, “evo-devo” should be rather
considered as a modern re-formulation of the Haeckel
biogenetic law and Severtsov’s phylembriogenesis
theory with genetic addition. The rise of “evo-devo”
was mostly coincided with the declining of the previous
ontogenetic-evolutionary concepts in both, Severtsov’s
and Gould’s version. However, seeking for a new widescope biological theory and pretending to describe
ontogenetic mechanisms (i.e. organisms’ shape
transformation), evolutionary developmental biology
almost “forgot” about true indispensable “data base”,
almost three hundred years have accumulating the
information about the non-random organism diversity
patterns – traditional systematics, that deals not with
some “theoretical” but instead with most really practical
organism shape patterns. But the most responsible field
for such “ontogenetic oblivion” is of course modern
phylogenetics, as a discpline that claimed repeatedly to
be the strict substitution of the traditional systematics.
In the 1970-80S phylogenetically-orientated theorists
virtually re-discovered the biogenetic law theme (see
Fink, 1982; Kluge, 1985; De Queiroz, 1985; Mishler,
1988; Weston, 1988; Bryant, 1991; and others), but
finally mostly concluded ontogenetic studies are
just of auxiliary importance for the phylogenetic
inference, except for few examples, which not became
a mainstream (e.g. Nelson, 1978). Even few relatively
recent attempts to refresh interactions between
phylogenetics and ontogeny have met unexpected
difficulties and such studies are still far from being
widely accepted (e.g. Jaecks & Carlson, 2001; Wiens
et al., 2005; etc.), though importance of the ontogenetic
approach is not completely vanished from the most
recent phylogenetic publications (e.g. Struck, 2007;
Box et al., 2008; Smirthwaite et al., 2009; Ji et al.,
2009).
ONTOGENETIC SYSTEMATICS
Thus, until recently both branches of the biogenetic
law developing have not led to the appearing of a
general theory of the organism shape changing. The
apparently promising synthesis, “evo-devo” might
have become such a result of the post-Haeckelian
re-thinking of the ontogeny and evolution interactions
that could have integrated major branches of biology.
201
However, “evo-devo” remains largely a discipline
applying modern technology on studying the ontogeny
of organisms. In favour of such view quite clearly
points the most recently suggested term “phylo-evodevo” (see Minelli, 2009), which was suggested as an
important novelty in one of the leading evolutionary
journal. However, since ontogeny already implies
evolution and, moreover, “evo-devo” exactly means
“evolutionary development biology”, this additional
emphasizing on “phylo-” also makes no sense because
phylogeny itself means modifications of the ontogeny
in the historical scale. In other words, this fact of
interacting ontogeny and evolution that is known
since Severtsov in 1912 is now eluding from the
enormous recent “evo-devo” field, and the principle
that “ontogeny builds evolution” continues to be
re-discovered in modern times.
Thus, despite on almost 150 years of the evident
scientific history of the interactions of ontogenetic
and evolutionary studies, thousands of publications
and hundreds of various terms (most of them are
perfectly dead now), an important synthesis and a
term connected with is still missing in this field.
I.e., despite of the very complicated history and
promising modern researches outlined above,
current evolutionary developmental biology, classical
systematics (the science, which maximally possesses
the information on the diversity and hierarchical
patterns of the morphological characters of the
organisms) and phylogenetics have all developed
mostly separate from each other. Their importance
for each other is self-evident but still greatly
underestimated in modern biology (e.g. there are no
any mentioning of the systematics on the schemes
explaining “evo-devo” synthesis – see e.g. Love,
Raff, 2003; Olsson et al., 2010). Therefore, their new
synthesis (“re-synthesis”) might become an important
source for further understanding of the historical
succession of the organisms’ shape changing, i.e.
evolution in its original sense.
A new term that features and highlights
such re-synthesis has been suggested recently as
202
ontogenetic systematics (Martynov, 2010). Despite
of the apparent easiness of creation of this term and
deep sense, uniting both ontogeny and evolution, as
far as I know, there was only one single previous
attempt to use it (see Albert et. al., 1998). However,
regardless of using identical words, the latter
publication understood under the term ontogenetic
systematics not systematics itself, but instead,
somewhat paradoxically, a molecular pathways that
can lead to formation of a structure during the
ontogeny. The term ontogenetic systematics was
suggested independently in the mentioned author’s
publications. However, these two both apparently
very different meanings of the term ontogenetic
systematics point to this highly desirable, but yet
very far from completeness general theory of the
organisms’ shape transformation, of course implies
understand of the way how the DNA information
became the macromorphological characters. And it
is a widespread modern illusion that such apparently
grandiose task the “evo-devo” field can performed
alone. Instead, an approximation to such task has
already been made, during almost 300 years, while
the traditional systematics was in searching for a
system how in a most unequivocal way to describe
organisms’ diversity. By-products of such searching
became discovery of a real and not imaginable
and methodologically very useful taxa hierarchy,
and then, as a direct consequence of the latter, the
discovery of the evolutionary process itself.
Most generally, ontogenetic systematics may be
regarded as a starting point for constructing a general
theory of the evolution of ontogenies, which largely
proceeded as the evolution of a limited set of basic
ontogenetic cycles of metazoans that originated as
early as in the Precambrian or Early Cambrian
and correspond to different phyla in the classic
systematics. Such re-formulation of apparently wellknown and obvious biological knowledge implies
also a great challenge for the current phylogenetics
and systematics: an understanding of necessity of
the consideration not only evolutionary “lines” and
“branches” of the “Tree of Life”, but also a cycle,
since the ontogenetic cycle is an indispensable and
active part of the process of evolution. I.e., it implies a
gradual shifting from current merely “tree-thinking”
to what could be named as the “cycle-thinking”.
At the same time, such shift does not implies
consideration of evolution as a strictly cyclic process,
the view that we also should thank to the Jena scientist,
Ernst Haeckel. He suggested the phases of “epacme”
(primary diversification), “acme” (“flourishing”) and
“paracme” (declining) (see Haeckel, 1866, Bd. 2, S.
320–322), that apparently every taxon “has passed” in
course of the historical development. The Haeckel’s
“thee-phases” evolution was then recapitulated in
many of the second part of XIX and earlier XX
centuries considerations; most notable became
Otto Schindewolf’s (1936, 1950) “typogenesis”,
“typostasis” and “typolysis”. However, it is quite
obvious, that despite of many taxa have been already
completely extinct, most of the basic, for instance
Metazoa structural patterns, i.e. phyla, originated
yet in the earlier Cambrian, and still exist in the
modern biosphere. It is prevented from such simplistic
representation (though, of course apparently “natural”
in analogy with the ontogeny itself) of the taxa
history in the three-phase model, but do not refused
the possibility to consider the evolution as result
of the various ontogenetic shifts (e.g., by the well
established process of heterochrony). What is very
important in such consideration is the possibility
to predict similar, either regressive (paedomorphic)
or progressive (additive) ontogenetic shifts within
various descendant taxa of the same ancestral taxon,
thus quite easily explaining the phenomenon of
parallel evolution, especially in relatively closely
related taxa. All modern phylogenetics is full of claims
for the paraphyly cases, but few modern researches
understand that mostly responsible for such pattern
are exactly the indisputable cyclic properties of the
ontogeny itself. Returning to the entire evolutionary
field, considering ontogenetic cycles as a major and
not just auxiliary principle thus much more increases
the reliability of both morphological and molecular
phylogenetics. The ontogenetic cycle thus should
become a true and not only a theoretical unit of
systematics and phylogenetics.
Such problematic issues are perfectly highlighted
by the very practical taxonomy and phylogenetics
in one of the major nudibranch groups — dorids
(Doridacea or Anthobranchia), when some aberrant
features of the dorid nudibranch family Corambidae,
such ventral anus and gills have been considered as
archaic (basal), and therefore the entire group have
been placed into the beginning of the nudibranch
classification (e.g. Odhner in Franc, 1968), and, what
is more notable, persisted even in recent reviews
(e.g. Rudman, 1998). However, as it was already
evidently shown, also by careful cladistic analysis of
the morphological characters (Martynov & Schrödl,
in press), corambids are “just” secondary regressive
descendants of the common dorid ontogenetic cycle,
originated due to the progenesis (see Martynov, 1994b;
Martynov et al., 2011; Martynov, Schrödl, in press).
The consideration of the entire ontogenetic cycle thus
helped to correctly recognize the homologies of gills
and gill cavities and thus contributed to a character set
with better signal for cladistic study. Few non-trivial
phylogenetic studies have already come to essentially
similar conclusions, most importantly, including the
molecular data (see Wiens et al., 2005). It can be
only guessed how many thousands or hundred of
thousands particular taxa incorrect evaluation and
phylogeny reconstructions will be revealed exactly
due to forgetting of the ontogenetic cycle properties.
Some important (but of course not absolutely
exhaustive), both theoretical and practical principles
of the ontogenetic systematics are listed below:
1. The ontogeny defines evolution, and not vice
versa. Therefore, — ontogeny is basis for the
phylogeny.
2. Therefore, the unit of the evolution, systematics
and phylogenetics — is the ontogenetic cycle and
not just a “clade”.
3. The primary classificatory procedure is not
connected directly with the historical or individual
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Figure 3:
Heterogeneity in construction of the rhinophoral and oral apparatus in nudibranch molluscs (Nudibranchia) and in their ancestral group —
opisthobranch molluscs Notaspidea (=Pleurobranchoidea). A — Berthellina citrina (Notaspidea: Pleurobranchidae), adult specimen 23 mm length;
B — Cadlina laevis (Doridacea), postlarval specimen ca. 400 μm length; C — Cadlina laevis, adult specimen 15 mm length; D — postlarval
specimen Cadlina laevis ca 500 μm length; E — Pleurobranchaea brocki Bergh, 1897 (Notaspidea: Pleurobranchaeidae), adult specimen;
F — Tritonia antarctica Martens et Pfeffer, 1886 (Nudibranchia), adult specimen. Scale bars: A, C, E — 1 mm; B, D — 30 μm; F — 300 μm.
SEM micrographs: A.V. Martynov. Abbreviations: fn — frontal part of notum; ov — oral veil; rc — rninophoral cavity; rh — rhinophores; rp —
rhinophoral pocket; rs — larval suture of the rinophoral pockets closing.
succession of the origin of the classification’s
objects. A systematist attributed any just
discovered new specimen on the basis of sets of
unique characters, evidently homologous within
any given stable (well-established) taxonomic
group. With only help of the classificatory scheme,
any yet unknown specimen could unambiguously
204
always incorporated (attributed) into already
known higher taxa (species to genus, genus to
family, etc. etc.) on the basis of the sets of unique
characters. Such principle could be also named as
a main principle of the systematics.
4. The evolutionary succession of the organisms’
shape transformation — it is the succession of the
formation and “disruption” of various ontogenetic
cycles. From the spawn mass of a Littorina we
expected to see a Littorina juvenile or larva
emerging, not a nudibranch veliger or a crustacean
nauplius. However, the exact shape of the newly
formed molluscs or crustacean (e.g. fine details
of shell or legs proportions) is hardly predictable.
Thus ontogeny combines great conservatism with
possibility to some shifts, which thus leave a place
for evolution. Considerable, noticeable shifts of
any ontogenetic cycles are e.g. paedomorphic
(then juvenile features persist on the adult
stages; same for progressive (“peramorphic”)
shifts; then new stages are added into a given
ontogeny). When the initial ancestral shape
is greatly distorted, then this could be named
as “disruption” of an ontogenetic cycle. This
succession of the ontogeneses in the historical
perspective (evolution) thus, forms own theory,
significantly independent from the procedure of
the attributing, describing above.
5. The biologically-based unifying theory of the
historical transformations of the organisms
should in a less contradicting way integrate
information obtained from these both main
systematic procedures: a) attributing of the yet
unclassified specimens according to the degree
of the correspondence to the already known
unique sets of the characters (taxa) and b) theory
of the historical transformations of these sets of
characters (phylogeny in a strict sense). Such
general theory which is included both listed
components is therefore suggested to term as
ontogenetic systematics.
