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new lucinid bivalves from hydrocarbon seeps of the western atlantic
127
New lucinid bivalves from hydrocarbon seeps of the Western
Atlantic (Mollusca: Bivalvia: Lucinidae)
JOHN D. TAYLOR & EMILY A. GLOVER
Steenstrupia
Taylor, J. D. & E. A. Glover. New lucinid bivalves from hydrocarbon seeps of the Western Atlantic
(Mollusca: Bivalvia: Lucinidae). – Steenstrupia 30 (2): 127–140. Copenhagen, Denmark. April 2009.
ISSN 0375-2909.
Four new species of marine bivalve molluscs from the chemosymbiotic family Lucinidae are described
from deeper water of the Western Atlantic. Graecina colombiensis sp. n. from 366 m off Colombia has
prominent lateral teeth and is similar to the genotype Graecina karinae from a seep off West Africa.
Three other species lack lateral teeth and are placed in a new genus, Jorgenia; the type species, J.
louisiana sp. n., is a relatively large-shelled species inhabiting hydrocarbon seeps at around 550 m off
the southern USA, with Jorgenia gracile sp. n. from 600 m off Colombia and J. luteophila sp.n. from
600–850 m off Louisiana. "Loripes" compressa Dall, 1881 described from 775 m off Cuba may be
a juvenile Jorgenia specimen. From shell characters, a relationship of the new taxa with the 'Myrtea'
group of lucinids is suggested but no anatomical or molecular data is available. Other Lucinidae recorded from hydrocarbon seeps are briefly reviewed.
Keywords: Bivalvia, Lucinidae, Western Atlantic, new species, new genus, chemosymbiosis, cold
seeps
John D. Taylor & Emily A. Glover: Department of Zoology, The Natural History Museum, London
SW7 5BD United Kingdom. E-mail: [email protected]; [email protected]
INTRODUCTION
Amongst those bivalve families possessing sym­
biosis with chemolithotrophic sulphide-oxidi­sing
bacteria (Fisher 1990, Distel 1998), the Luci­nidae
is by far the most diverse and disparate in mor­
phology (Reid & Brand 1986; Taylor & Glover
2000, 2006). Lucinids occur at a wide range of
latitudes (60°N–55°S) and at depths to around
2500 metres but they are most diverse and abundant in tropical, shallow-water habitats (Glo­ver
& Taylor 2007). Although some deeper water
lucinids, particularly species of Lucinoma, have
been known for a long time, new explo­rations
of deep-sea habitats, in particular cold seeps and
oxygen minimum zones, are revealing many new
lucinid species (Okutani & Hashimoto 1997;
Salas & Woodside 2002; Bouchet & Cosel 2004;
Holmes, Oliver & Sellanes 2005; Cosel 2006;
Oliver & Holmes 2006; Cosel & Bouchet 2008).
As yet, only a single lucinid, Bathy­austriella
thionipta, has been recorded from a hydro­thermal
vent (Glover, Taylor & Rowden 2004).
Steenstrupia 30 (2): 127–140.
The lucinid fauna of the Western Atlantic
bordering the USA is relatively well known with
reviews by Britton (1970), Bretsky (1976) and
recently, Mikkelsen & Bieler (2007). The deeper
water fauna (> 200 m) includes several species of
Lucinoma, namely L. filosa (Stimpson, 1851), L.
blakeana (Bush, 1893) and L. atlantis McLean,
1936; as well as several Myrtea-like species of
uncertain generic assignments: Myrtea (Eu­lopia)
sagrinata (Dall, 1886), "Myrtea" pri­stiphora
Dall & Simpson, 1901, "Myrteopsis" lens (Ver­rill
& Smith, 1880 in Verrill 1880) and "Myrte­opsis"
compressa (Dall, 1881).
Investigations of offshore hydrocarbon seeps
off Louisiana in the Gulf of Mexico have re­­corded a number of lucinids, including Lucinoma
atlantis and Lucinoma sp. along with the better
studied Bathymodiolus and Calyptogena species.
These lucinids are sufficiently abundant as shells
to identify a "lucinid biofacies" at several loca­
tions (Callender & Powell 1997, 2000). Addi­
128
j. d. taylor & e. a. glover
tionally, Turner (1985) and Brooks et al. (1987)
refer to another lucinid, Pseudomiltha sp., from
the Louisiana seep sites.
