Mollusca Bivalvia : Archibenthal Nuculidae off New Caledonia

12 Pages·1991·1.5 MB·

by  Wim Bergmans

ILTATS DES CAMPAGNES MUSORSTOM. VOLUME 7 RÉSULTATS DES CAMPAGNES MUSORSTOM. VOLUME 7 RÉSULT
2
Mollusca Bivalvia : Archibenthal
Nuculidae off New Caledonia
Wim BERGMANS
Universiteit van Amsterdam
Instituut voor Taxonomischc Zoologie (Zoôlogisch Muséum)
Postbus 4766, 1009 AT Amsterdam
The Nethcrlands
ABSTRACT
Six spccics of Nuculidae hâve been identified from dredgings strungei (A. Adams, 1856). Ennucula Ircdalc, 1931, is consi¬
between 250 and 430 m off western New Caledonia : Nucula dérai a synonym of Leionucula Quenstedt. 1930. This
nitidulaformis Powell, 1971 : N. kanaka. N. oppressa, and nuculid fauna shows rather strong similaritics to that of New
N. libéra, spp. nov. ; Nucula sp. indet. ; and leionucula Zealand.
RÉSUMÉ
Mollusca Bivalvia : Nuculidae bathyales de Nouvcllc-Calé- Zélande et des îles Chatham. Seule N. libéra ne se rapproche
pas d'une espèce de la Nouvelle-Zélande et. d'une manière
générale, l'ensemble étudié a des rapports morphologiques
Six espèces de Nuculidae ont été identifiées dans des assez étroits avec la faune de Nuculidae de la Nouvelle-
récoltes faites entre 250 et 430 m de profondeur à l'ouest de Zélande. Nucula strungei a été classée dans le genre Leionu¬
la Nouvelle-Calédonie : Nucula nitidulaformis Powell, 1971 ; cula Quenstedt. 1930, qui est caractérisé par l'absence d'une
N. kanaka. N. oppressa et N. libéra, spp. nov. ; Nucula sp. structure radiale intérieure des valves, qui par suite ont des
indet. ; et Leionucula strungei (A. Adams, 1856). N. nitidula¬ bords lisses. Ennucula Iredale, 1931. est considérée comme
formis et L. strungei ont été décrites de la Nouvelle-Zélande. un synonyme de Leionucula. Toutes les autres espèces
N. kanaka montre des similitudes avecN. nitidula A. Adams, rapportées possèdent cette structure et le bord ventral crénelé
1856. de la Nouvelle-Zélande et des îles Chatham, et avec correspondant, et sont classées dans Nucula Lamarck. 1799.
N. beachporlensis Vcrco, 1907, de l'Australie. N. oppressa Dans N. libéra, le bord ventral n’est crénelé qu'à partir d'une
ressemble à Linucula recens Dell, 1956, de la Nouvelle- certaine taille.
Bkrgmans, W„ 1991. Mollusca Bivalvia : Archibenthal Nuculidae off New Caledonia. In : A, Crosnihr & P. Bouchet (eds). Résultats
des Campagnes Musorstom. Volume 7. Mèm. Mus. nain. Hist. nul.. (A). 150 : 29-40. Paris ISBN : 2-85653-180-6.
Publié le 20 mars 1991.
Source : MNHN, Paris
30 WIM BERGMANS
INTRODUCTION
On account of my earlier work on a number of ofiered an obvious opportunity to improve our
Australian Nuculidae (Bergmans, 1978) Dr Phi¬ knowledge and furlher shape ideas on the distri¬
lippe Bouchet of the Muséum national d’His- bution patterns of archibenthal species or species
toire naturelle in Paris invited me to study a aggregates in the Australian-Pacific région, and
collection of Nuculidae from dredgings from ofT related taxonomie concepts, I accepted the offer
the west coast of New Caledonia by the vessel with gratitude. This paper présents the results of
“ Vauban " in 1978 and 1979. As this material this study.
MATERIAL AND METHODS
The material on which this report is based is national d’Histoire naturelle in Paris (mnhn) ;
listed under the species in the taxonomie section. small samples hâve been deposited in the Zoôlo-
Descriptions are in accordance with the termino- gisch Muséum of the University of Amsterdam
logy adopted in Bergmans, 1978, and are ex- (zma). The photographs in this paper hâve been
plained in the Method paragraph of that paper. made with a scanning électron microscope.