6. Ontogeny — it is the only existing real keeper of the
memory of the preceding historical transformations.
I.e. ontogeny — it is the only single available
process allowing to link these two key-components
of ontogenetic systematics (history–independent
taxa attribution and the theory of phylogeny itself)
in a maximally objective, biologically-, and not
statistically-based way.
7. The succession of the characters allows to discover
various traces of the ancestral ontogeny (a limited
memory of the heredity system), in even greatly
modified secondarily ontogenetic cycles (e.g. a
modified nauplius larva in the rhizocephalous
crustacea allows to infer that they still belong to
the in other features completely different group
Cirripedia). I.e. there is a possibility to infer
the phylogenetic events by the real, biologicallybased processes. The succession of the characters
also implies their “trivial”, “systematic” homology
in any reasonable narrow-defined group (e.g.
rhinophores and gills within dorid group are clearly
homologous, but their exact degree of homology
to other opisthobranch group is less defined),
and also a “deep” homology between prima facie
very different structure between far related taxa.
The unequivocal homological correspondences
manifested at the morphological level may have
very complicated both molecular and ontogenetic
“recording methods” in the heredity system (see e.g.
Shubin et al., 1997, 2009). This not yet discovered
“DNA to morphology” transition mechanisms do
not prevent us from assessing these unique sets as
real characteristics of taxa.
8. The ontogenetic memory is maximally identical
between closely related species and maximally
imprecise between the very distantly related
ones. These facts allow considering traditional
evolution-free systematics within real, instead of
only “hypothetic” historical dimension. This also
implies that is senseless to search for a “succession
of all ancestors” in a given ontogeny, that is often
used as an evidence for a complete “failure” of
the biogenetic law. Such succession can be really
found, but on a restricted phylogenetic distance,
between particular taxa. Thus, only converse of the
systematic hierarchical principle into sequence of
the ontogenetic transformations, from particular
taxa to particular taxa, it is possible to construct a
general theory of systematics, i.e. general theory
of the organism shape transformations. These
statements also imply several very important
further issues: a) Recapitulations are really
existing and are mighty instruments of the
phylogeny inference, but should be used only on
205
a restricted phylogenetic distance; b) Any wellestablished taxon of traditional systematics is
an approximation to the model of the ancestral
ontogenetic cycle — i.e. such if its ancestral
species had been really existed some time ago,
and had particular, functional, and not some
formal and abstract, properties; c) Therefore,
the in the modern evolutionary and phylogenetic
theory almost completely abandoned term
“transitional taxon” or “missed link” is of great
importance and should be restored and given full
consideration as a valid and not auxiliary, “bad”
term, i.e. a heritage of old, “imprecise” and
“arbitrary” systematics.
9. There are firm evidences that some sets of
characters (that can be called as morphogenetic
networks), for instance, some “dependent”
characters of one ontogenetic cycle (e.g. juvenile
features) may became “dominating” characters
(e.g., adult, definitive), and vice versa. This
indicates that evolution does not equal freely
varying characters along the endless “branches”
of the “phylogenetic tree”, but instead, rather
within quite limited frames of particular entire
ontogenetic cycles, most basic of the have
originated already in the earlier Cambrian and
then became named by traditional systematics as
the metazoan phyla.
10. The consideration of the evolution restricted by the
particular “technological” properties of particular
ontogenetic cycles lead to the possibility of
considering the diagnosis of any well-established
traditional systematic group (taxa) higher than
species level as a minimally contradicting model
of the ancestral ontogenetic cycle, that imply
that all subtaxa included in this group should be
therefore products of the modifications of this
ancestral ontogenetic cycles.
11. Historical transformations of the ontogenetic
cycles (evolution) might perform in a regressive
way (for instance, paedomorphosis), a reduction
development of a given character (set) compared
to the ancestral condition, and in a progressive
way compared to the ancestral ontogeny. Both
206
these processes are widespread among living
organisms. Any species thus is a combination of
regressive and progressive features. Many groups
also clearly demonstrate domination of the larval
features, thus show the paedomorphosis in narrow
sense.
12. A resulting model of the phylogenetic
transformations of the ontogenetic cycles may
include the hierarchical order of the sequence
of the taxa appearing, with indications of the
major succession of the morphological structures
(key phylogenetic characters; it is a method to
distinguish a cycle within a line), graphic model
of the morphological transformations, and also a
tree-like scheme.
In a short conclusion, the “cycle-thinking”
vs. “tree-thinking” lead to another important
implication: we should not concentrate so much on
the merging of any descendant taxon with ancestral
ones, as often done by current phylogenetics, but
instead on separations of “new cycles” from “old
lines”. It is possible by detecting of the sets of the
newly emerged morphogenetic networks as keyfeatures of every new taxa, never existed in the
previous one. Restricted recapitulations on limited
phylogenetic distances became instead some
obscure theoretical considerations, but a practical
system of “reference points”, unambiguously
indicate real, and not hypothetically constructed
direction of the evolution. Thus, the ranking system
of the traditional systematics does not lose their
importance: it has a crucial role indicating the
succession of the modifications of the ontogenetic
cycles with help of the recapitulatory reference
points, but not as a continual line, but as succession
of sets of particular functional organizations,
including particular properties of a given
ontogenetic cycle. For instance, there are not any
crustaceans with veliger larvae and there are not
any molluscs with the nauplius larvae.
The usefulness of the consideration of any
well-established, “narrow-enough” in definition
by the morphological characters and apparently
monophyletic in phylogenetic terms, taxon as model
of a particular ancestral ontogenetic cycle (imagined,
thus as a really existed ancestral species, and not just
a formal node of a tree) will be demonstrated on the
example of the three taxa that are closely related
from the point of view of traditional systematics
(e.g. Thiele, 1931), morphological cladistics (e.g.
Wägele & Willan, 2001) or molecular phylogenetic
study (e.g. Jörger et al., 2010), i.e. groups of
“higher” opisthobranchs, notaspids (s.str.) and
nudibranchs that were considered earlier within
the “supertaxa” Acoela or Nudipleura. Based on
sets of unique structural characters, we recognize
three potential ancestral ontogenetic cycles within
this group, and thus further define them as order
Notaspidea s.str (=Pleurobranchoidea), order
Doridacea (=Anthobranchia) and Nudibranchia s.str.
(=Cladobranchia) and then will shortly outline some
basic properties and evolutionary potential of these
defined ontogenetic cycles in order to conclude
whether they rather represent a natural, monophyletic
unit or not. This is an initial example and an
experiment in an almost completely new field of the
biologically-based ontogenetic systematics and can
not be completely free from flaws. Further analysis
in greater details and elaboration are necessary:
Model of the ancestral ontogenetic cycle of the order
Notaspidea s.str. (=Pleurobranchoidea) (Fig. 1)
Systematic diagnosis: Notum present; Thin
internal shell under the notum or absent; Rhinophores
are well defined, enrolled and united together with
oral veil into a common structure; Mantle cavity
absent in all species; Single true gill is always on the
right lateral side under the notum; Anal opening on
the right side behind the gill and under the notum;
Genital opening in front of the gill; Jaws comprising
from numerous separate elements, always present;
Radula possess numerous uniform hook-shaped
radular rows; Central tooth absent; Digestive gland
is entire, not branched; CNS with fused cerebral
and pleural ganglia; Reproductive system is diaulic
in most species and triaulic in two species of the
genus Bathyberthella. Vas deferens is fully closed.
Copulative apparatus near female genital opening on
the left side in front of the gill.
Including families (alphabetic order):
Pleurobranchidae and Pleurobranchaeidae.
Key newly emerged morphogenetic networks
(key phylogenetic characters): Notum; Rhinophoraloral veil common apparatus; Gill apparatus and anus
free of mantle cavity on the body wall;
Model of key-transformations: Mantle
transforms into the notum (progressive); Gills
attached directly to the body wall (regressive);
Posterior corners of the cephalic shield are bending
forward and form thus enrolled rhinophores, enlarged
anterior part of the cephalic shield became oral veil
(progressive);
Phylogenetically important succession of the
key-characters: Rhinophores remain fused with
the oral veil, the feature strongly points to the
cephalic shield of Cephalaspidea s.l. Lateral gill and
lateral anus position strongly point to Cephalaspidea
s.l. Non-cephalic copulative organ weakly points to
Acteonidae.
Recapitulations: Spiral external shell of the
juvenile stages points to the basal opisthobranchs like
Cephalaspidea s.lato (including Acteonidae).
Ancestral group (strong or weak inference):
Weak inference for Acteonidae-like group ancestry
(non-head copulative apparatus).
Monophyletic status: Yes.
General model of the ancestral ontogenetic
cycle: Pelagic larva with spiral shell > benthic juvenile
with notum enclosed the shell, formation of free
enrolled rhinophores connected with each other and
with oral veil > benthic adult with internal plate-like
shell, entire notum both anteriorly and posteriorly,
enrolled rhinophores connected with oral veil, lateroventral gill and anus partially covered by notum.
Model of further ingroup evolution (major
features): Shortening of the life of pelagic larva
towards to the direct development; Shell reducing
towards complete absence; Notum reducing (not
complete); Gill reducing (not complete);
207
The Tree and the Cycle: Interaction
Adult
apomorphic
character
Juvenile plesiomorphic
character
Descendant taxon
Deletion
Adult apomorphy
character
Juvenile plesiomorphy
Ancestral taxon
Adult plesiomorphic
character
Figure 4:
General scheme illustrated interactions between evolutionary trees and ontogenetic cycles. Phylogenetic consequences of the characters
transformations in ontogenetic context: juvenile plesiomorphic character (red) capable to transform into adult apomorphic character (orange) many
times independently in different lines underlined by the same ancestral ontogenetic cycle.
Model of the ancestral ontogenetic cycle of the
order Doridacea (=Anthobranchia) (Figs 1, 5)
Systematic diagnosis: Notum present or reduced;
Internal shell always absent; Rhinophores are well
defined, solid, completely separate from oral veil and
enclosed by anterior notal margins; Oral veil small,
placed under anterior notum (if it not reduced); Mantle
cavity absent in all species; Single true gill is circularly
bent in a secondary cavity medially on the dorsal
side of notum or gill cavity absent; Few species have
ventral gills or gills are completely reduced; Genital
openings lateral; Jaws comprising from the numerous
separate elements, or monolith, often absent; Radula
possess numerous basically hook-shaped radular rows
208
differentiated and reduced in different degree; Central
tooth present or absent; Digestive gland is entire, not
branched; CNS with fused or separated cerebral and
pleural ganglia; Reproductive system is triaulic in
most species, except for some (but not all) species of
the genus Bathydoris. Vas deferens is fully closed.
Copulative apparatus near female genital opening on
the left side of the body.
Actinocyclidae, Aegiridae, Akiodorididae, Aldisidae,
Anculidae, Bathydorididae, Chromodorididae,
Dendrodorididae, Discodorididae, Dorididae,
Goniodorididae, Gymnodorididae, Hexabranchidae,
Mandeliidae,
Onchidorididae,
Phyllidiidae,
Polyceridae, Vayssiereidae.
(key phylogenetic characters): Formation of
separate rhinophores in closed rhinophoral pockets;
Solid rhinophores; Formation of a highly specialized
and complicated dorsal gill apparatus and gill cavity.
Model of key-transformations: Internal shell
completely disappeared (regressive); Separation of
the fused rhinophores into the separate pockets by
the lateral shifting and anterior notal lobes including
formation of the rhinophoral pockets (progressive);
Formation of the solid rhinophores and their complete
separation from oral veil (progressive); Single gill
and anus transit from latero-ventral to dorso-terminal
position with simultaneous formation of the closed
gill cavity (progressive).