While studying collections of Lucinidae in the
USNM we came across samples of two relatively
large, undescribed species, collected at depths of
366 m and 600 m off Colombia in the southern
Caribbean, that differed from all other described
taxa from the Western Atlantic. One of these
species appeared very similar to the specimen
illustrated by García (2002, fig. 7) collected
from a 555 m hydrocarbon seep off Louisiana
and identified as Lucinoma sp. It is also similar to a specimen figured by Turner (1985, fig.
2E–F) from the Louisiana Slope at 600–700 m
and identified as ?Pseudomiltha. Emilio García
kind­ly loaned us his lucinid material from the
Gulf of Mexico seep sites and we have images
of Turner’s specimen (MCZ), confirming that
the Lucinoma sp. and the Pseudomiltha sp. cited
in various reports are indeed the same animal
and part of the same species group as one of the
Colombian specimens.
In this paper we describe four new species
of Lucinidae from the Gulf of Mexico and the
southern Caribbean. One of the species we clas­
sify in Graecina, a genus recently described from
a cold seep off West Africa (Cosel 2006), while
the other three species are included within a new
genus named for Jørgen Knudsen in re­cognition
of his distinguished contribution to our know­
ledge of deep-sea bivalves.
ABBREVIATIONS
BMNH – The Natural History Museum, London,
UK
EFG – Emilio F. García Collection, Lafayette,
Louisiana, USA
MCZ – Museum of Comparative Zoology, Har­
vard University, Cambridge, Massachusetts,
USA
USNM – United States National Museum of
Natural History, Washington, D.C., USA
H – shell height
L – shell length
LV – left valve
RV – right valve
T – tumidity of single valve
SYSTEMATIC DESCRIPTIONS
Family Lucinidae Fleming, 1828
Graecina Cosel, 2006
Type species: Graecina karinae Cosel, 2006. Eastern Atlantic, northern Angola.
Diagnosis (abridged from Cosel 2006)
Subcircular, slightly longer than high, com­
pressed. Sculpture of thin commarginal lamellae
in umbonal area but rest of valve with low growth
increments. Anterior dorsal area marked by ra­
dial depressions; posterior dorsal area indistinct.
Lunule long, narrow, slightly asymmetric, sunk­
en. Escutcheon long, narrow with elevated
dorsal edges. Hinge of RV with one (possibly
two) cardinal tooth and anterior and posterior
lateral teeth. LV with two cardinal teeth and
well-developed anterior and posterior laterals.
An­terior adductor scar elongate, detached from
pallial line for ½ to 2/3 of length. Shell margin
smooth.
Remarks
The name Graecina was introduced for a single
species, G. karinae, described from a possible
cold seep at a depth of 360 m off northern An­
gola.
Graecina colombiensis sp. n.
Figs 1A–J, 2A
Material examined:
Type material. – Holotype: complete shell (USNM 765263),
L 51.6 mm, H 44.6 mm, T 10.1 mm. ca 30 miles NE of Barranquilla, Colombia, 11°29' N, 74°28' W, 200 fathoms (366
m), R. V. Oregon st. 4840, 16 May 1964. Paratype: complete
shell (USNM 1116113), L 46.5 mm, H 41.2 mm T 8.5 mm,
locality as holotype.
Description
Medium large in size, L to 51.6 mm, H to 44.6
mm, subcircular, slightly longer than high, H/L
Fig. 1. Graecina colombiensis sp. n. – A–G. Holotype
(USNM 765263). A, B. Exterior of right and left valves.
C, D. Interior of right and left valves. E. Dorsal view. F, G.
Detail of hinge teeth. – H–J. Paratype (USNM 1116113). H.
Exterior of left valve. I, J. Interior of right and left valves. –
Scale bars = 10 mm.
new lucinid bivalves from hydrocarbon seeps of the western atlantic
129
130
j. d. taylor & e. a. glover
Fig. 2. Outline drawings of interior of left valves. A. Graecina colombiensis sp. n. B. Jorgenia louisiana sp. n. C. Jorgenia
gracile sp. n. D. Jorgenia luteophila sp. n. – Not to scale.
