A new deep-water species of the genus Epilepton (Bivalvia : Galeommatoidea) from the Atlantic

2007·4.3 MB·English

by  J A Allen

THE VELIGER
TheVeliger49(1):7-14(March 30, 2007) i& CMS, Inc., 2006
A New Deep-Water Species of the Genus Epilepton (Bivalvia:
Galeommatoidea) from the Atlantic
ALLEN
J. A.
University Marine Biological Station, Millport, Isle ofCumbrae, KA28 OEG, Scotland
(e-mail: [email protected])
Abstract. Anew species ofthe genus Epileptonisdescribed from the Atlantic. This is the first species ofthe genus
to be described from abyssal depths. Described species of the genus that occur in the Atlantic are listed, and the
relationship between Epilepton and Neolepton is discussed.
INTRODUCTION Genus Epilepton Dall, 1899
Species of the Galeommatoidea have been described Type species by monotypy: Lepton clarkiae Clark,
mostly from shallow waters (e.g., Dall, 1899; Popham, 1852
1940; Chavan, 1959; Boss, 1965; Ponder, 1971; Morton Shell small (<3 mm total length), fragile, equivalve
8l Scott, 1989; Aartsen, 1996a and b; Salas & Gofas, and somewhat compressed, inequilateral, anteriorly
1998; Giribet & Peiias, 1998). Recent sampHng by extended, ovate or subtrapezoidal, with maximum
American research vessels in the Atlantic has shown length ventral to mid-height giving a somewhat dor-
that they also occur at abyssal depths (Allen, 2000) (see sally angulate appearance. White or pale fawn in
&
Allen Sanders, 1996, for description ofthe extent of colour, with fine irregular commarginal growth lines
these studies). Many ofthe described species are either and, in some species, faint radial lines. Hingeplatewith
commensal or epiparasitic. The species described here elongate anterior and posterior lateral teeth in each
is sub-trapezoidal in shape and resembles Epilepton valve, single slightly oblique cardinal tooth anterior to
subtrigonum (Jeffreys, 1875) from the West European umbo in each valve, the left cardinal usually smaller
Basin, and a Mediterranean species Lepton solidnlum than right. Internal ligament, ventral and posterior to
(Gaglini, 1991). umbo, with a fine, barely visible external hgament
The name Epilepton was introduced by Dall (1899) present in some species. Anterior mantle margin of
withoutexplanation. Epilepton, togetherwithNeolepton pedal aperture with sensory papillae.
Monterosato, 1875, Lutetina Velain, 1876, and Plani- The following Atlantic species are recognized:-
kellia Cossmann, 1887, were listed by Dall (1899) as
Epilepton clarkiae (Clark, 1852)
subgenera of Lepton in the family Leptonidae. Again,
no reason was given for this. Later, Epilepton and Figs, lb & 5c
NeoleptonwereincludedinthefamilyNeoleptonidaeby
Theile (1935) and which he included within the Type locality: Coralline zone off mid-south coast
UK
Cyamacea. Thereafter, this arrangement was followed Devon,
by most authorities (Bowden & Heppell, 1968) until Typematerial: Syntypes, U.S.National Museum 199440
recently, Epilepton clarkiae (Clark, 1852) and a new
species ofEpilepton (E. parrussetensis Giribet & Peiias, Lepton clarkiae Clark, 1852: 191
1998) were included in the Montacutidae (Salas & Epilepton clarkiae, Dall, 1899: 876
Gofas, 1998). In transferring Epilepton to the Mon- Epilepton clcvkiae, Tebble, 1966: 87, figures 41a-c
tacutidaeSalas&Gofas(1998)followed Deroux(1961). Epilepton clarkiae, Bowden & Heppell, 1968, 248, 266
Heppel (1964) and Bowden & Heppell (1968) had Epilepton clarkiae, Nordsieck, 1969, 89, plate XIV,
dismissed Deroux's opinion as fallaceous. Nevertheless, figure 50.70
dtihfefehrifngreomantdhosmeanotilNeeoolfedpetsocnri(bseeedSsapleacsie&s oGfofEapsi,le1p9t9o8n Lepatnodn2clarkiae, Waren, 1983: 163, plate 8, figures 1
and Allen, 2000) and are similar in most respects to Epilepton clarkiae, Aartsen, Menkhorst & Gittenber-
montacutid species described by Popham (1940) and ger, 1984: 65, figure 330
Morton & Scott (1989). Epilepton clarkiae, Aartsen, 1996: 32, 36, figure G
Page 8 The Veliger, Vol. 49, No. 1
Figure 1. Species ofEpilepton. Lateral views ofthe left valves ofa, E. parrussetensis; b. E. clarkicw, c, ^'Potidoma.subtrigouiini
d, E. solidiihan; e, E. elpis; f, E. siibtrigoiniiii. Scale bars = 1 mm.