Phylogenetically
important
succession
of the key-characters: Circumanal gills remain
associated with the anus and nephroproct strongly
point to Notaspidea s.str. and Cephalaspidea s.l.
Well defined (though solid) rhinophores point to
Notaspidea s.str. Triaulic reproductive system points
to the pleurobranchid notaspidean of the genus
Bathyberthella.
Recapitulations: Spiral shell of the juvenile stages
points to basal opisthobranchs like Cephalaspidea
s.lato (including Acteonidae) and Notaspidea; Fused
rhinophores in earlier postlarval stages and not
enclosed by the anterior notal lobes strongly point to
Notaspidea s.str. (family Pleurobranchidae); Ventral
anus in earlier postlarval stages strongly points to
Notaspidea s.str.; Posterior entire notum of middle
postlarvae without gills and gill cavity strongly points
to Notaspidea s.str.
Strong inference for the Notaspidea s.str.
cycle: Pelagic larva with spiral shell > benthic
juvenile completely loosing the shell, formation of the
solid rhinophores shifted laterally from each other by
the enclosing of the lobes of anterior notum, complete
separation of the rhinophores and oral veil, posterior
notal lobes starts to develop in earlier postlarvae and
led to dorsal anus shift and formation in juveniles
of the dorsal cavity where then three first gills
developed > benthic adult without shell, entire notum
both anteriorly and posteriorly, solid rhinophores not
connected with oral veil, dorso-terminal circumanal
gill within a special cavity.
towards to the direct development; Notum reducing;
Posterior notal lobes appearing; Gill cavity reducing;
Gills reducing; Rhinophoral pockets reducing.
Explanatory remarks: Presence of the wellestablished recapitulations of the notal and
rhinophoral patterns, and ventral position together
with the significant structural similarity of the adult
stages (presence of the notum; digestive, nervous,
reproductive systems details etc.) strongly point for
the notaspidean s.str. ancestry, closely similar to
the recent members of the family Pleurobranchidae.
Presence of the recapitulation of the juvenile gill
cavity in the juveniles of completely phanerobranch
genus Onchidoris, presence of the fully-functional
to partially reduced gill cavity in the adult stages
of some genera of so called phanerobranch group
(Onchimira, Calycidoris, Diaphorodoris), presence
of the juvenile gill cavity in the adult Loy meyeni,
presence of the partially modified semi-open gill
cavity in adult of some Corambe species strongly
point to ancestral condition of the gill cavity presence
and their further reduction as major feature of the
ingroup evolution (see below for details).
Model of the ancestral ontogenetic cycles of the
order Nudibranchia s.str. (=Cladobranchia)
Systematic diagnosis: Notum present or reduced;
Internal shell always absent; Rhinophores are well
defined, solid, connected with oral veil and partially
surrounded by lateral notal margins; Oral veil is large,
completely substitutes anterior notum. Mantle cavity
absent in all species; True gill is absent in all species;
Various secondary gills or papillae present in many
species; Genital openings on the lateral side; Jaws
monolith, well defined; Radula possess numerous
basically hook-shaped radular rows differentiated and
209
reduced in different degree (up to one teeth per row);
Central teeth present in most species; Digestive gland
is entire in few taxa, in most is branched in various
degree, in many taxa branches are penetrated to the
dorsal papillae; CNS with fused or separated cerebral
and pleural ganglia; Reproductive system is diaulic in
most species; Vas deferens is fully closed. Copulative
apparatus near female genital opening on the left side
of the body.
Aeolidiidae, Arminidae, Bornellidae, Calmidae,
Cumanotidae,
Dendronotidae,
Dironidae,
Doridomorphidae,
Doridoxidae,
Dotoidae,
Embletoniidae,
Eubranchidae,
Facelinidae,
Fionidae, Flabellinidae, Glaucidae, Goniaeolidiidae,
Hancockiidae,
Heterodorididae,
Janolidae,
Lomanotidae,
Notaeolidiidae,
Phylliroidae,
Pseudovermidae,
Scyllaeidae,
Tergipedidae,
Tethydidae, Tritoniidae.
(key phylogenetic characters): Strong oral
veil substitute anterior part of the notum; Solid
rhinophores; Solid jaws.
Model of key-transformations: Internal shell
completely disappeared (regressive); Rhinophoral and
oral apparatus accepted as direct modification of the
Pleurobranchaeidae type with addition of formation of
the solid rhinophores still integrated with the strongly
widened oral veil substitutes the anterior part of the
notum (progressive or neutral); Complete reducing
of the gill (regressive); Formation of the solid jaws
based on integration of the separated elements of the
notaspideans (progressive).
Phylogenetically important succession of
the key-characters: Anus and nephroproct still
placed laterally strongly point to Notaspidea s.str.
Well defined (though solid) rhinophores point to
Notaspidea s.str. Laterally shift rhinophores and
widened oral veil substitutes anterior part of the
notum point to particular notaspidean s.str. family
Pleurobranchaeidae. Diaulic reproductive system
points to the Notaspidea.
Recapitulations: Spiral shell of the juvenile stages
points to basal opisthobranchs like Cephalaspidea
210
s.lato (including Acteonidae) and Notaspidea;
Separated rhinophores in earlier postlarval stages
of Tritonia species and not enclosed by the anterior
notal lobes point to family Pleurobranchaeidae of
Notaspidea s.str.
Strong inference for the Notaspidea s.str. Weak
inference for the particular notaspidean family
Pleurobranchaeidae.
cycle: Pelagic larva with spiral shell > benthic juvenile
completely loosing the shell, formation of the solid
rhinophores shifted laterally from each other without
enclosing of the lobes of anterior notum, integration
of the rhinophores and oral veil > benthic adult
without shell, with reduced notum both anteriorly
and posteriorly, solid rhinophores integrated with
the widened oral veil which is substitute the anterior
part of notum, true gill completely absent, weakly
papillated lateral and dorsal notum.
towards to the direct development; Notum reducing;
Rhinophoral pockets reducing; Rhinophores
secondary united together.
Explanatory remarks. The special similarity
between rhinophoral and oral apparatus of some basal
Nudibranchia (Doridoxa, Heterodoris, Tochuina,
Tritonia) and the particular notaspidean s.str.
family Pleurobranchaeidae and ontogenetic patterns
of the rhinophores development point to possible
nudibranchs s.str. ancestry within the latter group (see
below for details).
ONTOGENETIC SYSTEMATICS OF THE
DORID NUDIBRANCHS (ORDER DORIDACEA)
As was defined above, the dorid group (here
considered as order Doridacea) possesses a set of
unique characters, including a dorsal circumanal
gill corolla integrated within posterior part of the
notum and elaborated rhinophores, integrated within
anterior part of the notum, typically within special
pockets. The oral veil of dorids is small and reduced,
anterior end of the body is the notal edge, not the
edge of the oral veil (Figs 2 D; 3 C). Dorids include
two major groups — Cryptobranchia (cryptobranch
dorids) and Phanerobranchia (phanerobranch dorids).
Cryptobranchia possess special cavity around
the gills, where the gills are able to completely
retracted (Fig. 2 D) and usually well defined notum
without posterior lobes and numerous processes.
Phanerobarnchia, by definition is completely devoid
of any gill cavity, instead gills are directly attached to
the dorsal notum and able to contract, notum usually
reduced and often posses posterior lobes or processes.
Gills morphology and digestive (except for radula)
and reproductive organs are essentially similar in
cryptobranchs and phanerobranchs.
Dorid systematics is deeply rooted in the classical
period of taxonomy (e.g. Linnaeus, 1758; Alder &
Hancock, 1864; Abraham, 1877; Bergh, 1892; and
many others), but serious evolutionary studies were
started only recently. Various classificatory schemes
and implied their evolutionary models, already have
been suggested in old works (e.g., Bergh, 1892;
Odhner, 1934, 1939), but usually without much
discussion and unequivocal set of strict evidences.
The same author can use different schemes of
classification in different works, that is especially
characteristic for the nudibranch classics Rudolph
Bergh and Nils Odhner. However, Odhner’s (1939)
system of the order Nudibranchia including four
suborders (one of which is Doridacea — dorids),
became an important base actually for all modern
classification and phylogenetic reconstructions.
The only pre-1990S challenge for the classical
Nudibranchia concept was presented by Yu.S.
Minichev and Ya.I. Starobogatov (1979). They,
however, choose similar to the classical authors
the “not much discussion” strategy, and published
already “completed” systems in the abstracts of
Soviet malacological conferences with minimum
commentaries and explanatory remarks. They
suggested numerous new taxa of the order ranks
(including super- and suborders) and completely
disregard any classical concepts of “Opisthobranchia”
and “Nudibranchia”, thus prima facie perfectly
anticipated all further both morphological cladistics
(e.g. Haszprunar, 1988) and molecular phylogenetics
(Jörger et al., 2010) central idea of paraphyly of any
traditional taxa. However, despite on this challenge,
the Minichev and Starobogatov systems remained a
“blind street” compare to the modern evolutionary
studies first of all was extremely lapidary and
actually “closed” for further discussion in persisting
of “once and for all” approach. For instance, the
systems were constructed only on the reproductive
apparatus features, and many important external
and digestive system features have been completely
omitted. At the boundary of 1980S-1990S only few
publications dealing with nudibranch macrosystems
and evolution have been further appeared (e.g.
Schmekel, 1985; Wägele, 1989a; Evolutionary
Biology of Opisthobranchs, 1991) closely approach
soon happen “phylogenetic explosion”.
Thus, accumulated to the end of XX century
knowledge on morphology of the nudibranch molluscs
was so immense, whereas number of published
evolutionary works was so scarce, that “phylogenetic
explosion” appeared as absolutely unavoidable. It was
happen mostly at the millennium boundary and was
much inspirited also by statistical approach, cladistics,
and somewhat later, by molecular phylogenetics (e.g.,
Wägele & Willan, 2000; Valdés, 2002a,b; Fahey
& Gosliner, 2004; Fahey & Valdés, 2005, Pola et
al., 2007 and many others), and not only consider
the dorids but also any other living organisms. By
current widespread opinion such combination finally
will answer on the “main evolutionary question”
and presented the exhaustive “Tree of Life” —
from Archaea to Chordata (see e.g. Maddison et
al., 2007; Philippe et al., 2011a). The challenge thus
is only increasing the number of genes used for
reconstruction, and improvement of the statistical
algorithms, etc. (e.g., Ciccarelli et al., 2006; Dunn
et al., 2008; Goloboff et al., 2009; and many others).
This problematic issues especially became clear in
211
Adult
apomorphic
p
p
character
Echinocorambe
Doridunculus Lophodoris
Corambe
character
Descendant taxon
characters
Deletion
Adult apomorphy
Juvenile
plesiomorphy
Ancestral taxon
Adult plesiomorphic
character
Figure 5:
Example of the interactions between tree and cycle: model of the independent regressive transformation (juvenilization) of the external shape of dorid
nudibranch in several families: Akiodorididae (genera Echinocorambe and Doridunculus); Goniodorididae (genus Lophodoris); Onchidorididae
(genus Corambe). I.e. in three different families of phanerobranch dorids essentially similar properties of the ancestral dorid ontogenetic cycle led to
independent appearing similarly constructed postlarvae-like adults.
the nowadays, when importance of the traditional
systematics have been challenged in favour of the
phylogenetics. Numerous researchers, working in
the field of phylogenetics usually have superficial
knowledge about tasks and methods of the traditional
systematics (i.e. systematics itself), and not rarely,
underlined in their work by the past evolutionarymorphological concepts, without understanding scale
of the past discussions. At the same time, earlier
molecular phylogenetists, were much more careful
about phylogeny reconstructions, leaving a “last plea”
for the morphology and ontogeny (e.g., Raff et al.,
1989). In this respect, quite remarkable, that famous
RNA (!) researcher Carl Woese in 2009 warned
212
about importance of the biology itself in the field of
molecular biology (see Woese & Goldenfeld, 2009).