= 0.86–0.89, thin shelled, compressed, slender
(T/L = 0.18–0.20), anterior and posterior margins
slightly truncate. Posterior dorsal area marked
by low sulcus. Umbones low, located anterior of
mid line. Posterior dorsal margin gently curved,
anterior dorsal margin straight. Periostracum
green­ish-brown, conspicuous. Sculpture of very
low, narrow growth increments. Lunule long,
narrowly lanceolate, impressed, symmetrical
with elevated dorsal edges. Escutcheon long,
narrow, with elevated, narrow dorsal edges.
Ligament long, 36% of shell length, set in deep
groove. Hinge teeth of RV with large, anterior,
lateral tooth extending as a narrow ridge towards
umbones, a single, small, curved cardinal tooth,
Fig. 3. Jorgenia louisiana sp. n. – A– G. Holotype ( USNM
1116114). A. Exterior of right valve. B, C. Interior of right
and left valves. D. Dorsal view. E, F. Detail of hinge of right
and left valves. G. Interior of anterior part of right valve
with anterior adductor muscle scar and finely grooved shell
within pallial line. – H–I. Paratype (USNM 1116115). H.
Exterior of left valve. I, Interior of right valve. J. Paratype
(EFG 24040) exterior of right valve. – Scale bars = 10 mm,
except E, F = 5 mm.
new lucinid bivalves from hydrocarbon seeps of the western atlantic
131
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j. d. taylor & e. a. glover
new lucinid bivalves from hydrocarbon seeps of the western atlantic
and a nar­rowly elongate posterior lateral tooth.
LV with anterior and posterior lateral teeth and a
single, small, curved cardinal. Anterior adductor
muscle scar medium-long, ventrally detached
from pallial line for about 2/3 of length (Fig. 2A).
Anterior pedal retractor scar lies dorsal to and
separated from adductor scar. Posterior adductor
scar small, reniform. Pallial line thin, continuous. Pallial blood vessel impression not visible.
Shell interior dull, with some radial striations.
Shell outside pallial line glossy with low radial
stria­tions. Shell margin smooth. Shell colour
creamy-white.
Etymology
Named for the country of the type locality,
Colombia, South America (adjective).
Remarks
We place G. colombiensis in Graecina because of
the similarity of shell shape, lunule, escutch­eon,
and anterior adductor muscle scar char­acters to
those of the type species, G. karinae. The hinge
teeth are also similar with strong lateral teeth, but
G. colombiensis has only single cardinal teeth in
each valve, compared with two (one vestigial in
RV) in G. karinae.
Jorgenia n. gen.
Type species: Jorgenia louisiana new species.
Description
Medium sized, length to around 60 mm. Shells
longer than high, relatively flat shelled, ventral
margin rounded, anterior and posterior margins
slightly truncate. Sculpture largely of fine growth
lines, with low commarginal lamellae in umbonal
area. Lunule long, narrowly lanceolate, deeply
impressed, asymmetric, with elevated dorsal
edges. Escutcheon long also with elevated dorsal
edges – dentate in juvenile shells. Ligament long,
ca. 40% of shell length. Hinge teeth with one or
two small cardinal tooth in each valve; lateral
teeth absent in adult shells, hint of an anterior
Fig. 4. Jorgenia gracile sp. n. Holotype (USNM 752714). A,
B. Exterior of left and right valves. C, D. Interior of left and
right valves. E. Dorsal view.2 F, G. Detail of hinge areas of left
and right valves. – Scale bars A–E =10 mm; F, G = 5 mm.
133
ridge in juveniles. Anterior adductor muscle scar
short, dorsal part wider than ventral part that is
detached from pallial line for ½ to 1/5 of length.
Inner ventral margin smooth.
Etymology
Named for Jørgen Knudsen in recognition of his
distinguished contribution to the systematics of
deep-water bivalves (neuter).
Remarks
Although externally species of Jorgenia appear
superficially similar to Graecina karinae and
G. colombiensis described above, those species
have prominent anterior and posterior lateral
teeth in both valves, while members of Jorgenia
lack lateral teeth.
One of the species described below (J. louisi­
ana) has previously been placed in Lucinoma
Dall, 1901 or Pseudomiltha Fischer, 1887. Luci­
noma species (type species Lucina filosa Stimp­
son, 1851) usually possess prominent, evenly
spaced, commarginal lamellae, two large cardi­
nal teeth in each valve, usually an anterior lateral
tooth and a long, thin, anterior adductor muscle
scar, ventrally detached from the pallial line for
about ¾ of its length. Pseudomiltha (type species
L. gigantea Deshayes, 1825 from the Eocene of
France) is an extinct genus with species having
relatively smooth shells, an extremely long and
thin anterior adductor muscle scar detached from
the pallial line for 90% of its length and totally
lacking hinge teeth.