MNHN
Epilepton claikiae, Salas, 1996, 62 Type material: Holotype, 15.07/4644. Para-
Lepton clarkiae, Salas & Gofas, 1998: 69 types, MNHN and BMNH
Epilepton c/arkiae, Delongueville & Scaillet, 1999: 29 &
Epilepton parrussetensis Giribet Penas, 1998: 118,
1^
figures
Distribution: Southwest European Basin and Mediter-
ranean, upper shelf. Distribution: Northwest Mediterranean, from shelf to
Epilepton parrussetensis Giribet & Peiias, 1998 upper slope depths.
Epilepton solidulwn (Gaglini, 1991)
Fig. la
Type locality: off Vallcarca (Sitges, Barcelona, Fig. Id
41 06'59"N I' 54'23"E), 250-350 m Type locality: offCape Palermo, 90 m
J. A. Allen, 2006 Page 9
Type material: Holotype, Museo Civico di Zoologia di oblique and shailowly curved, postero-dorsal margin
Roma more convex, both anterior and posterior shell limits
ventral to mid-horizontal axis, mid-ventral margin
Lepton soUdnhmu Monterosato, 1875: 12 almost straight or very slightly convex; umbos small,
Lepton solidit/uin, Monterosato, 1878: 68 inwardly turned; hinge- plate broad, each valve with
Lepton solidiiliim Gaglini, 1991: 176, figures 189 and elongate posterior and anterior lateral teeth, small
190
cardinal tooth in each valve; triangular internal
Lepton soliduluni, Aartsen, 1996a: 34, figure F (left ligament posterior to cardinal tooth, elongate opistho-
photograph)
detic submarginal external ligament hardly visible
externally.
Distribution: West European Basin and Mediterranean,
Remarks: As there is only one specimen in the present
from shelfto upper slope depths.
collection (Figure If) theanatomyisnot described. The
Remarks: Monterosato (1875, 1878) hsted a consider- hinge featui^es (Figure 5a) conform to those figured by
able number of bivalve species, some of which he Cerulli-IreUi (1908), as do the other shell features. The
recorded as nov.sp., but without description. Recently, hinge is very similar to that of E. clarkiae Clark
a number of his noinina nuda have been briefly (Waren, 1983) (Figure 5c).
described and figured by Gaglini (1991), thus making Deroux (1961) gave an extensive and comparative
them available for the first time. Included is Lepton description ofa shallow-water species commensal with
soliduluni regarded by Gaglini (1991) as a valid species. the polychaete Polydontes niaxillosus Ranzani, 1817,
This species was also doubtfully recorded by Aarstsen that he identified as "Lepton subtrigonum Jeffreys,
(1996b) and photographed but wrongly identified by 1873," and placed in a new genus Potidoma. He
him as Hemilepton nitidum (Turton, 1822) (Aartsen, thought Potidoma was congeneric with Epilepton
1996a fig. F, left hand photograph). Although the shell clarkiae, not noticing that his new genus would be
is trapezoidal as compared the more ovate shape ofE. a synonym ofEpilepton.