All this can be applied to the modern dorid
systematics and phylogenetics. A good deal of modern
papers have suggested a particular consideration
on a priori decisions of character polarity (Valdés,
2002a,b; Fahey & Gosliner, 2004; Fahey & Valdés ,
2005 and others), but scarcely offer a discussion for
such decisions. That in this case difference to the past
“extremely arbitrary” implications of the traditional
taxonomy and evolutionary morphology? One of such
most controversy evaluation has received the keyfeature of the entire dorid group — gill apparatus.
Besides the traditional dorid group Phanerobranchia,
prima facie lacking any gill cavity, such feature also
characteristics for another, minor Doridacea group
–– Bathydoridoidea. That is most important, that the
latter group traditionally is always considered as an
“archaic” (Minichev, 1969). This view without critical
discussion have been accepted by the morphological
cladistics, as a plesiomorphic character, and
bathydoridids, therefore were “translated” as a
“most basal group” (Valdés, 2002a,b). This concept
of morphological cladistics was then accepted by
molecular one (Valdés, 2004). However, by definition
“cavityless” phanerobranchs have demonstrated the
presence of quite well defined gill cavities (e.g. in
the genera Calycidoris and Diaphorodoris). This
obviously important fact has received a very scarce
discussion in past (Abraham, 1876; Roginskaya,
1972; Millen, 1985) but was not considered at all by
the modern phylogenetic studies (Valdés, 2002 a,b;
Fahey & Valdés, 2005; see Martynov et al., 2009 for
further details).
Already in 1994 were obtained further evidences
for much more complicated picture of the dorid
evolution: was described an unusual corambid species
Loy meyeni, possess dorsal gills within small cavity
(Martynov, 1994a) –– the feature not only unknown
before in any corambids, but also strongly contradicts
with the diagnosis of Phanerobranchia. Furthermore,
pattern of the posterior notal lobes of Loy meyeini and
another species L. millenae was essentially similar to
the pattern known in the dorid postlarval, specimens
described earlier (Thompson, 1958). Thus, as it was
became obvious, that some important issues have
been completely omitted in the dorid systematics
and evolutionary studies because all efforts were
put on understanding of the adult stages, whereas
postlarval and juvenile stages of the ontogenetic
cycle were not considered at all. However, quite
clearly expressed implications on the paedomorphic
origin of the corambids and significant corrections
of the major trends of the dorid evolution (Martynov,
1994b, 1995) were positive noticed (Wägele & Willan,
2000) but not considered at all for the phylogeny
reconstructions. Another important implication of
the discovery of these highly aberrant corambids
was unambiguous consideration about ancestral
pattern of the cryptobranch mode (i.e. presence of
the gill cavity). Thus, step by step, was developed an
improved model of the dorid evolution (see Fig. 1),
which much better explains existence real taxa being
simultaneously “typical” phanerobranch by presence
of the radula and buccal pump, but can be also no less
better described as cryptobranch due to presence of
the gill cavity, even reduced.
Thus, the new model of the dorid evolution, which
considers properties of the entire ontogenetic cycle
(Fig. 1) implies principally different direction of the
evolution of the order Doridacea (Martynov, 1994b,
1995; Martynov et al., 2011; Martynov & Schrödl, in
press) than that was “reconstructed” by the modern
phylogenetic analysis with an invisible help of very
old and purely evolutionary morphological concept of
the “archaic” phanerobranchs (Minichev, 1969).
According to the new model, in the ancestral
ontogenetic cycle of the dorid groups (order
Doridacea) has emerged for the first time a keynovelty — mechanism of the transferring of the
anus area (i.e. area, there then gills will be formed)
from ventral to the dorsal position (see Figs 1, 2).
This mechanism implies asymmetrical growth of
the right notal posterior lobes and further formation
on this base the gill cavity (Martynov et al., 2011).
Thus, the dorid as group is clear delineated by
otherwise similar to it Notaspidea s.str., by appearing
in their ontogenetic cycle the gill cavity and separated
rhinophores as key-novelties. This also implies that
all modern cryptobranch dorids should have in their
ontogenetic cycle the peculiar stage with the posterior
notal lobes lead then to the gill cavity formation.
Such prognostic ability is another very important
differences of the ontogenetic systematics from
the current phylogenetic thinking. Taking into
consideration, that about 1.500 species of cryptobranch
dorid are currently known, but only 2-3 species have
213
been studied ontogenetically (e.g. Thompson, 1958;
Usuki, 1967; Martynov et al., 2011; this study), with
help of such prognostic model we can then infer,
that earlier postlarval stages of yet unknown other
cryptobranch also should possess such stage with the
posterior lobes. A possibility to infer other ontogenetic
stages used the known one (first of all, adults) has
already been suggested in frames of comparative and
evolutionary morphology (see e.g., Remane, 1955), but
was not then used as a routine, practical methods. Such
possibility to infer for any yet unknown ontogenetic
stage by already known is very important feature of
the ontogenetic systematics, making the systematics
itself not only purely descriptive science, as usually
considered, but instead, a science of predictions,
that then could be tested in different ways (e.g. by
study of the ontogeny of further dorid species). Most
importantly also, the such possibility to infer unknown
stages is greatly contradict to the Hennig fundamental
principle considering any organism as a just separate
semaphoront.
The new model of the dorid evolution has also
several different important implications. First of all,
the essential similarity of the ontogenetic pathways in
the different cryptobranchs (e.g. so different groups
as Chromodorididae and Discodorididae) implies
potential possibility for further independent, parallel
appearing in non directly related dorid subgroups, of
heterochronic regressive variants, from “moderate”,
when only gill cavity not develops in adult organisms
(i.e. most species of the family Onchidorididae), to
“radical”, then clear earlier postlarval features (notal
lobes) appeared in the adult stages. Reality of the
independent heterochronic shifts underlying by the
common ontogenetic cycle in dorids have been already
demonstrated both structurally and phylogenetically
(Martynov, 2000; Millen & Martynov, 2005; Martynov
et al., 2011): corambid group (family Onchidorididae)
and the genus Echinocorambe (Akiodorididae)
have reached externally very similar juvenile-like
adult organization, whereas internal features still
preserve unique pattern of radula and buccal pumps
of onchidoridid and akiodoridid respectively.
214
Another very important implication of the
new ontogenetic model of the dorid evolution is its
possibility to find traces (i.e. recapitulations) of the
initial cryptobranch mode of the gill formation in
the earlier postlarval stages of phanerobranch dorids,
which are completely lacking any gill cavity at the
adult stages (Martynov et al., 2011).
Finally, the new model greatly contradicts with
widely accepted considerations about primary
condition of the gill cavity absence in the dorid
group Bathydoridoidea (Minichev, 1969; Wägele,
1989a; Valdés, 2002 b). There is no any ontogenetic
information on the bathydoridid groups currently.
However, apart form the absence of the gill
cavity, bathydoridids demonstrated number of other
reduced features: the notum is completely reduced
in the Bathydoridoidea, but leave a clear border
between lateral body wall and dorsal side (see, e.g.
Wägele, 1989b). This fact quite clearly points toward
considering this feature as a secondary reduced instead
of a primary one. Bathydoridids also are completely
devoid of the rhinophoral pockets — a feature that
usually points to reduction in other phanerobranchs.
Until recently bathydoridids were considered as
having diaulic reproductive system (Odhner, 1934;
Minichev, 1969; Wägele, 1989a). It was used for
further evidence of clear separation of Bathydorididae
from other dorids, and most likely also as an archaic,
basal feature (e.g. Wägele, 1989a; Wägele &
Willan, 2000). However, 9 years ago was described
Bathydoris spiralis Valdés, 2002 (Valdés, 2002b),
the first bathydoridid with a triaulic reproductive
system, i.e. as in other dorids. The gill apparatus of B.
spiralis is very similar to the compact gill corolla of
other dorids, and quite different from the “disperse”
gill placement of most other species of the genus
Bathydoris. Two groups have been already recognized
within bathydoridids (Valdés, 2002b). One group of
species of the genus Bathydoris (including diaulic
Bathydoris clavigera and triaulic Bathydoris spiralis)
possesses eyes and a relatively low body, whereas
the majority of other Bathydoris species, like B.
abyssorum Bergh, 1884 and, B. ingolfiana Bergh,
1899, do not have eyes and their body became very
high, almost sphere-shaped, what is very unusual for
dorids. Intriguingly, those species having eyes and
low body inhabit relatively shallow depth of 40–500
m, whereas eyeless species with spherical body are
known from much deeper environments, up to 4500
m (Bathydoris abyssorum).
In absence of an elaborated model of the dorid
evolution and underlying by formal approach
of phylogenetic systematics, the findings of the
unique triaulic Bathydoris spiralis with typical
for the many dorids circumanal gill corolla, the
characters which are clearly connected small group
Bathydoridoidea with 2000 other dorid species,
did not lead, nevertheless for the consideration of
which species as a transitional taxon or “missing
link”. Instead main conclusion of the single available
phylogenetic analysis of bathydoridid including B.
spiralis (Valdés, 2002b) became their paraphyly.
Shallow-water species turned to be a sister-group
for the usual phanerobranch dorids, however these
groups share only absence of the gill cavity. I.e. the
resulting tree actually has showed the similarity of the
bathydoridids and all other dorids, however, implicit
model of the ancestral mode of the phanerobranch
dorids led to their incorrect interpretation. The results
were truly paradoxical and required creation within
single genus Bathydoris, not only new genera and
families, but potentially, even suborders (!), to show
the tree pattern in the system of categories (Valdés,
2002b). Nevertheless, some bit of absurdity of such
potential decision was clear, and in the cited paper
there were not suggested any new even generic
names, but the case was discussed and interpreted as
failure of the traditional systematics, hardly allowed
true, phylogenetic interpretation at the present stage
of knowledge (Valdés, 2002b). The final conclusion
to consider the genus Bathydoris as a paraphyletic
complex s.l. not resolved any of the problematic
issues and still there no any study attempting to make
further solution for this remarkable case.
At the same time, if interpreting historical
development of the group Bathydoridoidea
according to the new model of the dorid evolution,
these apparent paradoxes mostly disappeared.
Ancestor of the bathydoridid, should most likely
have gill cavity and free notal edge. Increasing
degree of adaptations to the more and more deep
water conditions led to consequential reductions
of the gill cavity, notum, eyes and appearing in
the most deep-water species this specific sphereshaped body (possible a response for the pressure).
According to this model, omniphagy of the
genus Bathydoris, considered as a plesiomorphic
character for all dorids (Valdés, 2002b, 2004), is
only a very special adaptation of the very restricted
in species number Bathydoris for the poverty of the
food resources in the abyssal environment, when
used any available benthic material. Bathydoridids,
thus, judged from their many unique characters is a
monophyletic group, but incorrect previous model
of their evolution led to incorrect conclusion of
their paraphyletic status.
Thus, one of the most important implications
of both ontogenetic systematics and new model of
the dorid evolution, it their prognostic ability, i.e.,
in the case of dorids, the possibility to predict real
existence of several transitional taxa (“missing
links”), combining of the presence of the gill
cavity (diagnostic feature of Cryptobranchia) with
various specific characters of the phanerobranch
dorids (lacking any gill cavity by definition).
Despite that it will be may be considered as a
purely hypothetic field, many facts, instead speak
in favour of such approach. One of such most
remarkable case, when already constructed model
of the dorid evolution has found strong support in
new independent finding of Onchimira cavifera,
having both well-defined full-functional gill
cavity and simultaneously very special radular and
buccal pump features, allowing unambiguously
to place this truly cryptobranch taxon into the
phanerobranch family Onchidorididae (see
Martynov et al., 2009).