Shell characters of the species included in Jor­
genia suggest a relationship with the "Myr­tea"
group of Lucinidae. These characters are most
prominent in juvenile shells, and include spinose
dorsal areas, the relatively short ad­ductor muscle
scars, the very small cardinal teeth and a long,
lanceolate lunule.
Jorgenia louisiana sp. n.
Figs 2B, 3A–J
?Pseudomiltha sp. – Turner 1985: 26, figs 2e–f.
Lucinoma sp. – García 2002: 28, fig. 7.
Material examined:
Type material. – Holotype: complete shell (USNM 1116114,
prev. EFG 24040), L 54.4, H 43.5, T 9.7 mm, "Bush Hill" site,
hydrocarbon seep, Louisiana, USA, 27°46.904' N, 91°30.286'
134
j. d. taylor & e. a. glover
W, 546–555 m. Paratypes: figured paratype (Fig. 3J), one
shell (USNM 1116115), same locality, L 49.2, H 40.7 T 7.0;
unfigured paratypes, two shells (EFG 24040), same locality, L
60.7, H 52.0, T 15.8; L 53.8 H 45.4, T 11.5; figured paratype
(Fig. 3H, I), one shell (USNM 1116116, prev. EFG 28316),
L 49.7 mm, H 41.9 mm, T 10.5 mm, Gulf of Mexico, off
Yucatan, 22°46.25' N, 90°16.52' W, dredge, 350 m, mud, NSF
II.121; unfigured paratypes, two shells (MCZ 360374), off
Louisiana, 27°45' N, 91°14' W, 600–800 m, seep site.
Description
Shells medium-large, L to 61mm, H to 52 mm,
subcircular, slightly longer than high, H/L =
0.83–0.86, compressed, slender (T/L = 0.21–
0.26), anterior and posterior margins slightly
trun­cate. Umbones low, located slightly anterior
of mid-line. Anterior dorsal area marked by low,
irregular crumpled sulci. Posterior dorsal area
marked by low sulcus. Posterior dorsal margin
gently cur­ved, anterior dorsal margin straight. Periostracum conspicuous, reddish-brown. Sculp­
ture of very low, narrow, com­marginal growth
increments. Lunule long, nar­rowly lanceolate,
impressed, with elevated dor­sal edges, covered in
thickened, dark perio­stracum. Escutcheon long,
narrow, with ele­vated, narrow, dorsal edges.
Ligament very long, 42 % of shell length, curved,
slightly protruding above dorsal shell margin.
Hinge of RV with a single, narrow, anterior
cardinal tooth, with to the posterior a triangular
toothless hinge plate (Fig. 3E–F), an anterior
ridge on some shells may represent a vestigial
lateral tooth; LV with a single, very thin cardinal
tooth, lateral teeth absent. Anterior adductor
muscle scar medium-long, broader dorsally,
ven­trally detached from pallial line for about 3/5
of length (Fig. 2B, 3G). Anterior pedal retractor
scar lies dorsal to and separated from adductor
scar. Posterior adductor scar reniform. Pallial line
thin, continuous. Pallial blood vessel im­pression
absent. Shell interior within pallial line dull, with
fine radial striations (Fig. 3G). Shell outside pallial line glossy. Shell margin smooth. Shell colour
creamy-white.
Etymology
Named for the state of Louisiana (noun in ap­
position).
Remarks
This species has been referred to as Pseudo­miltha
sp. or Lucinoma sp. in publications con­cerning
the faunas of Louisiana seeps (Tur­ner 1985;
Brooks et al. 1987; Callender & Powell 1997,
2000; García 2002). See remarks under the generic description above.
Jorgenia louisiana occurs with Lucinoma at­
lantis McLean, 1936 at the type locality (García
2002; confirmed by specimens (EFG 24039)
in García collection) and at other hydrocarbon
seeps on the Louisiana slope (Callender & Po­
well 1997, 2000).
Jorgenia gracile sp. n.
Figs 2C, 4A–G
Material examined:
Type material. – Holotype: complete shell (USNM 752714),
L 43.7 mm, H 35.0 mm, T 7.2 mm, off Santa Marta, Colombia,
11°18' N, 74°44' W, 328 fathoms (600 m), R.V. Oregon II, st.
11248, 9 Nov 1970.
Description
Shell length to 44 mm, H to 35 mm, longer
than high, H/L = 0.8, relatively flat shelled, T/L
= 0.16, ventral margin curved, anterior and pos­
terior margins truncately rounded, dorsal margin
rela­tively straight. Surface sculpture largely
of fine growth increments, but low, thin, com­
marginal lamellae more prominent in dorsal part
of valve. Periostracum prominent, pale greenishbrown. Posterior dorsal area demarcated by a low
sulcus and faint radial lines and by more prominent growth increments. Anterior dorsal area
wide, with 3–4 shallow, narrow sulci, marked by
lines running from anterior margin to umbones.
Lunule lanceolate, narrow, long, slight­ly asymmetrical, larger part in LV, set in groove that
deepens anteriorly. Escutcheon long, narrow,
with sharp dorsal edges.
Ligament very long, 48 % of shell length, narFig. 5. Jorgenia luteophila sp. n. – A–C. Holotype (USNM
1116117). A. Exterior of right valve. B, C. Interior of left and
right valves. Numbers on valves are from original García
collection. – D–G. Paratype (EFG 27398). D. Exterior of left
valve E, F. Interior of right and left valves. G. Detail of F
showing hinge. – H, I. Juvenile shells left side. J–L. Exterior
of LV and interior of both valves. – Scale bars A–F = 10 mm,
H–L = 5 mm.
new lucinid bivalves from hydrocarbon seeps of the western atlantic
135
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j. d. taylor & e. a. glover
Fig. 6. ?Jorgenia compressa Dall, 1881. Syntype (USNM 64268 ). A. Exterior of left valve. B, C. Interior of left and right valves.
D. Detail of right valve. – Scale bars = 5 mm.
row, slightly curved. Hinge plate narrow, straight.
Lateral teeth absent on LV, a single, small,
rounded, cardinal tooth present. Lateral teeth
absent on RV, no cardinal teeth but with indistinct
socket for cardinal of LV. Anterior adductor muscle scar relatively short, ventrally detached from
pallial line for just under half of length (Fig. 2C).
Anterior pedal muscle scar dorsal to and detached
from adductor scar. Posterior adductor scar reniform. Pallial line narrow continuous. Inner shell
surface within pallial line with radial striations,
pallial blood vessel trace absent. Shell outside
pallial line glossy with fine radial grooves. Shell
margin smooth. Shell colour creamy-white.
Etymology
Latin adjective gracile meaning slender, in ref­
erence to the slender shell.
Remarks
Jorgenia gracile differs from J. louisiana in possessing a straight rather than curved pos­terior
hinge line, more prominent anterior and posterior sulci and a shorter, more deeply im­pressed
lu­nule.
new lucinid bivalves from hydrocarbon seeps of the western atlantic
Jorgenia luteophila sp. n.
Figs 2D, 5A–L
Material examined:
Type material. – Holotype: complete shell (USNM 1116117,
prev. EFG 27398), L 27.1 mm, H 22.1 mm, T 4.0 mm, Louisiana, USA, 28°06.52' to 28°07.21' N, 89°36.99' to 89°46.57'
W, 850–610 m, mud, benthic skimmer dredge. Paratype:
complete shell (EFG 27398), same locality, L 22.9 mm, H
18.3 mm, T 3.3 mm (Figs 5D–G).
Other material. – Three shells (EFG 24457), Louisiana, USA,
27°43.4’N, 91°16.74’W, 640–680 m, box corer, 2 July 2003
(Figs 5H–L): L18.7, H 14.6; L 9,5, H 6.9; L 8.4, H 6.3.
Description
Shell L to 27 mm, H to 22.1 mm, longer than
high (H/L = 0.8–0.82), relatively flat shelled (T/L
= 0.14–0.15), ventral margin curved, anterior
and posterior margins truncately rounded, posterior dorsal margin relatively straight, anterior
dorsal margin concave. Umbones small, low.