clarkiae and E. parrussetensis (figure 1) the basic The shell that Deroux (1961) describes has a heavy
structure ofthe hinge is the same. blackordarkbrowncoatingalthoughtheshell belowis
white and transluscent. However, the mid-ventral
Epilepton subtrigoniim (Fischer, 1873) margin of the shell Deroux described is not convex
& but concave and the position ofthe umbo and antero-
Figs If 5a
dorsal shell margin differs considerably from the true
Type locality: Fosse de Cape Breton, Biscay E. subtrigonum and to previous accounts about it
(Jeffreys, 1875; Cerulli-IreUi, 1908) (Figure If). The
Type material: Syntypes labelled Lepton n.sp.B of hinge also differs in its structure (Figure 5b) and,
Biscay, Folin, U.S.Nafional Museum 199475 perhaps ofless importance, is the much smaller size of
Cited specimen: deposited in the Museum d'Histoire the original and present specimens of£. subtrigonum as
Naturelle, Paris compared with those described by Deroux (1961). It
should also be pointed out that there is a very great
Lepton subtrigonwn Fischer, 1873, ex Jeffreys ms: 82, difference in their depths of occurrence. The species
plate 2, figure 10 described by Deroux may well be an Epilepton, it is
Lepton subtrigoniim, Cerulli-lrelli, 1908: 2, plate 1, doubtful whether it is identical to the E. subtrigonwn
figures 5a and b that Fischer (1873) described.
Lepton subtrigonum, Waren, 1980: 47
Epilepton elpis n.sp.
&
Material: Thalassa, station z425, 48°27.9'N 09"44.0'W, Figs le, 2, 3, 4 6
700 m., 1 spec. Type locality: North America Basin, 35°50.0'N
m
Distribution: Mid-slope depths in West European 64'57.5'W, 4833
Basin.
Type specimen: Holotype and paratype, Natural
Shell description: Very small <3 mm total length, History Museum, London
subtrapezoidal (length/height ratio: 1/0.72), slender
Material: Atlantis II 24, stafion 121, 35"50.0'N
(length/width ratio: 1/0.41), equivalve, slightly inequi- 65"11.0'W,4800 m., l;stafion 122,35"50.0'N64'57.5'W,
lateral, umbo anterior to midline, white, translucent,
4833 m., 5 spec.
almost invisible very fine, closely packed concentric
striae, dorsal margin close to umbo almost straight and Distribution: Abyssal depths in the North America
parallel to mid-ventral margin, antero-dorsal margin Basin.
Page 10 The Veliger, Vol. 49, No. 1
ant.
Ll CT
Figure3. Epiletonelpisa, internalviewofaleftvalve(station
121) to showdetail ofhinge; dorsal viewofshell (station 121).
Scalebars 1 mm.ALanteriorlateraltooth,CTcardinaltooth,
LI ligament, PL posterior lateral tooth.
vertical line; hinge-plate elongate, posteriorly broad,
less so anteriorly, anterior and posterior lateral teeth at
ventral margin of the hinge-plate slender, single
posteriorly oblique cardinal tooth in each valve, meets
Figure 2. Epileptun clpis a) lateral view ofshell (Station 122) shell margin immediately posterior to beak; internal
fromleft side showingprotrudingfoot and sensory papillaeof ligament short and opisthodetic, lies close to margin of
anterior pedal margin; b) lateral view of shell (Station 121) hinge-plate posterior to cardinal tooth, internal and
from right side. Scale bars = 1 mm. external layers clearly marked, posterior external
ligament of fused periostracum short, very small
mm anterior external ligament present; prodissoconch
Shell description: Small (<6.5 in length), somewhat mm
triangular(sub-trapezoidal) withmaximum shell length extremely large, 1.04 total length.