The présent collection is housed in the Muséum
SYSTEMATIC ACCOUNT
Nucula nitidulaformis Powell, 1971 Remaining valve part with some pronounced
Figs 1-2 growth Unes and on the médian part more or less
aflected by line inner radial structure, which
Material oxamined. — 1 complété shell. 4 odd corresponds with crenulation of ventral margin.
valves, collected by Ph. Bouchet, 23 May 1978, at Hinge moderately strong, with up to 8 anterior
" Vauban " Stn 2, 22'17' S, 167°14' E. New C aledonia, and 5 posterior V-shaped secondary teeth (in the
dzmepat)h. 425-430 m (1 shell, 3 valves : mnhn ; 1 valve : larges! specimens of this sample). Tooth rows
separated by a small chondrophore with a
Description. Valves small, relatively solid, rounded or slightly angular ventral margin, only
moderately convex, trapezoid ovate in outline. slightly projecling beyond hinge line, directed
Lunule only slightly depressed. Dorsal margin downward and very weakly forward. Dorsal
weakly curved, without médian angulation. Pos- margin somewhat thickened and flattened at
terior margin truncated, straight ; posterodorsal both sides above chondrophore. No discernable
angle not very distinct, posteroventral angle trace of primary teeth. Adductor muscle scars
rather distinct. Anterior margin somewhat trun¬ distinct. Mantle line with shallow incurvation
cated, slightly curved ; dorsal margin gradually just anterior of the middle.
passing into anterior margin, anteroventral an¬ Shells white or tinged with pale brown. Traces
gulation broadly rounded but quite distinct. of transparent light brown periostracum preser-
Ventral margin rounded anteriorly and slightly ved in two specimens.
less so posteriorly. Exterior of embryonic shell Measurements : Table I.
with probably bifid umbo (shells too worn to be
conclusive) and microscopically pitted surface. Discussion. Nucula nitidulaformis was de-
Interdissonconch smooth except growth Unes. scribed from specimens dredged at 366-475 m,
Source : MNHN, Paris
MOLLUSCA BIVALV1A : ARCHIBENTHAL NUCULIDAE 31
Table 1. Measuremcnls in mm and number of sccondary teeth in Nucula niüdulaformis Powell, 1971 from “ Vauban "
Station 2, New Caledonia.
Specimen Length Height (onSee cvtiaolnv e) embshryelol nic Naunmtebreiro ro f secondpaorsyt erteioerth
mnhn (right) 1.84 (1.64) ' 0.60 8 4
7.MA (left) 1.84 1.60 0.56 8 5
MNHN (right)' 1.76 1.48 7 3
mnhn (doublet) 1.56 1.28 0.44 c. 0.34
MNHN (right) (1.48)" 1.28 0.44 0.28 6 4
* Ventral margin incomplète ; ' figured spccimen ; " posterior margin damaged.
east of Aldermen Islands, Bay of Plenty, New Paratypes : 2 left valves, data as for holotype
Zealand. The smallest specimen in the original specimen (mnhn ; zma 3.88.001) ; 1 left valve, collected
lot, the holotype, measures 4.4 mm in length, the b22y° 1P7h'.S B, o1u6c7h°e1t2, 'E2,3 MNeawy 1C9a7l8e,d aotn i“a . Vdaeupbtahn " 3S90tn m3,
largest 7.8 mm. Larger specimens appear to be (MNHN).
relatively high. Possible différences between New
Zealand specimens and New Caledonian ones
are the relatively low number of posterior secon- Diagnosis. Shell small, triangular. relati¬
dary teeth in the latter and the rather perpendi- vely high, smooth except irregular growth lines.
cular orientation of its chondrophore. Powell Chondrophore small but essentially oblique.