Perio­stracum prominent, pale greenish buff in
colour. Surface sculpture largely of fine growth
lines with thin commarginal lamellae prominent
in dorsal part of valve (to around 8 mm from
um­bones) and along anterior and posterior
dorsal margins. Posterior dorsal area with more
pro­minent growth increments, demarcated by
a low sulcus. Anterior dorsal area wide with
crumpled appearance, with three to four, shallow,
narrow sulci. Lunule lanceolate, narrow, long,
im­pressed, dorsal edges elevated and dentate.
Es­cutcheon long, narrow, straight, with dentate
dorsal edges.
Ligament long, 41% of shell length, straight,
narrow, deeply inset. Hinge plate narrow. Lateral
teeth absent on LV, two narrow cardinal teeth,
the anterior thinner. RV with low ridge extending from anterior adductor scar to cardinal area
(pos­sibly representing anterior lateral tooth), a
single cardinal tooth, posterior lateral absent.
Pallial line narrow, continuous. Anterior adductor scar medium-long, broader dorsally, ventrally
de­tached from pallial line for just under half of
length. Anterior pedal muscle scar located dorsal
to and detached from adductor scar. Posterior adductor scar reniform. Inner shell surface within
pallial line with radial striations, impression of
pallial blood vessel absent. Shell outside pallial
line glossy with fine radial grooves. Shell margin
smooth. Shell colour creamy-white.
137
Three small individuals of less than 20 mm
shell height from non-type locality (Figs 5H–L),
but which we regard as likely conspecific, pos­
sess prominent, regularly spaced, com­marginal
lamellae and spinose posterior dorsal margins.
Smallest individual (L 8.4 mm) with short an­
terior lateral tooth in RV only.
Etymology
Derived from Latin luteus – mud and Greek
phileo – to love and meaning mud-loving (ad­
jective).
Remarks
We consider that all the shells in Fig. 5 are probably juveniles but represent a distinct spe­cies
from J. gracile and J. louisiana. They differ
from J. louisiana in having two cardinal teeth in
the left valve as opposed to a single tooth and a
long straight escutcheon and ligament as op­posed
to the curved posterior dorsal margin. Jorgenia
luteophila differs from J. gracile in possessing well-defined cardinal teeth in both valves,
a shorter, more deeply impressed lunule and a
shorter detached portion of the anterior adductor
muscle scar.
In addition to the new species described above,
there is a small species of uncertain generic status, described by Dall (1881) from off Cuba and
known only from the syntypes. This resembles
the small juveniles of Jorgenia lu­teophila and we
suspect that it may belong in Jorgenia. However,
a more definitive assess­ment of the status of this
species awaits the recovery of larger samples of
growth stages of J. luteo­phila and other species.
For comparison, we figure and briefly describe
the syntype below.
?Jorgenia compressa (Dall, 1881)
Figs 6A–D
Loripes compressa Dall, 1881: 135.
Myrtaea compressa. – Dall 1901: 804.
Myrtea compressa. – Lamy 1920: 220.
Myrtea (Myrteopsis) compressa. – Britton 1970: 379 (un­
published PhD thesis).
Material examined:
Type material. – Syntype: two valves (USNM 64286), L 10.6
mm, H 8.5 mm, off Cabo San Antonio, Cuba, 424 fathoms
(775 m).
138
j. d. taylor & e. a. glover
Remarks
This species has been variously called Myrtea
compressa (e.g. Dall 1901) or Myrtea (Myr­te­
opsis) compressa (by Britton 1970). It was erro­
neously synonymised with Myrtea (Myr­teopsis)
lens (Verrill & Smith, 1880) by Bretsky (1976)
following Dall’s (1901) suggestion that it was
possibly a variant of the latter. However, the two
species are quite distinct. The genus Myr­teopsis
Sacco, 1901 (type species Myrtea (Myr­teopsis)
taurolaevis Sacco, 1901 nomen nudum ? = M.
magnotaurina Sacco, 1901; latter accepted as
type species, see Bretsky 1976: 298) was de­
scribed from the Late Miocene of Italy. We have
not seen specimens of the type species, but from
Sacco’s figures and description (1901: 96, pl.
21 figs 32–36) and images of the type material
sup­plied by Daniele Ormezzano (Museo Regi­
onale di Scienze Naturali di Torino) it does not
seem very similar in either external shell or hinge
characters to L. compressa or Myrtea lens, the
two species from the West Atlantic often placed
in the genus (Britton 1970, Bretsky 1976, Mik­
kelsen & Bieler 2007).