markedly ventral to mid-horizontal line, elongate Internal morphology: Anterior sensory fold of mantle
(length/height ratio: 1/0.75), slender(length/width ratio: margin ofpedalaperture finely papillate(28 papillae on
1/0.29), extremely fragile, white, in some specimens each mantle edge in a specimen 4 mm. total length),
faint anterior marginal radial ridges correspond to a moderately broad band of mantle glands lie
region of sensory mantle tentacles, few faint growth immediately internal to inner muscular fold of pedal
lines present; umbo moderately prominent, slightly aperture and dorsally delineated by an irregular
anterior to the mid-vertical line; shell margin highly epithelial ridge, sensory folds posterior to the pedal
characteristic, postero-dorsal margin relatively straight gape with eight papillae, simple posterior exhalant and
for short distance before broadly curving to the 'inhalant' apertures the former formed by mantle
posterior limit of shell, antero-dorsal margin slopes fusion the latter by adhesion of the opposing inner
steeply and relatively straight to approximately the mantle folds; anterior and posterior adductor muscles
mid-horizontal line before curving to anterior limit of circular in cross section, posterior adductor slightly
shell and continuing to ventral margin; ventral margin larger than anterior; foot relatively large and broad;
in most specimens shallowly curved, in others almost posterior and anterior retractor muscles well-devel-
straight or even slightly concave posterior to mid- oped; pedal glands present with 5-6 byssal threads; gills
J. A. Allen, 2006 Page 11
Figure4. Epilepton elpisa and b) Internal views ofthe hinge ofthe right and left valves (station 122) to show detail ofthe hinge.
Scale bars = 0.1 mm.
homorhabdic, not plicate, outer demibranch absent, posterior to foot; palps small with approximately 8
inner demibranch with ascending and descending internal ridges; mouth opens to relatively elongate
lamellae composed of approximately 35 filaments, oesophagus, stomach elongate with midgut and style
ventral groove of demibranch not marked, axes of sac combined, hindgut extends anteriorly for a short
ascendinglamellaefusedtobodywall and toeach other distance before turning posteriorly along the dorsal
Pase 12 The Veliger, Vol. 49, No. 1
Figure 6. Epilepton elpis Semidiagrammatic view of the
internal anatomyofa specimen from Station 122 asseen from
AA AR
the right side. anterior adductoi", anterior pedal
retractor, DG digestive gland, FT foot, GE glandular
epithelium, HG hindgut, ID inner demibranch, LI ligament,
PA posterioradductor, PPpalp, PR posteriorpedal retractor,
PS pseudofaeces, SP sensory mantle papillae, ST stomach.
Scale bar = 1 mm.
the genus Erycina but may, on further examination,
Figure 5. Species of Epilepton. Semidiagrammatic illustra- prove to be an Epilepton.
tions of the left hinges of a, E. subtrigomiiu; b, "Potidonia Bivalves of the order Galeommatoidea are notori-
s1u96b6t)r.igoAnLum"an(taefrteirorDelraotuerxa,l19t6o1o)t;h,c,CE.Tclacrakridaiena(laftteoroTtehb,blLeI, ously difficult to identify and there has been consider-
ligament, PL posterior lateral tooth. able debate as to their relationships with other orders.
Salas& Gofas (1998), in particular, have suggested that
margin to pass over posterior adductor to anus; Neolepton is a paedomorphic veneroidean. Certainly
visceral, cerebral and pedal ganglia small, with very the hinge characters ofNeolepton suggest this could be
fine connectives: gonad immature in stained specimen. so (Allen, 2000). In contrast, the hinge of Epilepton
differs considerably from that of Neolepton and the
Remarks: This species is named after Elpis (Hope) the veneroideans. Although, like Neolepton. Epilepton has
only item left in Pandora's box after she had opened it. elongate posterior and anterior lateral hinge teeth
It is a truly abyssal species. It differs from E. clarkiae, instead ofa complex series ofcardinal teeth, Epilepton
E. Parrussetensis, E. solidulum and E. subtrigonum, in has a single cardinal that may or may not be
shell proportions (Figure 1), in differences in the particularly strong. There is a strong case for removing
position of the umbo in relation to the length of the Epilepton from the Neoleptonidae. A transfer to the
shell, the less curved ventralmargin, the less prominent Montacutidae was suggested by Deroux (1961), de-
lateral teeth and the more oblique ligament and bated by Bowden & Heppell (1968), and concurred by
relatively weak cardinal tooth. Salas & Gofas (1998). UnHke Neolepton, Epilepton has
no exhalent siphon. Futhermore, Epilepton has sensory
DISCUSSION
papillae at the mantle edge of the pedal aperture
In addition to the five species listed above, a further (Figure 7), a feature not present in Neolepton.