(1971) counted 10 anterior and 8 posterior teeth Anterior tooth row continuing above chondro¬
(called posterior and anterior by him, respecti- phore. Ventral margin crenulated.
vely) in one of the Aldermen Islands specimens
without indicating valve length. He described Description. — Valves rather small, modera-
the chondrophore as narrow, spoon-shaped, and tely solid, thickened in the médian area, not
anteriorly oblique. His photographs of the holo¬ much inflated, rounded triangular in outline.
type specimen suggest that its chondrophore Lunule not depressed. Dorsal margin weakly
resembles that of the specimens from New curved, short, gradually passing into long and
Caledonia but unfortunately they are not distinct nearly straight anterior margin and strongly
enough to be conclusive. In this connexion it descending straight posterior margin. Ventral
may be of importance that Powell did not margin evenly rounded. Anteroventral angula¬
assign Nucula niüdulaformis to the genus Pronu- tion rounded, posteroventral angulation rather
cula Hedley, 1902 (considered a synonym of distinct. Umbo pointed. Délimitations of em-
Nucula Lamarck, 1799, by the présent author ; bryonic shell and interdissoconch not discernable
see Bkrgmans, 1978). Although there is a definite in the présent material. Sculpture consisting of
anteriorly directed vector in its orientation, the growth lines and, on the médian area, occasional
chondrophore in the New Caledonian specimens radial lines corresponding with a radial inner
possesses the configuration thought to warrant structure. Ventral margin crenulated by this
récognition of Pronucula by Powell. The pré¬ structure. Hinge without a trace of primary teeth
sent sample appears to be the first to be reported and with rather narrow, V-shaped secondary
after the description of the species. teeth. Nine anterior and five posterior teeth in
largest specimen. Anterior tooth row narrowing
Nucula kanaka sp. nov. otonwe aordr st wchoo nvedrryo pshmoarlel, taenedth c oabnotivneu iint.g Cwhiothn dornol¬y
Figs 3-4 phore small, oriented forwards, parallelling an¬
Material examined. — Holotype : 1 complété shell, terior tooth row ; its ventral margin slightly
collectcd by Ph. Bouchet, 23 May 1978, at "Vau¬ inflated posteriorly and making a rounded angle
ban" Stn 2. 22°17'S, 167°14'E, New Caledonia. with its anterior margin. Adductor muscle scars
depth 425-430 m (mnhn). shallow but distinct. Mantle line simple. One
Source : MNHN, Paris
Fies 1-8. 1-2 : Nucula nitidulaformis Powcll, length 1.76 mm. from 425-430 m al “ Vauban ” Sln 2 (22"17' S. I67”I4' E),
New Caledonia (mnhn). - .3-4 : Nucula kanaka, sp. nov.. righl valve of hololype specimen, length 2.84 mm. from 425-
430 m at “ Vauban " Stn 2 (22°17'S, 167°I4' E), New Caledonia (mnhn). 5-6 : Nucula oppressa, sp. nov.. lefl valve,
holotype specimen, lcnglh 2.84 mm. from 250-350 m at " Vauban" Sln 40 (22"30‘S. I66"24'E). New Caledonia
(mnhn). — 7-8 : Nucula oppressa, sp. nov.. right valve, paralype specimen, length 2.06 mm. data as for holotype
specimen (mnhn).
Source : MNHN, Paris
MOLLUSCA B1VALVIA : ARCHIBENTHAL NUCULIDAE 33
Table 2. Measuremcnts in mm and numbcr of sccondary teeth in Nucula kanaka, sp. nov., from " Vauban " Station 2
and 3, New Catedonia.
Specimen Lcngth Height Section Number of sccondary teeth
(one valve) anterior posterior
Hololype (Stn 2) 2.84 2.48 0.68 right 9 4
left 8 5
Paratype (Stn 2) 2.70 2.44 0.80 9 5
Paratype (Stn 2) 2.40 2.16 0.64 9 4
Paratype (Stn 2) 2.04 1.82 0.60 7 3
Paratype (Stn 3) 2.60 2.25 0.72 8 4
valve with a remnant of a dark brown periostra- Diagnosis. A small, ovate shell with a
cum. truncated posterior side ; essentially smooth :
Measuremcnts : Table 2. with visible inner radial structure in the médian
area and finer, more traverse line structure in
Discussion. — Only the holotype has a well anterior and posterior areas ; typically nuculid
preserved hinge. In lhe paratypes it is difficult to teeth ; a short but very oblique chondrophore ;
see if the chondrophore is rounded and directed and ail margins except the médian part of the
downwards or short and pointing forwards, and dorsal margin crenulated by the inner structure.