DISCUSSION
It is surprising that these relatively large bivalves
from a well-documented region of the world have
remained undescribed. Jorgenia louisiana and J.
luteophila from offshore Louisiana are definitely
associated with hydrocarbon seeps. We have no
information on the habitat of the collection sites
for Graecina colombiensis and Jorgenia gracile
dredged off Colombia, but their presence to­
gether with Calyptogena and Vesi­comya species
(Boss 1968) would suggest the existence of seeps
in the area.
It often appears that Lucinidae are more abun­­
dant at fossil than Recent seeps; for example,
Lucinoma species in some Japanese Pliocene
deposits (Majima et al. 2003). However, it is
likely that the burrowing infaunal component of
communities at Recent seeps has been less well
investigated than the epifaunal molluscs such as
Bathymodiolus and vesicomyid clams (Carney
1994, Sibuet & Olu 1998, Cordes et al. 2007).
At the shallower seeps on the Louisiana Slope
lu­cinids, as dead shells, have been re­corded in
sufficient abundance to define a lucinid biofacies
(Callender & Powell 1997, 2000). The latter
authors record Jorgenia louisiana (as Lucinoma
sp.) occurring together with the other chemo­
symbiotic bivalve species Lucinoma at­lantis,
Thy­asira oleophila Clarke, 1989, Vesico­mya
cordata Boss, 1968 and Bathymodiolus sp.
Elsewhere, Lucinoma species have been the
most frequently recorded Lucinidae at cold seeps
(Hashimoto et al. 1995, Salas & Woodside 2002,
Holmes et al. 2005, Cosel 2006, Oliver & Holmes 2006), although the "Lucinoma spec­tabilis"
recorded by Hashimoto et al. (1995) was later
described as Mesolinga soliditesta Okutani &
Hashimoto, 1997. Other seep-associated luci­
nids include Graecina karinae, which occurs
with Lucinoma myriamae Cosel, 2006 at seeps
off West Africa, while Myrtea amorpha (Stu­
rany, 1896) is recorded from mud volcanoes
in the eastern Mediterranean (Olu-LeRoy et al.
2004), and Meganodontia acetabulum Bouchet
& Cosel, 2004 occurs with Lucinoma at a likely
hydrocarbon seep off Taiwan.
Although data are patchy, it seems that sig­
nificant populations of deeper water lucinids
are present only at locations with some organic
en­richment, including sites of accumulation of
sunken vegetation (Indonesia and Philippines:
von Cosel & P. Bouchet 2008), oxygen minimum
zones (Cary et al. 1989, Levin et al. 2000, Oliver
& Holmes 2006), hydro­carbon seeps and mud
volcanoes.
Unfortunately, lack of suitably preserved samples for any of the new species has precluded any
molecular analysis to determine the rela­tionships
of these new taxa with other Lucinidae or even
any anatomical study. Morphological characters
of the shell of Jorgenia (commarginal lamellae, spinose dorsal margins, long sharp-edged
escutcheon and small cardinal teeth) suggest a
relationship with the Myrtea group of genera.
Cosel (2006) had already suggested that Grae­
cina karinae might be related to Myrtea. In the
molecular phylogenies for Lucinidae pub­lished
to date, Myrtea and Notomyrtea species occupy
a near basal position in the trees and are distant
from Lucinoma species which group as a sister
clade to Codakia and Ctena (Williams et al. 2004,
Taylor & Glover 2006, unpublished data).
new lucinid bivalves from hydrocarbon seeps of the western atlantic
ACKNOWLEDGEMENTS
We are extremely grateful to Emilio García for
the loan of important material that formed a sig­
nificant part of this paper. The specimens were
collected from the Gulf of Mexico during work
supported by the National Science Foun­dation
under Grant No. 0315995.
We thank Ellen Strong (USNM) for images
of the type of Loripes compressa, Paul Green-
139
hall (USNM) for loan of specimens and Adam
Bal­dinger (MCZ) for access to collections. Daniele Ormezzano (Museo Regionale di Scienze
Natu­rali di Torino) kindly provided images of
Sacco specimens. We are grateful to Harry Taylor
(NHM, London) for the excellent images and to
the Department of Zoology (NHM) for con­ti­
nuing support and travel funding to participate
in the symposium in honour of Jørgen Knudsen’s
90th birthday, March 2008.
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