215
Table 1:
Prognostic table for the group Doridacea
Gills present, anus dorsal
Gill cavity
Gill cavity
present
absent
Genus yet unknown (Bathydorididae),
Bathydoris (Bathydorididae)
All Cryptobranchia,
Genus yet unknown (Hexabranchidae), Hexabranchus (Hexabranchidae),
Onchimira, Calycidoris, Loy
Acanthodoris, Onchidoris, Adalaria
(Onchidorididae)
(Onchidorididae),
Genus yet unknown (Akiodorididae)
Akiodoris, Doridunculus
(Akiodorididae),
All Polyceridae,
Genus yet unknown (Gymnodorididae) Gymnodoris, Analogium
(GymnodoriGLdae)
Gills present, anus ventral
Corambe (Onchidorididae)
Corambe s.str. (Onchidorididae),
Echinocorambe (Akiodorididae)
Gills absent, anus dorsal
Vayssierea (Vayssiereidae)
Phyllidia,
Phylidiella, Phyllidiopsis etc.
(Phyllidiidae)
Gills absent, anus ventral
Impossible combination?
All these facts are of course intriguing but there
is no any (at least explicit) prognostic in the modern
systematics, both “traditional” or “phylogenetic”,
though few exotic attempts to produce a “periodical
systems” for taxonomy have been performed
in past (e.g. Schimkewitsch, 1906, 1909). Here,
therefore, will attempted to challenge this, and gave
further evidence for the validity of the ontogenetic
systematics by presenting a special application,
that is almost completely absent in the modern
systematics and phylogenetics: the prognostic table
(see Table 1).
216
Fryeria
ARE THE TRADITIONAL NUDIBRANCHIA
MONOPHYLETIC?
As defined above, the traditional order
Nudibranchia is here considered as two independent
groups (orders): Doridacea and Nudibranchia s.str.
(equal to the Cladobranchia). What was the reason for
that, except for briefly outlined above in the diagnosis
and the model transformations? The traditional
group Nudibranchia despite of numerous attempts
to challenge it (for instance, Marcus & Marcus
(1967) used a system of four independent orders
corresponding to the four suborders of Nudibranchia;
Minichev & Starobogatov (1979) not used the name
Nudibranchia at all), nevertheless recently received
status of monophyletic according to a morphological
cladistic study (Wägele & Willan, 2000), and still no
unambiguous molecular evidences for their paraphyly
(see Jörger et al., 2010 vs. Grande et al., 2004).
In the morphological phylogenetic analysis
(Wägele & Willan, 2000) indicated only 4
autapomorphies for Nudibranchia: 1. Solid
rhinophores; 2. Absence (by loss) of the shell; 3.
Longitudinally situated pericardium; 4. Presence of
special vacuolated epithelium. However, uniqueness
of most of these characters, their importance as
the indicators of the monophyletic group may be
questioned. First of all the loss of shell is really not
possible to discuss as any key-characters since it
happened many times independently within various
Opisthobranchia. Formation of the solid rhinophores
on the base of the enrolled chemosensory organs of the
notaspideans is also not unique for the Nudibranchia,
and clearly independently has taken place within
the group Saccoglossa (e.g., Jensen, 1996) and
acochlidians (Schrödl, Neusser, 2010). In a similar
way, another listed nudibranch autapomorphy — the
longitudinally situated pericardium also independently
appeared within Sacoglossa and acochlidians.
Finally, the vacuolated epithelium occurrence and
functions remains very scarcely studied regarding its
phylogenetic importance. Even, based on exclusively
structural, systematical approach, traditional
Nudibranchia are very heterogeneous. The group
of dorids, from one side, and three other traditional
suborders of the Nudibranchia (Dendronotacea,
Arminacea and Aeolidacea, all three suborders also
have been united under the name of Cladobranchia)
have so many important differences regarding both
external and internal (digestive and reproductive
systems) characters, that make unification these
groups under one name problematic. Is it however
some promising set of structures that may be used
for at least potential assessment of the para- or
monophyletic status of Nudibranchia?
Interesting material for such analysis available
from another external key nudibranchs feature —
rhinophores. The small relic group Notaspidea s.str.
is well established as ancestral or sister taxon for the
Nudibranicha (Thiele, 1931; Tardy, 1970; Martynov,
1999; Wägele & Willan, 2000; Martynov & Schrödl,
2008; present work). Both adult notaspids of the family
Pleurobranchidae and earlier postlarval specimens of
the order Doridacea (Figs 2; 3 A, B) possess similarly
constructed, united together rhinophores, without
special pockets, because anterior parts of the notum yet
not enclosed it, as in the adult dorids. Thus the anterior
edge of the body of adult dorids is always the anterior
edge of the notum, whereas the oral veil is reduced and
remained under the anterior part of the notum.
In this respect quite remarkable and until
recently never considered is the fact of the significant
similarity in the general rhinophoral patterns between
one of the notaspid family — Pleurobranchaeidae
and most of the subgroups of the traditional
Nudibranchia, excluding the dorids. If in Doridacea
anterior notal edge enclosed the rhinophores and
then separate initially common structures of the
rhinophores itself and oral veil (Figs 2D; 3C), in one
of the notaspid family, Pleurobranchaeidae, oral veil,
instead, considerably widened, whereas anterior part
of the notum is reduced. As result, rhinophores are
considerably shifted laterally, and anterior edge of the
oral veil (!) became anterior edge of the body instead
of notum as in dorids (Compare Figs 3 A–D and 3 E).
Most remarkably, that several obviously basal
in cladistics terms (see e.g. Schrödl et al., 2001),
but not related directly nudibranch genera, i.e.
Tochuina and Tritonia (both belong to the traditional
suborder Dendronotacea), and Heterodoris and
Doridoxa (traditional suborder Arminacea) have
amazingly similar to the family Pleurobranchaeidae
rhinophoral apparatus, including wide oral veil
and reduced anterior notal edge (Compare Figs
3 E and 3 F). I.e. in the basal genera of at least
two major traditional groups of Nudibranchia —
Dendronotacea and Arminacea anterior edge of the
217
oral veil is anterior edge of the body, exactly as in
the family Pleurobranchaeidae (see also Martynov
& Schrödl, 2008). The difference between adult
morphology of the rhinophoral apparatuses of
the notaspidean families Pleurobranchidae and
Pleurobranchaeidae (Compare Figs. 3 A and 3 E)
has also remarkable correspondence in the ontogeny.
In the postlarval specimens of Berthella californica
(family Pleurobranchidae) anterior edge of the notum
further grows and partially covers rhinophores
and oral veil (LaForge & Page, 2007), whereas in
postlarval specimens of Pleurobranchaea japonica
anterior part of notum reduced, and remained
notum fused with the posterior part of the oral
veil (Tsubokawa & Okutani, 1991; Gibson, 2003).
As already well established (Thompson, 1958;
Usuki, 1967; Martynov et al., 2011; present study),
earlier postlarval stages of both, cryptobranch and
phanerobranch dorids have principally similar to
the adult and postlarval notaspid of the family
Pleurobranchidae pattern of the united rhinohores
not enclosed by the anterior notum (Compare Figs
3 A and 3 B).
On the contrary, postlarval ontogeny of
Tritonia hombergi (Nudibranchia: Dendronotacea),
rhinophores, compare to the both dorids and
notaspids do not demonstrate a stage with united
rhinophores at all, but instead, they appeared
initially already very separate from each other,
at the lateral edges of future oral veil and lateral
parts of the notum (Thompson, 1962). Thus, the
only principal difference otherwise very similar
rhinophoral apparatuses of Pleurobranchaeidae
and non-dorid nudibranchs — presence in the
latter group of solid rhinophores. However, it is
not prevent for further originating of the solid
rhinophores on the base of the enrolled as it was
definitely took place independently in Sacoglossa.
In this respect, the ontogenetic mechanism of the
rhinophores development in Tritonia, without stage
with the unite rhinophores, may be an important
evidence that such pattern is further modification of
exactly Pleurobranchaeidae-like notaspids, which
218
have separated rhinophores at adult stage but yet
united in the postlarval ontogeny. Rhinophoral
development of Tritonia appeared thus as secondary
modification of the ontogeny of Pleurobranchaeidae,
but in which the stage with united rhinophores was
further deleted. If Tritonia is a descendant of the
dorid-based ontogenetic cycle, it is more likely that
stage with the united rhinophores should be persists
in it, which is not the case.
Thus a scenario implies that traditional
Nudibranchia is heterogenous group in the terms of
traditional systematics and paraphyletic in cladistics’
view (Martynov, 1999) can not be completely excluded.
For further proof of above described ontogenetic
patterns it is highly necessary modern studies of the
postlarval ontogeny of some basal nudibranchs, and
also search for additional characters that potentially
can share Pleurobranchaeidae and basal Nudibranchia.
At least, in non-dorid nudibranchs there is the clear
pleurobranchid character — lateral position of
anus. Basal nudibranch genera, such Heterodoris
and Doridoxa, are without secondary respiratory
structures, thus is possible to consider these taxa as
modifications of the ancestral ontogenetic cycle of the
Pleurobranchaeidae, in which regressive heterochronic
event of the true gill reduction took place.
CONCLUDING REMARKS
Under approach of the ontogenetic systematics
quite senseless to speak about just “plesiomorphic”
or “apomorphic” states (two basic terms of the
morphological phylogenetics). Instead much more
productively to specify that was common ancestral
juvenile condition (i.e. juvenile plesiomorphic
state) and that was ancestral adult condition (i.e.
adult plesiomorphic state) (see Figs 4, 5). Further
heterochronic shifts towards juvenilization of the
adult morphology might, for instance, produce similar
juvenile adult morphology many times independently in
different families, strongly underlined by the common
ancestral ontogenetic cycle and it is well supported, e.g.,
in dorid nudibrancs, by unique morphological markers.
Thus, ontogenetic systematics does not disregarded
trees as useful representation of the evolutionary
process, but instead makes phylogenetic terminology
and conclusions much more precise, thus highlights
the integrative interactions between the “cycle” and the
“tree” (Figs 4, 5).
The “cycle-thinking” implies thus thinking in
the term of newly emerged characters and particular
functional organizations in any taxa, even currently
completely extinct, with recapitulation on limited
distance as “reference points” in the evolutionary
succession of each preceding and next ontogenetic
cycle-taxon. In this respect, the above demonstrated
key-novelties have well characterized Notaspidea
s.str., Doridacea and Nudibranchia s.str., but failed to
found a reasonable ground in the purely phylogenetic
conception “Nudipleura”, overwhelmingly merged all
these quite well defined separate taxa and obscure
potential paraphyletic status of traditional (and still
accepted as monophyletic) Nudibranchia s.l.
ACKNOWLEDGEMENTS
I am sincerely grateful to T.A. Korshunova
(Institute of Higher Nervous Activity and
Neurophysiology, Russian Academy of Sciences,
Moscow) for her generous help in research. My
particular gratitude for long term collaboration is due
to Michael Schrödl (Zoologische Staatssammlung,
München). Special thanks to organizers of the 3th
IWO, very successful both scientifically and culturally
meeting, and particularly, to Jesús S. Troncoso
(University of Vigo). Hans Bertsch (Universidad
Autónoma de Baja California) is thanked for kind
discussions. Specialists of the Interdepartmental
Laboratory of Electron Microscopy (Biological
Faculty, Moscow State University), including head
of laboratory G.N. Davidovich, chief engineer
A.G. Bogdanov, and researchers Yu.V. Golubtsova
and A.M. Kusnetsova, provided all the necessary
conditions for the study of morphological structures.
This study was supported by DFG grants no. SCHR
667/6–1 and SCHR667/10–1.
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Thalassas, 27 (2): 225-238
BEHAVIORAL ADAPTATIONS IN RELATION TO LONG-TERM
RETENTION OF ENDOSYMBIOTIC CHLOROPLASTS
IN THE SEA SLUG Elysia timida
(OPISTHOBRANCHIA, SACOGLOSSA)
VALÉRIE SCHMITT (1, 2) & HEIKE WÄGELE (1)
Key words: Sacoglossa, endosymbiosis, chloroplasts, retention, phototaxis, photobehavior.
ABSTRACT
A comparative study was performed to analyze
differences in evolutionary adaptations in two sea
slug species, Elysia timida with long-term retention of
endosymbiotic chloroplasts and Thuridilla hopei with
short-term retention of endosymbiotic chloroplasts.
Both sacoglossan species stem from the same habitat
and show similar body sizes and structures with
parapodial lobes whose position can be actively
varied by the slugs. Ethological analyses were carried
out concerning the positioning of parapodia and
other photobehavioral parameters like phototaxis. In
parallel, photosynthetic activity was measured with
a Pulse Amplitude Modulated Fluorometer (PAM).
In total, 252 E. timida individuals and 63 T. hopei
individuals were included in the analysis. Slugs
were collected diving in shallow depths up to 5 m in
Banyuls sur mer, France, and kept in the laboratory
(1) Zoologisches Forschungsmuseum Alexander Koenig
Adenauerallee 160. 53113 Bonn. Germany
Tel: +49 (0)228 9122 241
Fax: +49 (0)228 9122 202
Email: [email protected]
(2) Observatoire Océanologique, 66651 Banyuls sur mer, France
Corresponding author: Valerie Schmitt
in basins with running seawater and natural light
through a glass window. Behavioral observations
and PAM-measurements were performed in 4 time
intervals in the course of an observation day in
daylight and dark-adapted conditions. Phototactic
behavior was found to be present in both compared
species, although the phototactic reaction was
more pronounced in E. timida. Phototaxis was also
observed in juvenile E. timida before sequestration
of first Acetabularia-chloroplasts, which indicates
no direct current influence of the endosymbiotic
chloroplasts. Other parameters, however, like the
positioning of the parapodia, were observed to
be significantly different between the long-term
and short-term storing species. While an adapted
changing of the parapodia’s position in reaction to
light conditions was not observed in T. hopei, the
typical specialized photobehavior of E. timida with
active variation of parapodial positions including
exposure and protection of integrated chloroplasts
could be confirmed and analyzed in this study.
Positioning of the parapodia in E. timida showed
a significant relation to fluorescence values from
PAM-measurements demonstrating the efficiency of
exposure and protection of embedded chloroplasts.
225
VALÉRIE SCHMITT & HEIKE WÄGELE
Figure 1:
a Thuridilla hopei on Dictyota (not a food organism of this species). b Elysia timida on its natural food alga Acetabularia acetabulum.
c Elysia timida, parapodial opening level 2. d Elysia timida, parapodial opening level 3. e Three juveniles attached to a young Acetabularia: on the
left two specimens before feeding, on the right one specimen after feeding
The specific photobehavior of E. timida with
controlled exposure of parapodial lobes represents a
highly specialized evolutionary adaptation in relation
to long-term integration of chloroplasts and - state of
the art - is only recorded for this species.
INTRODUCTION
Our knowledge on biology and evolution of
functional kleptoplasty in various sacoglossan
sea slugs has increased lately to a considerable
extent (see e.g., Giménez Casalduero and Muniain,
2008; Händeler et al., 2009; Jesus et al., 2010 and
literature herein). But when it comes to behavior,
226
our knowledge is still limited. Sacoglossans reveal a
variety of evolutionary adaptations when it comes to
retain endosymbiotic chloroplasts – especially with
regard to behavior. First descriptions of specialized
photobehavior in sea slugs were done by Fraenkel
(1927) when he examined photomenotaxis in Elysia
viridis. In a later study comparing five sacoglossan
species, the focus was laid on the presence or absence
of endosymbiotic chloroplasts in the sea slugs. Three
symbiotic species with integrated chloroplasts (Elysia
tuca, Costasiella lilianae (= Costasiella ocellifera
after Clark (1984)), and Elysia crispata) and two
aposymbiotic species (Oxynoe antillarum and
Berthelinia carribea) were analyzed concerning their
BEHAVIORAL ADAPTATIONS IN RELATION TO LONG-TERM RETENTION OF ENDOSYMBIOTIC CHLOROPLASTS
IN THE SEA SLUG Elysia Timida (OPISTHOBRANCHIA, SACOGLOSSA)
photobehavior (Weaver and Clark, 1981). As one
result, the symbiotic species oriented towards light
while the aposymbiotic species avoided light which
points to a possible relationship between symbiotic
chloroplasts and phototaxis.
this behavior. During our studies we analyzed these
varying positions in relation to irradiance and tested
both species for the presence of phototaxis.
The chloroplast-hosting sacoglossan Elysia timida
has a specially notable photobehavior, changing the
position of its parapodial lobes from a contracted,
closed posture to a spread, opened leaf-like posture
(Rahat and Monselise, 1979). As E. timida varies
the position of the parapodia as a reaction to light
conditions, a possible nearby conclusion is that this
photobehavior could have evolved in relation to the
chloroplast-endosymbiosis. E. timida is a common
Mediterranean species that lives in a close relationship
to its food alga Acetabularia acetabulum from which
it retains its endosymbiotic chloroplasts (Marin and
Ros, 1992; Marin and Ros, 1993). With an extensive
duration of approximately three months of retaining
the endosymbiotic chloroplasts functional during
starvation, E. timida belongs to the few species with
the most extended capability of long-term retention
of chloroplasts (Evertsen et al., 2007; Giménez
Casalduero and Muniain, 2008; Händeler et al., 2009;
Wägele et al., 2010). Recent literature defines longterm retention as lasting functionality of chloroplasts
of more than a month opposed to short-term retention
lasting about one week (Händeler et al., 2009).
In total, 252 Elysia timida and 63 Thuridilla
hopei (Fig. 1a and b) were collected in the same
habitat in Banyuls sur mer, France, by diving in
shallow depths down to about 5 m, in July 2009
and September 2010. Individuals were kept in the
laboratory (Observatoire Océanologique, Banyuls
sur mer, France) in basins of about 160 cm x 60 cm
with running seawater from the laboratory circulation
system (21.2 ± 1.0 °C in July 2009 and 19.6 ± 0.9 °C
in September 2010). It was attempted to provide the
animals semi-natural conditions with exposure to
natural (but not direct sun-) light through a window
(orientated to the west) with a light intensity of up to
47 and 37 μmol quanta m-2 s-1 (PAR: photosynthetic
active radiation, highest single values measured
in July 2009 and September 2010, respectively).
Free access to an assortment of various algae from
their natural environment, including the preferred
food algae Acetabularia acetabulum (E. timida)
and Cladophora cf. vagabunda (T. hopei) (Marin
and Ros, 1989) collected from the same collection
sites as the animals, was provided. For the various
photobehavioral experiments, algae were removed
from the basins and running sea water supply was
stopped in order to exclude any additional influencing
factors. Clutches laid by E. timida individuals in the
laboratory were kept in petri dishes with artificial
sea water and regular water exchange until hatching.
Until experiments started, the juveniles were kept in
artificial seawater with no food provided. In this state,
juveniles are transparent (Fig. 1 e).
As the special photobehavior of E. timida
should be analyzed in more detail in this study with
regard to its relation to the long-term integration
of endosymbiotic chloroplasts, it was compared to
a similar Mediterranean species with short-term
retention of chloroplasts. The sacoglossan Thuridilla
hopei is a species with short-term chloroplast
endosymbiosis (Marin and Ros, 1989; Händeler et al.,
2009) and was chosen as the most suitable comparative
species, as both E. timida and T. hopei are common
Mediterranean species that live sympatrically and
have about the same body size and structure with
parapodial lobes that can be actively closed and
opened by the slugs - the basis for the comparison of
First phototaxis study: Elysia timida
The first observations on phototactic behavior
included two groups of 50 individuals each in two
separate basins. The two basins were both orientated
parallel to the window side and for the trial were
covered each half with black board. As a result, each
227
a
Day 1
Trial 1
Trial 2
Natural light
Starting point of
individuals
under the cover
Natural light
Window
Window
Basins
Basins
Cover
Cover
Day 2
Trial 3
Trial 4
Natural light
Natural light
Window
Window
Basins
Basins
Cover
Cover
b
Trial 1
Trial 2
Natural light
Window
Petri-dish
Natural light
Window
Petri-dish
Figure 2:
Schemata of phototaxis experiments. a First and second phototaxis study.
The first phototaxis study with 100 Elysia timida was started by covering the inner sides of the basins and putting 50 individuals each in the middle
of the dark covered side of the respective basin (indicated with a grey dot). Cover was changed after 3.5 h to the other side of the basin for the
second trial. The next day the experiment was repeated with reversed sides. For the second phototaxis experiment with E. timida and Thuridilla
hopei, the procedure of the first day of the first experiment was performed again in the same way.
b Phototaxis experiment with juvenile E. timida.
20 juvenile E. timida were put into one half of a petri-dish which was covered with black paper leaving only a gap of about 1cm for light incidence of
natural light through a glass window. The cover was first put on the one side for the first trial, and then changed to the other side for the second trial.
half of the basins was shaded while the other half
was illuminated by natural light through the window
in the same angle. The first trial was started with
covering the right half of the left basin and the left
half of the right basin (Fig. 2 a). After 3.5 hours the
cover was changed to the respective other side of the
basin and observations were continued for another 3.5
hours. On the second day, the same procedure was
228
performed in the reversed way starting with covering
the outer sides of the basins first, then changing after
3.5 hours. Thus, in total four trials were performed
in two days. This experimental design was chosen
in order to equalize any influence from different
angles of light incidence or potential other influences
from position conditions. The basins were covered at
11 a.m. at each observation day. Before starting the
100
90
80
slugs iin light [%]
70
60
trial 1
trial 2
trial 3
trial 4
50
40
30
20
10
0
0
30
60
90
120
150
180
210
time [min]
Figure 3:
Phototaxis in Elysia timida.
Two 160 x 60 cm basins were each covered half with black board and 50 Elysia timida individuals were placed under the cover on the dark side of
each basin. Every 30 min. until 210 min. locations of specimens were recorded (trial 1). Then the cover was put to the other half of the basin and
location recorded until after 210 min. (trial 2). Trial 3 and 4 were performed in the same way.
experiment, the 50 individuals were placed each in
the middle of the shaded half of the basin. Starting
with 30 minutes after the basins were covered,
individuals that had crawled into the illuminated side
were counted. The census was repeated every 30
minutes for 3.5 hours for each trial – in total 7 counts.
Second phototaxis study: Elysia timida – Thuridilla
hopei
The same trial was performed another day to
compare the phototactic behavior in E. timida and
T. hopei. For this, 77 E. timida and 48 T. hopei were
allocated into a group of 40 E. timida and 15 T. hopei
in one basin and a group of 37 E. timida and 33 T.
hopei in the other basin. The basins were covered
with black board in the same way as in the first
phototaxis trial and the trial was also started at 11 a.m.
Again individuals were placed in the middle of the
shaded half of the basin. Observation intervals were
shortened to 15 minutes and the cover was changed to
the other side already after 90 minutes in adaptation
to the results of the first phototaxis trial, which had
shown that the examination of the phototactic reaction
is possible in a short observation period.
Third phototaxis study: juvenile Elysia timida
Six days after hatching of veliger larvae had
started in the clutch, 20 juveniles which had turned
into the crawling juvenile state were put into a small
petri-dish and observed through a stereomicroscope.
The petri-dish was covered on the sides and from
upside with black paper so that only a small gap of
approximately 1 cm was left open to natural light
through a glass window (Fig. 2 b). In correspondence
with the former phototaxis studies, the juveniles
were put under the cover on the dark side and after
30 minutes it was counted how many individuals had
moved to the light-exposed area. The cover was then
changed to the other side without moving the petridish to repeat the trial in the reverse way. Again, the
number of individuals which had moved into the light
after 30 minutes was evaluated.