if the anterior teeth ascend above it. Nucula
kanaka resembles the New Zealand species Nucu¬ Description. Valves rather small. thin to
la nitidula A. Adams, 1856 sensu Powell (1979 : moderately solid, médian area thickened in a
356, Fig. 83-2), but difiers in outline and details number of the specimens — mostly in larger
of the hinge. It is more produced dorsoposte- valves - , moderately inflated, ovate in outline
riorly, its anterior tooth row is proportionally except for almost perpendicular posterior side.
much narrower posteriorly, and its chondro¬ Radial zone corresponding with straight poste¬
phore is much shorter and directed more for¬ rior margin slightly depressed. Larger valves
wards. Nucula beachportensis Verco, 1907 (see relatively higher. Dorsal margin curved. in
Bkrgmans, 1978, Fig. 15-19), from Australian some specimens with a slight angle beneath
waters, seems also morphologically related to the umbo. Anterodorsal angulation poorly de-
N. kanaka. N. kanaka difiers from it in being fined or absent. Posterodorsal angulation round¬
higher and more triangular, with a proportio¬ ed but distinct. Anterior margin weakly curved.
nally longer posterior margin, a smaller angle partly straight in some specimens. Posterior mar¬
between its tooth rows, and a shorter chondro¬ gin short and straight. Anteroventral junclion
phore. weakly marked, rounded, posteroventral junc-
tion more distinct. Umbo pointed. Embryonic
Etymology. The species name kanaka is shell bifid, surface finely pitted. Interdissoconch
derived from “ Kanak ", the original name of the smooth. Embryonic shell and interdissoconch
people of New Caledonia. without visible radial structure. Remaining part
of valve essentially smooth, with fine growth
fines and in some larger valves a few growth
zones near the margin, mutually separaled by
Nucula oppressa sp. nov. grooves. Central part of valve with inner radial
Figs 5-8 structure appearing as fine fines ; anterior and
posterior parts with still finer and widely diver¬
Material examined. Holotype : 1 left valve, gent fine structure. In a number of specimens.
cSotnll e4c0te, d2 2b°3y0 'A S. , W166a“r2é4n' , li7. NJuewne C 1a9le7d9o. naiat . “d eVpatuhb 2a5n0 "- most of which are quite worn, this finer structure
350 m (MNHN). is hardly or not discernable, especially on lhe
Paratypes : 54 valves, data as for holotype specimen posterior part. Ventral margin crenulated by lhe
(44 valves : mnhn ; 10 valves : zma 3.88.002). radial structure of the central part ; anterior and
Source : MNHN, Paris
34 WIM BERGMANS
posterior margins and adjoining parts of dorsal accommodate small shells from the Tertiary of
margin crenulated by the finer, divaricating New Zealand with weak radial sculpture and
structure. This latter crenulation is difficult to finer radiais on anterior and posterior parts.
trace in the majority of the specimens but most Marwick did not describe the hinge, partly
probably distinct in fresh ones. Hinge without a because it had not been preserved well enough in
trace of primary teeth. Dorsal margin slightly his specimens but his descriptions were very
thickened at both sides above chondrophore. short anyway. Dell (1956a) included Nucula
Chondrophore oblique, directed forwards, relati- gallinacea Finlay, 1930, in Linucula, on account
vely short. Up to about 12 anterior and five of a quite different type of aberrant sculpture on
posterior short, triangular, secondary teeth. An¬ its anterior side ; his figures of this species show a
terior tooth row with two or three small teeth hinge typical of Nucula. Dell (1956a) refiected
above chondrophore. Adductor muscle scars and on the différences between that hinge and the
simple mantle line visible in good specimens. hinge of Linucula recens, suggesting that Linu¬
Periostracum not preserved. cula which he had raised to generic rank
Measurements : Table 3. because of the divergent sculpture on its lunule,
its well-defined geographical range, and its long
Discussion. Of the known nuculids, