Contribution to the knowledge of freshwater Gastrotricha from

freshwater gastrotricha from denmark
79
Contribution to the knowledge of freshwater Gastrotricha from
Denmark
PAOLO GRILLI, REINHARDT MØBJERG KRISTENSEN & MARIA BALSAMO
Steenstrupia
Grilli, P., R. M. Kristensen & M. Balsamo. Contribution to the knowledge of freshwater Gastrotricha
from Denmark. – Steenstrupia 32 (1): 79–92. Copenhagen, Denmark. February 2010. ISSN 03752909.
Faunistic knowledge of European Gastrotricha is very heterogeneous. The marine species have been
the subject of numerous investigations, whereas the freshwater species have been studied only in a
few countries or regions. In Denmark only 2 freshwater and 14 marine species of Chaetonotida have
been reported, and a new species, Heterolepidoderma caudosquamatum, has recently been described
from brackish waters. An investigation aimed to improve the knowledge of Gastrotricha Chaetonotida
of Danish inland waters was carried out at the island of Seeland (Copenhagen-area). Five biotopes
with different ecological conditions were sampled and 26 species were found, belonging to the genera
Aspidiophorus, Chaetonotus, Haltidytes, Heterolepidoderma, Ichthydium and Polymerurus. All these
species, except for Ichthydium podura (Müller, 1773), are new records for Denmark. Both cosmopolitan species and rare species have been found. The most species-rich fauna (13 species) was found in
the site with the most abundant aquatic vegetation, whereas no more than 4 species were present in
the dystrophic sites. Taking into account the high number of freshwater biotopes present in Denmark,
further investigations on the gastrotrich fauna will certainly increase the number of species records.
Keywords: freshwater meiofauna, Gastrotricha, Chaetonotida, Danish fauna, ecology
Paolo Grilli and Maria Balsamo: Dipartimento di Scienze dell'Uomo, dell'Ambiente e della Natura,
Università di Urbino 'Carlo Bo', Via Oddi 21, I-61029 Urbino, Italy. E-mail: [email protected]
Reinhardt Møbjerg Kristensen, Zoological Museum, Natural History Museum of Denmark, University
of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark. E-mail: rmkristensen@snm.
ku.dk
INTRODUCTION
The phylum Gastrotricha consists of about 750
species of micrometazoans (80-1500 µm body
length) living in interstitial, epibenthic and
periphytic habitats, through which they move
actively by means of an extended ventral ciliature, which gives the name to the phylum (from
the ancient Greek gastér = stomach, thrix =
cilium). Gastrotricha are divided into two orders,
Macrodasyida and Chaetonotida, distinct from
great differences in morphological and biological
characteristics (Ruppert 1991). Macrodasyida
are the most primitive order and group about
280 strap-shaped species that colonize interstitial
marine or brackish habitats. Only two species,
Redudasys fornerisae Kisielewski, 1987 and
Marinellina flagellata Ruttner-Kolisko, 1955 are
known to live in freshwater habitats. The order
Chaetonotida is numerically larger, with about
Steenstrupia 32 (1): 79–92.
470 tenpin-shaped species mostly inhabiting
freshwater environments such as epibenthic, periphytic or interstitial biotopes (Ricci & Balsamo
2000). However, three families (Muselliferidae,
Neodasyidae, Xenotrichulidae) as well as a number of Chaetonotidae colonize marine or brackish, mostly interstitial habitats.
The phylum Gastrotricha has a cosmopolitan
distribution, and is an important component of
benthos and periphyton in freshwater environments, with densities up to 100.000 individuals
per m2 (Nesteruk 1996 a, b). However, because
of their microscopic size, the fragility of the body
and the consequent difficulty of study, these animals are still insufficiently known.
The current taxonomy of Gastrotricha is
mainly based on morphological characters, but
many species show a high degree of intraspecific
80
p. grilli, r. m. kristensen & m. balsamo
Fig. 1. Geographical location of the collecting stations: 1. Zoological Museum, Natural History Museum of Denmark (N.H.M.);
2. Fælledparken; 3, 4. Eremitagesletten; 5. Utterslev Mose.
variability that makes identification difficult. A
careful assessment of the literature has recently
been carried out for compiling an on-line global
database of the reliable freshwater Gastrotricha
species, with information on their taxonomic
status and geographic distribution (Balsamo et
al. 2009).
The faunistic knowledge of European freshwater Gastrotricha is very heterogeneous. Numerous investigations have been carried out in
Italy, France, Germany, Poland and Great Britain,
whereas the information on other countries is still
very poor (Balsamo et al. 2008). In Denmark,
only 2 freshwater species (Chaetonotus larus
(Müller, 1773) and Ichthydium podura (Müller,
1773)) and 14 marine species of Chaetonotida
(Aspidiophorus mediterraneus Remane, 1927;
Chaetonotus atrox Wilke, 1954; C. somniculo­
sus Mock, 1979; Diuronotus rupperti Todaro,
Balsamo & Kristensen, 2005; Draculiciteria
tesselata (Renaud-Mornant, 1968); Halicha­
etonotus aculifer (Gerlach, 1953); H. mari­
nus (Giard, 1904); H. pleuracanthus (Remane,
1926); H
­ eterolepidoderma grandiculum Mock,
1979; H. marinum Remane, 1926; Heteroxenot­
richula affinis (Remane, 1934); H. squa­mosa
Wilke, 1954; Xenotrichula inter­media R
­ emane,
1934; X. velox Remane, 1927) have been reported
(Müller 1773, Mock 1979, Todaro et al. 2005,
http://data.gbif.org). An additional species, Het­
erolepidoderma caudosquamatum Grilli, Kristensen & Balsamo, 2009 was recently described
from a brackish-water pond in the Copenhagen’s
docklands area (Grilli et al. 2009).
In order to improve the knowledge of Danish freshwater Gastrotricha, a faunistic study
has been carried out on the island of Seeland
(Copenhagen-area).
MATERIAL AND METHODS
The study was carried out in May-June 2008
focusing on four permanent and one temporary
freshwater biotopes characterized by different ecological conditions. Three of these were
characterised by rooted hydrophytes (e.g. Cal­
81
freshwater gastrotricha from denmark
Table 1. Georeferential location and main ecological characteristics of each collecting station.
Station Station name
no.
1
2
3
4
5
N.H.M. pond
Fælledparken
Eremitagesletten
Eremitagesletten
Utterslev Mose
Geographical coordinates Pond type
55°42.205' N, 12°33.371' E
55°42.204' N, 12°33.651' E
55°47.385' N, 12°35.074' E
55°47.442' N, 12°34.309' E
55°43.157' N, 12°30.970' E
Water
trophism
permanent mesotrophic
permanent dystrophic
temporal mesotrophic
permanent dystrophic
permanent eutrophic
Rooted/floating
vegetation
moderate
poor
abundant
poor
abundant
litriche sp., Ceratophyllum sp., Phragmites
australis) and abundant floating vegetation (e.g.
Lemma minor, Azolla filiculoides). The others
were characterised by dystrophic conditions.
The location and some ecological characteristics
of each collecting station are reported in Fig. 1
and Table 1.
Several samples were collected from different
points of each pond (Stations 1-5), at a distance
of 1-1.5 m from the shoreline, and at a depth
of 0.20-1.50 m, using a nylon net with meshes
of 30 µm (Giere 2009). The aquatic vegetation
was washed and pressed into the same net in
order to collect the periphytic species. The water
from each sampling point was repeatedly filtered
through the same net for the study of the planktonic species. The material collected was poured
into sealed jars and transported to the laboratory.
The study of animals started after 24 hours, period necessary to the sedimentation of suspended
material, and then continued daily over a period
of 1-2 weeks. Small quantities of the superficial
layer of sediment were analyzed under a stereomicroscope, and gastrotrichs were isolated and
then studied under a Nomarski interference contrast microscope. In most cases permanent slides
of specimens were made in order to allow more
accurate observations of diagnostic characteristics as well as to file them in the Authors’ collection. Cluster analysis, based on the Bray-Curtis
similarity was used to evaluate the differences
on taxonomic composition of the sampling sites
(presence/absence transformation). The analyses
were performed using the Primer® v.5 software
package (Clarke & Gorley 2001).
RESULTS
Abbreviations: f, furca; h, head; n, neck; L,
length; TL, total length; ph, pharynx; sp, spine/s;
sc, scale/s; tr, trunk; w, width.
TL 170–190 μm; f L 20–24 μm; ph L 72–76 μm;
h w 30–34 μm; tr w 31–48 μm; tr sc L 5 μm; tr
sc w 3 μm.
A total of 92 individuals belonging to 26 species
of the genera Aspidiophorus, Chaetonotus, Halti­
dytes, Heterolepidoderma, Ichthydium and Poly­
merurus were collected and identified (Table 2).
All the species, except for Ichthydium podura,
are first records for Denmark although ��������
the specific affiliation of one of them (Chaetonotus cf.
pratensis Schwank, 1990) has to be confirmed.
Chaetonotus was the most species-rich genus (20
species), followed by Aspidiophorus (2 species),
and Haltidytes, Heterolepidoderma, Ichthydium,
Polymerurus (1 species each).
TAXONOMY
Order Chaetonotida Remane, 1925 [Rao &
Clausen, 1970]
Suborder Paucitubulatina d’Hondt, 1971
Family Chaetonotidae Gosse, 1864
Subfamily Chaetonotinae Kisielewski, 1991
Aspidiophorus Voigt, 1904
Aspidiophorus paradoxus (Voigt, 1902)
Figs. 2A, 3F
Material examined:
6 specimens; Stations 2, 3, 5.
82
p. grilli, r. m. kristensen & m. balsamo
freshwater gastrotricha from denmark
The morphometric parameters of the specimens corresponded to the literature data for this
species, even if they were close to the lower limits
reported. All the specimens found were sexually
mature with a very large egg. 17–25 columns of
40–45 pedunculate rhombic scales, one parafurcal spine (L 4–6 μm) at the end of each lateral
scale column. Cosmopolitan species reported
from Europe (Bulgaria, France, Germany, Great
Britain, Hungary, Italy, Poland, Romania, Russia, Switzerland), Japan and USA.
Aspidiophorus squamulosus (Roszczak, 1936)
83
kephalion and four tufts of cephalic cilia; 13–16
columns of 25–27 semicircular scales with sharp
simple spines. Two parafurcal long spines (8–10
μm) at each furcal side. Four animals found were
sexually mature with one or two large eggs. Typical periphytic species, common in Central-Eastern Europe (Austria, Germany, Great Britain,
Hungary, Italy, Poland, Romania, Russia), and
reported from Canada, USA, India and Malaysia
(Singapore).
Chaetonotus (C.) disjunctus Greuter, 1917
Figs. 2G, 3L
Material examined:
8 specimens; Stations 3, 5.
Material examined:
2 specimens; Station 3.
TL 160–180 μm; f L 13–14 μm; tr sc L 3 μm; tr
sc w 5–6 μm.
Medium-sized species with relatively short
furca. Five-lobed head, with dorsally extended
kephalion, pleuria and hypostomium. 40–42
rhombic scales arranged into 15 columns. 3
spines (L 7–10 μm) at the base of each furcal
appendage. All the specimens were adults in
parthenogenetic phase. The dimensions measured were in agreement with those given in the
literature. This species is reported only from Italy
and Poland.
Chaetonotus (Chaetonotus) Ehrenberg, 1830
[Kisielewski, 1997]
TL 134–170 μm; f L 16–20 μm; ph L 40–43 μm;
h w 21–23 μm; n w 19–22 μm; tr w 31–35 μm;
tr sp L 11–15 μm.
Dimensions of the specimens collected are
close to the lower limits reported for the species.
Stocky body, five-lobed head and a relatively
short furca. Large kephalion, two pairs of pleuria, no hypostomion; 9–13 alternate columns of
21–25 trilobate, spined scales spaced apart from
each other. Spines are simple, very curved, short
and thick. A pair of spines (L 10 μm) at the base
of each furcal appendage. Two pairs of dorsal
bristles. Species reported from mesotrophic and
eutrophic habitats of several European countries
(France, Germany, Great Britain, Italy, Poland,
Romania, Russia, Spain, Switzerland) and also
in Japan.
Chaetonotus (C.) brevispinosus Zelinka, 1889
Chaetonotus (C.) elegans Konsuloff, 1921
Chaetonotus Ehrenberg, 1830
Material examined:
6 specimens; Stations 3, 5.
TL 105–120 μm; f L 18–20 μm; ph L 24–25 μm;
h w 23–30 μm; n w 16 μm; tr w 35–39 μm; h sp
L 3–4 μm; tr sp L 6–7 μm.
The dimensions of the specimens collected
fit with the data reported for the species. Slender body of small size. Five-lobed head with
Fig. 3A
Material examined:
11 specimens; Stations 3, 5.
TL 150–165 μm; f L 17–22 μm; ph L 35–40 μm;
h w 30 μm; n w 29 μm; tr w 37 μm; tr sc L 8–10
μm; tr sp L 5–7 μm.
All specimens observed were in parthenogenetic phase. Slender body, dimensions within
Fig. 2. Schematic drawings of some Chaetonotida freshwater species found during this study. A. Aspidiophorus paradoxus.
B. Chaetonotus (Z.) bisacer. C. Chaetonotus (P.) brachyurus, dorsal and ventral view. D. Chaetonotus (C.) polyspinosus. E.
Chaetonotus (C.) tricuspidatus. F. Haltidytes crassus, dorsal and ventral view. G. Chaetonotus (C.) disjunctus. H. Polymerurus
nodicaudus. – Scale bars in μm. Modified from Balsamo (1983) and Schwank (1990).
84
p. grilli, r. m. kristensen & m. balsamo
the values reported for the species. Five-lobed
head with developed kephalion and four tufts of
short cilia. A pair of bristles on the neck, 13–17
columns of 25–30 trilobate scales with short,
simple spines increasing in length from the head
to the caudal end. Two longer spines (10 μm) at
the end of each lateral row of spines. Species
reported from Bulgaria, France, Germany, Hungary and Romania.
Chaetonotus (C.) greuteri Remane, 1917
Fig. 3H
Material examined:
2 specimens; Station 2.
TL 130–150 μm; f L 20–25 μm; ph L 40–45 μm;
h w 30–32 μm; tr w 30–32 μm; h sp L 6–8 μm;
tr sp L 17–18 μm.
The morphology and the dimensions of the
animals collected corresponded to the data of
the literature. Large, three-lobed head with an
extended kephalion and two tufts of long cilia;
12–15 columns of 30–32 subtriangular scales
with very thin simple spines increasing in length
towards the caudal end. No spines in the intrafurcal area. Species reported from Germany, Great
Britain, Poland, Romania and Switzerland.
Chaetonotus (C.) heterospinosus Balsamo,
1978
Material examined:
1 specimen; Station 3.
TL 145 μm; f L 24 μm; ph L 46 μm; h w 31 μm;
n w 24 μm; tr w 43 μm; h sp L 4 μm; tr sp L 19
μm.
Species known for a great intraspecific variability of the cuticular scaling. The only specimen collected corresponded to morphotype A
described by Balsamo (1980), and characterized
by 6 dorsal terminal spines with an accessory
point. It is a common Italian species reported
also from France, Russia and in Korea, from
periphytic and interstitial habitats.
Chaetonotus (C.) hystrix Metschnikoff,1865
Material examined:
3 specimens; Station 1.
TL 100 μm; f L 10–12 μm; ph L 30–35 μm; h w
18–20 μm; n w 14–18 μm; tr w 22–26 μm; tr sp
L 13–20 μm.
Slender body, three-lobed head and a relatively
short furca. Large kephalion, two pairs of pleuria;
9 columns of 15 three-lobed scales. Spines were
thick and bent. The dimensions of the specimens
studied are within the values known for the species. C. (C.) hystrix is a cosmopolitan, epibenthic
and periphytic species, reported also from the
interstitial habitat. It is common in Europe (Belgium, Bulgaria, France, Great Britain, Hungary,
Italy, Poland, Romania, Russia) and also in Israel,
Japan and South America (Brazil, Paraguay).
Chaetonotus (C.) laroides Marcolongo, 1910
Fig. 3I
Material examined:
2 specimens; Station 5.
TL 217 μm; f L 28 μm; h w 40 μm; tr w 72 μm;
tr sp L 15–20 μm; h sp L 10–12 μm.
The dimensions of the specimens collected
fall in the range reported in the literature for the
species. 13–17 columns of 28–32 semielliptic,
relatively large (4–5 μm), juxtaposed scales with
a simple spine. At the dorsal body end many
small scales with a short spine process. Both animals found were sexually mature with one large
egg. Species reported only from Italy, Germany
and Romania.
Chaetonotus (C.) macrochaetus Zelinka, 1889
Material examined:
3 specimens; Stations 1, 2.
TL 131–140 μm; f L 14–17 μm; ph L 25–28 μm;
h w 20–22 μm; n w 18–20 μm; tr w 23–24 μm;
tr sp L 11–17 μm.
Stocky body, five-lobed head, large kephalion,
two pairs of pleuria and a relatively short furca;
8-10 columns of 14–17 three-lobed scales with
a spine provided with an accessory point. Spine
length increased from 6 μm on the head to 17 μm
in the caudal region. Typical of the periphyton
in mesotrophic environments, but also reported
from the interstitial. Recorded from Centraleastern Europe (Austria, Bulgaria, Estonia, Germany, Great Britain, Hungary, Italy, Poland,
freshwater gastrotricha from denmark
85
Fig. 3. Microphotographs of some Chaetonotida freshwater species found during this study. – A. Chaetonotus (C.) elegans. – B.
Chaetonotus (Z.) bisacer. B1, B2. Detail of the dorsal scales. – C. Chaetonotus (P.) macrolepidotus ophiogaster. C1. detail of
the dorsal scales. – D. Chaetonotus (C.) sphagnophilus. – E. Haltidytes crassus. – F. Aspidiophorus paradoxus, dorsal view.
F1. Ventral view: a mature egg is visible. – G. Chaetonotus (C.) polyspinosus. – H. Chaetonotus (C.) greuteri. – I. Chaetonotus
(C.) laroides. – J. Ichthydium podura. – K. Polymerurus nodicaudus, ventral view. Note the cephalic plates and the pharynx.
K1. Total view. – L. Chaetonotus (C.) disjunctus.
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p. grilli, r. m. kristensen & m. balsamo
Table 2. Taxonomic list and distribution of the freshwater species of Gastrotricha currently known in Denmark. Asterisks (*)
mark previously reported species.
Phylum
Order
Suborder
Family
Subfamily
Genus
Genus
Subgenus
Subgenus
Subgenus
Subgenus
Genus
Genus
Genus
Family
Genus
Gastrotricha Metschnikoff, 1865
Chaetonotida
Paucitubulatina
Chaetonotidae
Chaetonotinae
Aspidiophorus
Aspidiophorus
Aspidiophorus
Chaetonotus
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Chaetonotus)
Chaetonotus (Captochaetus)
Chaetonotus (Captochaetus)
Chaetonotus (Primochaetus)
Chaetonotus (Primochaetus)
Chaetonotus (Primochaetus)
Chaetonotus (Primochaetus)
Chaetonotus (Zonochaeta)
Chaetonotus (Zonochaeta)
Heterolepidoderma
Heterolepidoderma
Ichthydium
Ichthydium
Polymerurus
Polymerurus
Dasydytidae
Haltidytes
Remane, 1925 [Rao & Clausen, 1970]
d’Hondt, 1971
Gosse, 1864
Kisielewski, 1991
Voigt, 1904
paradoxus Voigt, 1902
squamulosus (Roszczak, 1936)
Ehrenberg, 1830
Ehrenberg, 1830 [Kisielewski, 1997]
brevispinosus Zelinka, 1889
disjunctus Greuter, 1917
elegans Konsuloff, 1921
greuteri Remane, 1917
heterospinosus Balsamo, 1978
hystrix Metschnikoff,1865
laroides Marcolongo, 1910
larus (Müller, 1773) (*)
macrochaetus Zelinka, 1889
maximus Ehrenberg, 1838
minimus Marcolongo, 1910
multispinosus Grünspan, 1908
persetosus Zelinka, 1889
polyspinosus Greuter, 1917
cf. pratensis Schwank, 1990
sphagnophilus Kisielewski, 1981
Kisielewski, 1997
tricuspidatus Schwank, 1990
Kisielewski, 1997
brachyurus Balsamo, 1980
macrolepidotus macrolepidotus Greuter, 1917
macrolepidotus ophiogaster Remane, 1927
Remane, 1927
bisacer Greuter, 1917
Remane, 1927
lamellatum Balsamo & Fregni, 1995
Ehrenberg, 1830
podura (Müller, 1773) (*)
Remane, 1927
nodicaudus (Voigt, 1901)
Daday, 1905
Remane, 1936
Haltidytes crassus (Greuter, 1917)
Sampling stations
1 2 3 4 5
- ● ● - ●
- - ● - ●
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-
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-
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-
-
-
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-
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-
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-
-
-
-
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-
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freshwater gastrotricha from denmark
Romania, Russia, Switzerland) USA, Canada,
Brazil and Israel.
Chaetonotus (C.) maximus Ehrenberg, 1838
Material examined:
1 specimen; Station 3.
TL 130 μm; f L 16 μm; ph L 61 μm; h w 31 μm;
n w 28 μm; tr w 44 μm; tr sp L 16 μm.
The morphology and the dimensions of the
single animal collected correspond to the literature data. Slender body, five-lobed head, two
pairs of pleuria and a relatively short furca; 15
columns of 28 elliptic scales with a simple spine;
3 parafurcal spines (L 18 μm) per side. Two terminal, keeled plates (L 9 μm) at the ventral body
end. Cosmopolitan, epibenthic and periphytic
species, found also in the interstitial habitat. C.
(C.) maximus is reported from many European
countries (Austria, Belgium, Bulgaria, Czech
Republic, Estonia, France, Germany, Great Britain, Hungary, Ireland, Italy, Poland, Romania,
Russia, Spain, Switzerland), and also from North
America, Africa, Japan and Australia.
Chaetonotus (C.) minimus Marcolongo, 1910
Material examined:
3 specimens; Station 5.
TL 100–105 μm; f L 10–12 μm; ph L 22–25 μm;
h w 18 μm; n w 18 μm; tr w 20–24 μm.
Very small species, five-lobed head, developed
kephalion and four tufts of cilia. 9–13 alternate
columns of 38–40 suboval, juxtaposed scales,
which cover the body up to the base of the furca
appendages. The dimensions of the specimens
collected agree with those reported for the species. Reported only from Italy and Germany.
Chaetonotus (C.) multispinosus Grünspan,
1908
Material examined:
4 specimens; Station 5.
TL 95–100 μm; f L 9–11 μm; ph L 33–38 μm; h
w 30 μm; tr w 33–39 μm.
87
Slender body, five-lobed head, four tufts of
cilia. 16��������������������������������������
–19 alternate columns of 35–38 semielliptic, juxtaposed scales with a very short spine.
Short furca. The morphology and the dimension
of the animals collected correspond to the data reported in the literature for this species. Reported
from Austria, France, Germany, Hungary, Italy,
Poland, Romania, Russia and Japan.
Chaetonotus (C.) persetosus Zelinka, 1889
Material examined:
1 specimen; Station 1.
TL 100 μm; f L 13 μm; ph L 24 μm; h w 16 μm;
n w 14 μm; tr w 22 μm; tr sc L 5 μm; tr sp L 16
μm.
Small species, five-lobed head; 9 columns of
18 trilobate scales with a thick spine provided
with an accessory point. Spines increasing in
length from the head to the caudal appendage.
Two terminal, elliptic, keeled plates (L 8.3 μm; w
2.3 μm) at the ventral body end. Species of peri­
phytic and interstitial habitats. Widely distributed in central-eastern Europe (Bulgaria, France,
Germany, Great Britain, Italy, Poland, Romania,
Russia), Japan, Korea and Brazil.
Chaetonotus (C.) polyspinosus Greuter, 1917
Figs. 2D, 3G
Material examined:
6 specimens; Station 5.
TL 315–327 μm; f L 19–22 μm; ph L 85–91 μm;
h w 41–44 μm; n w 40 μm; tr w 56–60 μm; tr sc
L 4–5 μm.
Specimens of relatively large dimensions and
slender body; 25 alternate columns of 58–62
subtriangular scales with a thin and simple spine.
The last 3 pairs of lateral spines and 4 terminal
dorsal spines were appreciably longer (L 10–12
μm). The dimensions of the specimens collected
are close to the lower limits described for the
species. Typical of mesotrophic and eutrophic
environments, present also in the interstitial. Reported from many European countries (France,
Great Britain, Italy, Poland, Romania, Russia,
Switzerland) and from Canada, Brazil, Israel
and Korea.
88
p. grilli, r. m. kristensen & m. balsamo
Chaetonotus (C.) cf. pratensis Schwank, 1990
Material examined:
1 specimen; Station 3.
TL 140 μm; f L 18 μm; ph L 34 μm; h w 25 μm;
tr w 29 μm; tr sc L 14 μm; h sc L 6 μm.
Slender and small body. Five-lobed head with
four tufts of cilia; 13 columns of 27 rhombic
scales (3.6 x 3.4 μm) with a simple spine. The
only animal collected was partially contracted,
so that the observation could not be completed.
The morphology and dimensions of the specimen
corresponded to the original data for the species
(Schwank 1990), but this report needs to be
confirmed. Reported only from Germany.
Chaetonotus (C.) sphagnophilus Kisielewski,
1981
Fig. 3D
Material examined:
1 specimen; Station 3.
TL 147 μm; f L 15 μm; ph L 28 μm; h w 26 μm;
tr w 28 μm; tr sc L 10 μm, tr sp L 13 μm, h sp
L 4 μm.
Slender body, three-lobed head with four tufts
of cilia; 7 dorsal columns and 6 ventrolateral
columns per side, of 30 three-lobed scales with
a relatively short spine. Scales covered the body
up to the base of the furca. The specimen was
sexually mature with a very large egg. Reported
from France, Italy, Poland and Russia.
Chaetonotus (Captochaetus) Kisielewski,
1997
Chaetonotus (C.) tricuspidatus Schwank, 1990
Fig. 2E
Material examined:
3 specimens; Station 1.
TL 270–275 μm; f L 38 μm; ph L 70–76 μm; h
w 42 μm tr w 67–73 μm; h sp L 7 μm; tr sp L
16 μm.
Stout body. Five-lobed head with four tufts
of cilia; 10 columns of 32 trilobate scales with
a thick and short simple spine. Three spines on
each furcal appendage, two of which parafurcal.
Reported only from Germany.
Chaetonotus (Primochaetus) Kisielewski,
1997
Chaetonotus (P.) brachyurus Balsamo, 1980
Fig. 2C
Material examined:
1 specimen; Station 2.
TL 140 μm; f L 6 μm; ph L 35 μm; h w 31 μm;
n w 28 μm; tr w 51 μm; tr sc L 10 μm; tr sp L
22 μm.
Stout body, five-lobed head, four tufts of cilia,
extended kephalion; 7 columns of 15 trapezoidal
scales (tr sc 10 x 10 μm) with a long simple
spine increasing in length from the head (8 μm)
to the caudal appendage (22 μm). Very short
furcal appendages without adhesive tubes. Two
instead of four parafurcal spines were observed
on each furcal appendage. The specimen found
was sexually mature with one large egg. Only
reported from Italy.
Chaetonotus (P.) macrolepidotus macro­
lepidotus Greuter, 1917
Material examined:
2 specimens; Station 3.