Studies on specialized photobehavior
Two trials were performed to analyze the
correlation of the parapodial opening and the ground
fluorescence: the first contained 25 adult specimens of
E. timida together with 15 adult specimens of T. hopei,
the second trial was performed with 50 individuals
229
of E. timida by measuring with a higher sensitivity
of the PAM (see below). For the trials, individuals
were kept in the basins separated individually in
conform containers made out of transparent plastic
bottles. Wholes were pierced equally into three rims
of each bottle in distances of about 1 cm, permitting
exchange of water from the running seawater (mean
temperature during the hours of observation 21.5 ±
0.4 °C in July 2009 and 19.8 ± 0.1 °C in September
2010). Each container was stabilized with a stone,
which also provided an opportunity for the slugs
to hide underneath. Behavioral observations were
performed along with PAM-measurements 4 times
during an observation day during the time spans 9 a.m.
– 12, 12 – 3 p.m., 3 p.m. – 6 p.m. and 6 p.m. – 9 p.m..
Opening level of the parapodial lobes was defined in
the following 6 levels and documented in correlation of
light intensity (measured in μmol quanta m-2 s-1):
0 – parapodia completely closed, the inside of
the parapodia is totally covered, slug may be
contracted
1 – parapodia are mainly closed with rims of both
parapodia coming together over the body for the
most part, but opened only a small part so that a
little area of the dorsal body can be seen (Fig. 1a)
2 – parapodia are mainly opened, but still the rims of
the opposing parapodia touch at least at one, often
at two areas, the usual position while crawling
(Fig. 1c)
3 – parapodia are opened, the rims of the opposing
parapodia do not touch, but still the angle of the
parapodia is more upward than sideward (<45°),
hence the insides of the parapodia are only partly
exposed (Fig. 1d)
4 – parapodia are fully opened, the angle of the
parapodia is more sideward than upward (>45°),
the rims of the parapodia are still either a little
upward or undulated (in contrast to 5)
5 – parapodia are fully opened and absolutely
outstretched and flat, angle is totally sideward
(90°), the rims of the parapodia are smooth
and fully expanded, sometimes even pointing
downwards (>90°)
230
In parallel, fluorescence was measured with the
help of a PAM to examine the relation between
opening level of parapodia and efficiency of exposure
of the chloroplasts.
PAM-measurements
The maximum quantum yield of fluorescence
for Photosytem II and ground fluorescence was
measured with a Pulse Amplitude Modulated
Fluorometer (Diving PAM, WALZ, Germany) during
the experiments for the observation of specialized
photobehavior. Measurements were performed 4
times per observation day (during the 4 time spans
9 a.m. – 12, 12 – 3 p.m., 3 p.m. – 6 p.m. and 6
p.m – 9 p.m.). Animals were not dark acclimated
before measurements in order to obtain the actual
fluorescence with regard to actual light intensity
and parapodia positions. The maximum quantum
yield of fluorescence for PSII in ambient light can
be defined as (Fm’ – F0’)/Fm’ (Wägele and Johnsen,
2001; Jesus et al., 2010) and shows the photosynthetic
activity in the actual light regime as a relative value.
During measurement, the maximum fluorescence
(Fm) is induced by a saturation light pulse triggered
by the PAM. The ground fluorescence (F0) measured
directly before the saturation pulse reflects the actual
fluorescence under the given light regime. Both
values depend on quality and quantity of chloroplasts.
But it has to be kept in mind that accurate estimations
of fluorescence values may be difficult to obtain
and are influenced by other factors (see Wägele and
Johnson, 2001). Only two measurements after 6 p.m.
in the second study were performed dark-acclimated
for comparison.
The fibre optic was held above the animal with a
distance of 1 cm in the region of the body part with the
parapodia. Since the size of the measured animals was
around 10 mm and the head has not to be included in
the measurements, the sensor with a cross section of
5 mm covered the body area with the parapodia well.
The second study on the relation of parapodial
opening was performed with increased sensitivity
of the PAM by putting the parameters ‘outgain’ and
‘measure-int’ from level 2 (default) to level 8 during
the whole study.
Ambient light conditions were measured with the
light sensor of the PAM.
Statistical analysis
Statistical analysis was performed using Excel
and SPSS.
RESULTS
Phototaxis
The first four observational trials to investigate
phototaxis in 100 E. timida individuals revealed
a very distinct and fast phototactic reaction for E.
timida (Fig. 3). In the first census, 30 minutes after
the slugs had been put under the cover in the basin, the
majority of individuals (ranging from 59-75% in the
four trials) had already moved from the dark covered
side of the basin into the light.
The slugs then stayed in the light-exposed areas
while the remaining individuals from the dark
followed subsequently. When the cover was changed
to the other side of the basin, the same fast movement
into the light was observed again. Repeating the trial
with reversed sides in trial 3 and 4, the reaction was
identical. After 3.5 hours of observation in each of the
four trials, nearly all of the individuals (ranging from
91-95% in the four trials) were positioned in the lightexposed area of the basin. Only a small percentage did
not enter the light side or moved back under the cover.
Those individuals were found to be in the border area
directly under the rim of the cover where a small
amount of light was falling in.
As in this first phototaxis study it became obvious
that the phototactic reaction is performed fast and
can be examined in a short observation period, the
time spans of the second phototaxis study were
adapted and shortened to observation intervals of 15
minutes and an overall duration of 90 minutes per
trial. In this second phototaxis study with the aim
to compare phototactic reactions in E. timida and T.
hopei, phototactic behavior was also seen in T. hopei
although it was obviously more pronounced in E.
timida (Fig. 4 a and b).
While after 30 minutes the phototactic reaction
of E. timida was similar as in the first phototaxis
study (mean value of 63% in the two trials compared
to 68% in the four trials of the first study), it was
slightly lower in T. hopei with 50% of individuals
counted on the light-exposed side. After 90 minutes,
E. timida revealed again a comparable result to that
in the first study with 81% of the individuals located
on average in the light area compared to 86% in the
first four trials. In T. hopei, however, the phototactic
reaction was clearly less pronounced with only 59%
of individuals positioned on the light side. Similar as
in the first study with exclusively E. timida, also in
this experiment remaining individuals of E. timida
and T. hopei were found to be in the partly illuminated
border area directly under the rim of the cover. Thus
T. hopei showed a stronger tendency to prefer this
border area with only a small amount of light falling
in while E. timida showed a stronger tendency to
prefer the area which was fully illuminated with
moderate natural light.
Juvenile E. timida, which had reached a crawling
state, but had no possibility yet to feed on Acetabularia
acetabulum, also revealed a distinct phototactic
behavior. In both trials with changing the cover from
one side to the other like in the studies before, 90%
and 95% (respectively) of the 20 juveniles had moved
into light after 30 minutes which reflects a very fast
and distinct phototactic reaction.
Specialized photobehavior
The individuals of E. timida varied their
parapodial positions from a nearly closed condition
to fully spread leaf-like positions ranging from
parapodial opening level 1-5 (Fig. 5 a and b). A
complete closure (level 0) was not observed during
the trials, but during night and extreme light exposure
231
a
100
90
slugs in light [%]
80
70
60
E timida
T hopei
50
40
30
20
10
0
0
b
15
30
45
60
75
90
time [min]
100
90
80
slugs in light [%]
70
60
E timida 2
T hopei 2
50
40
30
20
10
0
0
15
30
45
60
75
90
time [min]
Figure 4:
Phototactic reaction in Elysia timida and Thuridilla hopei.
The experiments were performed with 77 Elysia timida and 48 Thuridilla hopei in two basins. a First trial with cover on the inner side. b Change of
cover to the outer side (after 90 min). Observation intervals were shortened to 15 minutes and duration of one series was limited to 90 minutes.
(not figured here). T. hopei, however, did not show
a higher parapodial opening level than 1 (Fig. 1a)
during the observations irrespective of irradiance
(Fig. 5 a). In the majority of cases (112 out of 120
observational cases), the parapodia were closed (level
0). To examine the ability to open the parapodia, T.
hopei was also observed in dark conditions, where the
slugs sometimes showed an opening level of 3 to 4.
Additionally, opening was observed as a reaction to a
tactile stimulus by carefully touching the slug’s body.
232
E. timida revealed a tendency of broader exposure
of the chloroplasts (parapodia opening levels 3-5)
with higher light irradiances, but in the frame of the
moderate lux values of the natural light spectrum
(and in accordance the reduced photosynthetic active
radiation PAR) through a window in the laboratory
and the short momentous recordings of behavior, a
clear significant correlation between current light
intensity measurements and parapodial position in E.
timida could not be inferred.
The momentary fluorescence values in the PAMmeasurements (F0’), however, increased in strong
correspondence with increasing parapodial opening
level of E. timida individuals which constituted a
significant correlation (p<0.01 in both of the studies,
Spearman rank-order correlation test) (Fig. 6a and b).
While with a low parapodial opening level of 1, the
momentary fluorescence measured in E. timida was
similar to that in T. hopei, the fluorescence values
rose with every higher level of parapodial opening
in E. timida, reflecting the higher exposure of the
imbedded chloroplasts. In contrast, corresponding
yield values, which represent relative values, stayed
constant irrespective of parapodia position (Fig.
7a and b). This can probably be explained by the
increasing measurable maximum fluorescence (Fm)
when parapodia show a higher level of opening. No
remarkable variances in the ground fluorescence were
observed in the measured T. hopei individuals (Fig. 6a)
and yield values were lower than in E. timida (Fig. 7a).
DISCUSSION
In our analyses of phototaxis we observed
phototactic behavior in E. timida with long-term
integration of functional chloroplasts as well as in
T. hopei with short-term chloroplast integration. In
the first phototaxis study with 100 individuals of
E. timida, approximately all individuals had moved
from the dark into the light-exposed area at the end
of each of the four trials. The remaining individuals
were located in the border area under the rim of the
cover where some light was falling in. Thus it can be
concluded that E. timida in general has an automatic
strong and direct phototactic behavior. The second
phototaxis study revealed phototactic behavior also
in T. hopei, but the reaction was less pronounced
than in E. timida. In comparison, individuals of
T. hopei showed a stronger tendency to stay in the
border area under the rim of the cover with only a
slight light incidence or crawl back into this area
while individuals of E. timida showed a stronger
preference of the light-exposed area. With still the
majority of slugs choosing the light-exposed area and
most remaining individuals staying in the border area
with some light incidence, we consider T. hopei as a
phototactic species, but with a gradual difference of
stronger tendency to more shaded areas in contrast
to E. timida. This corresponds to observations of
localities in the sea when collecting the animals.
While E. timida was found mainly on horizontal,
light-exposed rocks, T. hopei was found mainly on
vertical, half-shaded rocks, often even in little holes
in the rock surface. Future experiments with regard to
phototaxis may help to elucidate the distinct behavior
concerning sensitivity in various light regimes.
Fraenkel (1927) wrote that he chose Elysia viridis
for his observations on photomenotaxis out of many
tested opisthobranch species as E. viridis showed the
fastest and clearest reaction. Unfortunately he did not
describe which other species exactly he compared and
in which way. Weaver and Clark (1981) compared the
three sacoglossan species Elysia tuca, Elysia crispata
and Costasiella lilianae (= Costasiella ocellifera
after Clark (1984)) with endosymbiotic chloroplasts
and the two sacoglassan species Oxynoe antillarum
and Berthelinia carribea without endosymbiotic
chloroplasts concerning their photobehavior. They
found that the symbiotic species oriented towards
light while the aposymbiotic species avoided light.
This indicates a possible correlation of chloroplasts’
sequestration and phototaxis. The results of our
phototaxis analyses correspond in so far that both
investigated species are symbiotic and both show
phototactic behavior. As furthermore the phototactic
behavior was stronger in E. timida with long-term
chloroplast retention as in T. hopei with short-term
retention, the question arises, if species with longterm functional chloroplast retention reveal stronger
evolutionary adaptations in relation to endosymbiotic
chloroplasts. The phototactic behavior is more
probably to be regarded as such an evolutionary
adaptation, not as an immediate, direct influence
of the chloroplasts on their host. The finding of our
study that juvenile E. timida already revealed strong
phototaxis before the first integration of chloroplasts
from A. acetabulum supports this assumption.