three Atlantic species may belong to the genus. One, The new species described here differs in one respect
described underthe name Mancikellia divae by Aartsen from described species ofthe family Montacutidae. In
and Carrozza (1997), is considered to be a species of the two specimens in which the soft parts were
Epilepton by Giribet & Peiias (1998). A second, already examined an 'inhalent" aperture was defined by a short
discussed (p. 2), is that described by Deroux (1961) as adhesion of the opposite inner muscular folds of the
"Potidoma subtrigonum." A possible third discovered mantle. Apart from this the mantle margin is similarto
when searching relevant literature was described and other species ofthe family Montacutidae, i.e., a papil-
named by Dall (1899) as Erycina? fernandina. As late sensory fold with the papillae particularly numer-
recognised by Abbott (1974), this does not belong to ous anteriorly, and an exhalent aperture that is not
J. A. Allen, 2006 Page 13
siphonate. It is likely that in E. elpiswater flow into the Boss, K.J. 1965. Symbioticerycinacean bivalves. Malacologia
mmaannttlleegcaapvietyanids tvhiaattthhee panotsetreiroirorpianphialllaetnet'aarpeeartoufrethies BOWD3M:Eo1lN8l,3u-s1Jc9.a5.&2. UDn.ioHneapcpeeal-lC.ard1i9a6c8e.a.ReJvoiusrendalliosft CoofncBhroitlios-h
the point at which the pseudofaeces are voided.
gy 26:237-272.
Epilepton clarkiae and E. parrussetensis are more Cerulli-Irelll S. 1908. Fauna malacologica mariana. Parte
ovate and anteriorly extended than the other species seconda. Leptonidae, Galeommidae, Cardiidae, Chami-
listed here. Nevertheless, the hinge structure is similar dae, Cyprinidae. Veneridae. Palaeontographia italica 14:
(Figure 5), and where described, so too is the internal 1-63 [77-139].
anatomy. At present, there is no reason for them to be Chavan, a. 1959. Remarques surlacharnieredes Erycinacea
separate genera. The sub-trapezoidal shape and the et des Cyamiacea. Bulletin de la Societe geologique de
France 7:712-718.
shallowly curved ventral shell margin, which in thecase Clark, W. 1852. On a new species of Lepton. Annals and
of E. elpis maybe slightly concave mid-ventrally, is Magazine ofNatural History 2nd ser., IX:191-192.
reminiscent of the genus Pseiidopythina and may Dale, W. H. 1899. Synopsis of the Recent and Tertiary
indicate similarity in habit. Species of Pseudopythina Leptonacea of North America and the West Indies.
are commensals that are typically byssally attached to Proceedings of the United States Natural History
other species [e.g., P rugifera (Carpenter, 1864) DeloMnugsueevuimll21e:,873C-.897&. R. Scaillet. 1999. Releve de
attached to Upogebiapugettensis (Dana, 1852), Narchi Fassociation de Epilepton clarkiae (W. Clark, 1852) et
(1963)]. In fact, Epileptori clarkiae, although not ofthis de Mioerycina coarctata (S.V. Wood, 1851) avec Phasco-
shape, has recently been proved to be commensal with lion strombi (Montagu, 1804) en Mediterranee. Apex 14:
Phascolion stromi (Delongueville & Scaillet, 1999). 29-32.
However, the hinge of Pseudopythina is without DErOUX, G. 1961. Rapports taxonomiques d'un Leptonace
aanstseurmioerd athnadt tphoestseirmiiolrainltatyerianlshteaepteh,wiatnhdE.itelmpuisstmabye n1o8n73d)ecCraihtie^r'sLepdteonBisoulhotgriicgoMianriim"neJeIfIf.r9ey9s-1(6n3o.men inidiiiii -
Fischer,P. 1873. In:deFolin, L. (ed.).Explorationdelafosse
be related to the epibyssate habit ofthe two genera. de Cap-Breton en 1872. Les Fonds de la Mer 2:65-84.