TL 150 μm; f L 20–25 μm; ph L 38 μm; h w 25–26
μm; tr w 41 μm; tr sc L 11–14 μm.
Stout body, five-lobed head and four tufts of
cilia. Short and stubby pharynx. 4 dorsal columns
and 1 ventrolateral column per side of 15 elliptic
scales with a simple spine increasing in length
caudally. In the dorsal caudal area the scales
were very small, with very short spines. Ventral,
interciliary area 21 μm wide. Species reported
only from Great Britain, Poland, Romania, Russia and Switzerland.
Chaetonotus (P.) macrolepidotus ophiogaster
Remane, 1927
Fig. 3C
Material examined:
5 specimens; Station 3.
TL 100–110 μm; f L 12–20 μm; ph L 32–35 μm;
h w 23–24 μm; n w 19–22 μm; tr w 25–29 μm;
tr sc L 9.6 μm.
freshwater gastrotricha from denmark
89
Fig. 4. Cluster analysis based on Bray-Curtis Similarity according to presence/absence of species by location.
Slender body, five-lobed head with four tufts
of cilia. Pharynx with a posterior bulb. Four
dorsal columns and 2 ventrolateral columns per
side of 21 round scales with a very short spined
process. A dorsal series of 6 very long spines (L
7–9 μm) on the trunk. Two long lateral spines
per side (L 10–12 μm), the one inserted at the
same level of the dorsal ones, the other at the
base of the furcal tube (L 12–15 μm). Reported
from Germany, Great Britain, Poland, Romania,
Russia, Switzerland and Canada.
an accessory point (L 30–33 μm). On each trunk
side a posterior lateral spine (L 10–12 μm) and
a parafurcal spine (L 40–45 μm) at a distance of
20 μm from each other. Cosmopolitan species
reported from Europe (Germany, Great Britain,
Italy, Poland, Romania, Russia, Switzerland),
Asia (Japan, Korea and India), North and South
America (Canada, U.S., Brazil and Argentina).
Heterolepidoderma Remane, 1927
Chaetonotus (Zonochaeta) Remane, 1927
Heterolepidoderma lamellatum Balsamo &
Fregni, 1995
Chaetonotus (Z.) bisacer Greuter, 1917
Material examined:
1 specimen; Station 1.
Figs. 2B, 3B
Material examined:
6 specimens; Stations 3, 5.
TL 160 μm; f L 19 μm; ph L 35–43 μm; h w 32–35
μm; n w 23–29 μm; tr w 32–36 μm.
Slender body, five-lobed head, well-developed kephalion. Pharynx with a posterior bulb.
Eleven columns of 35 scales with a short spined
process. A dorsal series of 11 long spines with
TL 105 μm; f L 12 μm; ph L 26 μm; h w 22 μm; n
w 18 μm; tr w 30 μm; tr sc L 4 μm; v pl L 5 μm.
The dimensions of the specimen collected are
close to the lower limits reported for the species.
Slender body of very small size. Five-lobed head
with kephalion, pleuria and a sub-rectangular
hypostomion. Four tufts of cephalic cilia. 17–23
columns (13–17 dorsal), each composed of 25–
30 suboval, keeled scales. The columns joined
90
p. grilli, r. m. kristensen & m. balsamo
together on the neck and at the posterior body
end. Two pairs of dorsal sensory bristles. One
ventrolateral column of scales for each body side,
provided with a lamellar expansion (hydrophoil
scales). Two ventral ciliary bands. In the interciliary area 5 columns of small, elliptical keeled
scales with a spiny process, and two oval, keeled,
terminal plates. Interstitial species reported only
from Italy.
Ichthydium Ehrenberg, 1830
Germany, Great Britain, Hungary, Italy, Poland,
Romania, Russia, Switzerland, Ukraine), Asia
(India, Israel, Japan, Korea), North and South
America, Australia.
Family Dasydytidae Daday, 1905
Haltidytes Remane, 1936
Haltidytes crassus (Greuter, 1917)
Figs. 2F, 3E
Ichthydium podura (Müller, 1773)
Material examined:
2 specimens; Station 5.
Material examined:
8 specimens; Stations 3, 5.
TL 110–120 μm; ph L 30–35 μm; h w 20–25 μm;
n w 15–18 μm; tr w 35–40 μm.
The morphology and the dimensions of
the animals collected correspond to the data
presented in the literature. The head bears an
extended ciliature. Five pairs of long peculiar
spines (L 100–110 μm) inserted dorsolaterally
but extending on the dorsal body side, and 3
pairs of long ventral spines of which the last pair
was the longest one (L 140–150 μm). Planktonic
species, known in Italy, Romania, Russia, Switzerland, Canada and Argentina.
Fig. 3J
TL 80–95 μm; ph L 20–23 μm; f L 10–12 μm.