233
a
b
40
40
340
338
337
30
30
20
20
91
10
Species
Thuridilla hopei
0
N=
112
0
7 8
1
111
2
49
3
31
4
PAR
Elysia timida
243
PAR
89
119
146
10
N=
2
5
Opening degree of parapodia
65
166
53
13
2
1
2
3
4
5
Figure 5:
Current irradiance [PAR: μmol quanta m-2 s-1 ] in relation to opening level of parapodial lobes.
a First trial with 25 Elysia timida and 15 Thuridilla hopei measured 4 times on 2 days respectively in July 2009. b Second trial with 50 E. timida,
measured 4 times on 2 days, respectively, in September 2010. Due to seasonal effects, light incidence in the laboratory reached higher values in
the measurements in July than in September. T. hopei was not observed to open the parapodia more than level 1 (only if touched) and therefore not
included in the second analysis. N displays the number of incidences this parapodial opening level was counted in the behavioral observations. Boxes
represent interquartile ranges divided at median values. Lines are drawn from the top of the box to the largest value within 1.5 interquartile ranges of
the top and the same from the bottom. Symbols display outliers outside this range.
Importance of photosynthesis of the endosymbiotic
chloroplasts as source of nutrients for E. timida was
shown in experiments, in which E. timida was kept
in the dark and thus deprived of the photosynthetic
products of their chloroplast. These individuals had
lower survival rates and stronger size decreases
opposed to those kept in light (Giménez Casalduero
and Muniain, 2008). The need of exposure to light
for the function of the photosynthetic endosymbionts
stands in conflict with potential dangers connected
to exposure, e.g. bigger vulnerability through greater
exposure to predators, waves and currents and
especially damage of photosynthetic endosymbionts
through exposure to irradiances higher than a well
tolerated maximum (Monselise and Rahat, 1980). The
predator problem can be reduced by mechanisms like
producing toxic or irritating secretions and cryptic
234
colorations in sacoglossan sea slugs (Cimino and
Ghiselin, 1998; Marin and Ros, 2004), even if not fully
eliminated. The potential damage of photosynthetic
functions through extreme light intensities still
poses a difficult problem (Jesus et al., 2010). It
seems evident that E. timida has evolved an efficient
protection mechanism against this photodamage
problem with the specialized photobehavior. By
closing the parapodia, E. timida can react directly
to threatening light intensities and form a natural
protection shield for the embedded chloroplast in the
inside of the parapodia. This mechanism enables E.
timida to be located permanently in shallow lightexposed areas and adapt to current light irradiances.
Opening of the parapodia exposes the chloroplasts
to higher irradiation, whereas the closure reduces
light penetration. This specialized photobehavior of
a
b
200
1200
1000
311
43
159
150
800
600
174
176
318
50
Species
p
255
Elysia timida
Thuridilla hopei
0
N=
112
0
7 8
1
111
2
49
3
31
4
2
Ground flu
uorescence
100
Ground flu
uorescence
337
400
200
1
300
28
228
0
N=
5
238
110
211
89
233
59
16
2
1
2
3
4
5
Figure 6:
Ground fluorescence (F0’) in relation to opening level of parapodial lobes.
a First trial with 25 Elysia timida and 15 Thuridilla hopei measured 4 times on 2 days respectively. b Second trial with 50 E. timida, measured 4
times on 2 days, respectively; PAM-settings were increased to high sensitivity (consequently values of momentary fluorescence are higher). N displays
the number of times this parapodial opening level was counted in the behavioral observations. Boxes represent interquartile ranges divided at median
values. Lines are drawn from the top of the box to the largest value within 1.5 interquartile ranges of the top and the same from the bottom. Symbols
display outliers outside this range.
E. timida first described by Rahat and Monselise
(1979) could be confirmed as a general mechanism by
our observations and analyzed in more detail. In our
experiments, we used the emission of the fluorescence
through the parapodia as a factor to indirectly
measure the exposure of the chloroplasts. The closure
of the parapodia unambiguously shows that less light
penetrates the parapodia and therefore protects the
underlying chloroplasts of higher irradiances. With
increasing parapodial opening level the momentary
ground fluorescence values (F0’) in individuals
of E. timida increase in strong correspondence,
which constituted a significant correlation in our
measurements. This reflects the efficiency of the
behavior to expose the inlaying chloroplasts to
light by opening the parapodia and thus enhancing
photosynthetic activity in the integrated chloroplasts.
We assume that the maximum fluorescence (Fm’) rises
also with higher parapodial opening levels, which
equalizes the higher values of ground fluorescence.
As the overall effective yield value of photosynthetic
activity is calculated from (Fm’ – F0’)/Fm’, the effective
yield therefore stayed relatively constant with the
varying parapodial opening levels.
Concerning the specialized photobehavior of E.
timida with light-adapted changing of the position
of the parapodial lobes, the examined behavioral
reactions were very different in the two compared
species. The light-adapted gradual opening of the
parapodia as in E. timida is apparently not present in
T. hopei. Although T. hopei individuals were observed
to actively open their parapodia in reaction to touch or
sometimes in darkness, they did not open them wider
235
a
b
1,0
1,0
221
166
126
138
,8
,8
54
27
205
6
,6
114
,6
21
321
371
380
171
280
221
400
00
195
271
11
53
,4
,4
48
160
Species
,22
140
52
Elysia timida
Thuridilla hopei
0,0
N=
112
0
7
8
1
111
2
49
3
31
4
Yield
Yield
,2
2
0,0
N=
2
5
89
233
59
16
2
1
2
3
4
5
Figure 7:
Yield (Fm’ – F0’/Fm’) in relation to opening level of parapodial lobes.
a) First trial with 25 Elysia timida and 15 Thuridilla hopei measured 4 times on 2 days respectively. b) Second trial with 50 E. timida, measured
4 times on 2 days, respectively; PAM-settings were increased to high sensitivity. N displays the number of times this parapodial opening level was
counted in the behavioral observations. Boxes represent interquartile ranges divided at median values. Lines are drawn from the top of the box to the
largest value within 1.5 interquartile ranges of the top and the same from the bottom. Symbols display outliers outside this range.
than level 1 in the moderate natural light conditions
in the laboratory. The special photobehavior of E.
timida is also related to the characteristic structure of
integrating the chloroplasts into the body. In E. timida,
the embedded chloroplasts can well be seen as a green
area covering the inside of the parapodia while the
outsides of the parapodia and the rest of the body are
full of white pigment with only another small green
stripe on the lower sides of the slug. In contrast T. hopei,
which exhibits a similar arrangement of branched
digestive gland and incorporated chloroplasts, seems
to prevent photosynthesis of chloroplasts by shading
them permanently with the help of the parapodia.
Additionally, the rather dark body coloration may
enhance this shielding of sunlight.
E. timida revealed a tendency of increasing
exposure of the chloroplasts with higher light
irradiances, but in the frame of the moderate lux
236
values of natural light through a window in the
laboratory and the short momentous recordings of
behavior, a clear significant correlation between
current light intensity measurements and parapodial
position in E. timida could not be inferred. The
parapodial position is always connected to the current
active state of the individual. Individuals usually
start to open their parapodia to higher parapodial
opening levels only while sitting in one position for
a while. The opening level 2, which was observed
in the majority of cases in both experiments, is the
characteristic position while crawling. Thus more
observations are necessary for detailed results on the
relation between light conditions and behavior.
It is not explained so far how exactly the specialized
photobehavior of E. timida functions. In general, the
slug’s behavior is in discrepancy anyway: When it
exposes itself to higher irradiances, then chloroplasts
suffer from photodamage and can not be repaired, due
to lack of genomic equipment (Wägele et al., 2010).
When it hides from sunlight, photosynthesis is reduced
and contribution to live maintenance is probably
minor. Jesus et al. (2010) described that E. timida is
capable of combining the behavioral photo-regulation
mechanism (opening/closing the parapodia) with a
functional physiological photo-regulation mechanism
(xanthophyll cycle) increasing their photo-regulation
capacity as a mechanism to keep their maximum
photosynthetic capacity for longer periods. The exact
mechanisms of the specialized photobehavior in E.
timida, however, remain unclear. According to our
observations until now, this specialized photobehavior
is rather specific for E. timida. It represents a highly
specialized evolutionary adaptation in relation to
long-term retention of chloroplasts with efficient
exposure of endosymbiotic chloroplast for high
photosynthetic benefit as well as efficient protection
of endosymbiotic chloroplasts from photo-damage,
enabling functionality of chloroplast endosymbiosis
in E. timida for one of the most extended durations
known so far.
ACKNOWLEDGEMENTS
The project was partly supported by the European
Community with an ASSEMBLE grant agreement
no. 227799 to VS and partly by the German Science
Foundation (Wa618/12) to HW. Furthermore, we
thank the Observatoire Océanologique Banyuls sur
mer for providing laboratory facilities and assistance
and also Susanne Gunkel for assistance in breeding
juvenile E. timida.
REFERENCES
Evertsen J, Burghardt I, Johnsen G, Wägele H (2007).
Retention of functional chloroplasts in
some sacoglossans from the Indo-Pacific and Mediterranean.
Cimino G, Ghiselin MT (1998). Chemical defence and
evolution in Sacoglossa (Mollusca: Gastropoda:
Opisthobranchia). Chemoecology, 8: 51-60.
Clark KB (1984). New records and synonymies of Bermuda
Opisthobranchs (Gastropoda). The Nautilus, 98: 85-97.
Fraenkel G (1927). Über Photomenotaxis bei Elysia viridis
Mont.. Zeitschrift für vergleichende Physiologie, 6:
385-401.
Giménez Casalduero F, Muniain C (2008). The role of
kleptoplasts in the survival rates of Elysia timida
(Risso, 1818): (Sacoglossa: Opisthobranchia) during
periods of food shortage. Journal of Experimental
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Händeler K, Grzymbowski Y, Krug PJ, Wägele H (2009).
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functional xanthophyll cycle enhance photo-regulation
mechanism in the solar-powered sea slug Elysia timida
(Risso 1818). Journal of Experimental Marine Biology
and Ecology, 395: 98-105.
Marin A, Ros J (1989). The chloroplast-animal association
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Marin A, Ros J (1992). Dynamics of a plant-herbivore
relationship: the photosynthetic ascoglossan Elysia
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Marin A, Ros J (1993). Ultrastructural and ecological
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the sacoglossan gastropod Elysia timida. Journal of
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Monselise EBI, Rahat M (1980). Photobiology of Elysia
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Rahat M, Monselise EBI (1979). Photobiology of
the chloroplast-hosting mollusc Elysia timida
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79: 225-233.
Wägele H, Deutsch O, Händeler K, Martin R, Schmitt V,
Christa G, Pinzger B, Gould SB, Dagan T, KlussmannKolb A, Martin W (2010). Transcriptomic evidence that
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longevity of aquired plastids in the photosynthetic slugs
Elysia timida and Plakobranchus ocellatus does not
entail lateral transfer of algal nuclear genes. Molecular
Biology and Evolution, 28: 699-706.
Wägele H, Johnsen G (2001). Observations on the
histology and photosynthetic performance of “solarpowered” opisthobranchs (Mollusca, Gastropoda,
Opisthobranchia) containing symbiotic chloroplasts or
zooxanthellae. Organisms Diversity and Evolution, 1:
193-210.
Weaver S, Clark KB (1981). Light intensity and color
preferences in five ascoglossan (=sacoglossan) molluscs
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and Freshwater Behavior and Physiology, 7: 297-306.
238
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Thalassas - Universidade de Vigo

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