Apart from the reduction of the ctenidia to single Gaglini, a. 1991. Terze spigolature ... Monterosatiane.
inner demibranchs as seen in E. elpis, there is little Argonauta VII(l-6 (37)):125-180.
deviation from the typical eulamellibranch anatomy. Giribet, G. & A. Penas. 1998. A new Epilepton species
Reduction of the ctenidia is almost universal in deep- (Bivalvia, Montacutidae) from the Western Mediterra-
sea bivalves, particularly those ofa small size. Thismay nean. Iberus 16:117-121.
Heppell, D. 1964. Recorder's report: marine Mollusca.
simply be related to small size, although respiratory Journal ofConchology 25:308-313.
demands probably differ at great depths due the effect Monterasato, T. a. 1875. Nuova rivista delle Conchiglie
ofpressure on physiological processes. Mediterranee. Atti della Accademia Scienze. Lettere ed
Arti di Palermo 5:1-50.
Acknowledgments. I would like to thank Lorraine Fraser for Monterasato, T. A. 1878. Enumerazione e sinonimia delle
assistance with the SEM photographs. I would also like to conchiglie mediterranee. Giornale Scienze Natural! ed
thank the unknown reviewers who provided valuable sugges- Economiche, Palermo 13:61-115.
tions as to the improvement ofthe manuscript. Morton, B. & P. H. Scott. 1989. The Hong Kong
Galeommatacea (Mollusca: Bivalvia) and their hosts,
LITERATURE CITED with descriptions ofnew species. Asian Marine Biology 6:
129-160.
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Conchilega 28(279):31-36 and 61. 1864) (Bivalvia). Veliger 12:43-52.
Aartsen, J. J. van. & F. Carrozza. 1997. On ""Lasaea^ NORDSIECK, F. 1969. Die europaischen Meeresmuscheln
phimila (S.V. Wood, 1851) and two new bivalves from (Bivalvia). Gustav Fischer: Stuttgart, i-xiii, 256.
European waters: Mancikellia divae n.sp and Kelliopsis Ponder, W. F. 1971. Some New Zealand and subantarctic
jozinae n.sp (Bivalvia: Condylocardiidae and Montacuti- bivalves ofthe Cyamiacia and Leptonacea with descrip-
dae). La Conchiglia 29:28-34. tions ofnew taxa. Records ofthe Dominion Museum 7:
Aartsen, J. J. van., H. P. M. G. Menkhorst & E. 119-141.
Gittenberger. 1984. The marine Mollusca of the Bay POPHAM, M. L. 1940. The mantle cavity of some of the
of Algeciras, Spain, with general note on Mitrlla, Erycinidae. Montacutidae and Galeommatidae with
Marginellidae and Turridae. Bassteria suppl.2:l-135. special reference to the ciliary mechanisms. Journal of
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Neolepton (Bivalvia; Cyamioida; Neoleptonidae) fromthe collected by the Balgim and Fauna I expeditions. Haliotis
Argentine Basin. Malacologia 42:123-129. 25:33-100.
Allen, J. A. & H. L. Sanders. 1996. The zoogeography, Salas, C. & S. Gofas. 1998. Description offour new species
diversity and origin ofthe deep-sea protobranch bivalves of Neolepton Monterosato, 1875 (Mollusca: Bivalvia:
ofthe Atlantic: The epilogue. Progress in Oceanography Neoleptonidae), with comments on the genus and on its
38:95-153. affinity with the Veneracea. Ophelia 48:35-70.
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Majesty's Stationary Office: Edinburgh. 212 pp. chological Society of Great Britain and Ireland, Special
Theile, J. 1935. Handbuch der Systematischen Weichtier- Publication No. 1:60 pp.
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