The size of the specimens collected agree
with that reported in the literature. Cosmopolitan
species of interstitial and periphytic habitats,
already known for Denmark and many other
European countries (Austria, Bulgaria, France,
Germany, Great Britain, Hungary, Italy, Norway,
Poland, Romania, Russia, Switzerland), Africa
(Madagascar, Sudan), Japan, North and South
America.
Polymerurus Remane, 1927
DISCUSSION
Polymerurus nodicaudus (Voigt, 1901)
The faunistic composition of the ponds investigated showed few overlaps. The species collected
in two or more biotopes were Aspidiophorus par­
adoxus, A. squamulosus, Chaetonotus bisacer, C.
brevispinosus, C. elegans, C. macrochaetus and
Ichthydium podura, while all the other species
were found in a single pond. Both cosmopolitan
species (i.e. Chaetonotus hystrix, C. maximus),
and rare species (i.e. the semiplanktonic Halti­
dytes crassus) have been found.
It is worth noting that some species found
during this study have a very limited geographic
distribution, like Aspidiophorus squamulosus, a
species known until now only in Italy and Poland; Chaetonotus minimus, known in Italy and
Germany; Chaetonotus tricuspidatus, known in
Germany, and Chaetonotus brachyurus and Het­
Figs. 2H, 3K
Material examined:
3 specimens; Station 5.
TL 262–278 μm; f L 71 μm; ph L 45–48 μm;
h w 34 μm; n w 33 μm; tr w 34.5 μm; tr sp L
15–18 μm.
Slender body, three-lobed head with a welldeveloped kephalion. Twenty columns of 56
polygonal scales with a short spined process. All
the observed specimens were in parthenogenetic
phase and their body length was shorter than that
described in the literature (262–278 vs 300–550
μm). Species typical for the periphyton but found
twice in the interstitial environment. Cosmopolitan and reported from Europe (Bulgaria, France,
freshwater gastrotricha from denmark
erolepidoderma lamellatum, both known only
in Italy. If confirmed, the record of Chaetonotus
pratensis could contribute to widen the biogeographical distribution of the species, known only
in Germany so far.
The Stations 1, and especially 3 and 5, where
the presence of abundant rooted hydrophytes
and floating vegetation were evident, showed the
richest gastrotrich fauna (5, 13 and 12 species
respectively). On the contrary, dystrophic ponds
(Stations 2 and 4), characterized by cloudy water,
high concentration of humic matter in suspension
and very poor aquatic vegetation, hosted a poor
fauna and in particular at Station 4 no species
was recovered.
Cluster analysis evidenced a low degree of
similarity among the ponds (Fig. 4). Station 4
showed a lower similarity as a consequence of
the complete absence of gastrotrich species. The
other two main clusters presented a similarity of
6%. Habitats of the first group (Stations 3 and
5) were the most similar for species composition (similarity 48%) although they were the
farthest from each other: that may be related to
the presence of a very similar rooted and floating vegetation. On the other hand the Stations 1
and 2, very close each to the other, showed a low
similarity (similarity 22%) and a poor aquatic
vegetation. That suggests that the distribution of
gastrotrich species is more related to the presence
of vegetation than to the geographic location of
the biotope, according to the observations by
Kisielewski (1990).
The high species number, 13, recorded in the
temporary biotope (Station 3) confirms the ability of freshwater chaetonotidans to endure the
unfavourable season by means of resistant eggs
(Balsamo & Todaro 2002).
91
CONCLUSIONS
A relatively rich and diversified gastrotrich fauna
was found on Seeland. Twenty-five species of
Chaetonotida new for Denmark were reported
during this study, which add to the 17 species
already known: thus the current knowledge of
Chaetonotida from Denmark reports 28 species
for inland waters and 14 for marine waters.
A relation between richness of gastrotrichs
and presence of aquatic vegetation, which favours periphytic and epibenthic species, is confirmed. The high number of species observed
even in the temporary biotope may be related not
only to the abundance of vegetation but also to
the ability of freshwater gastrotrichs to survive
to unfavourable ecological conditions by producing resistant eggs, an ability shared by few other
freshwater taxa.
The results of this first study are promising,
and suggest the opportunity of carrying on the
faunistic research by increasing the number of
sites considered, and by repeating collections
in different seasons. Taking into account the
high number of freshwater biotopes present in
Denmark, further investigations could greatly
improve the knowledge of the Danish gastrotrich
fauna.
ACKNOWLEDGEMENTS
We thank the kind staff of the Zoological Museum, Natural History Museum of Denmark.
This research was supported by a grant to the first
author from the European Commission’s (FP 6)
Integrated Infrastructure Initiative Programme
SYNTHESYS (DK-TAF).
92
p. grilli, r. m. kristensen & m. balsamo
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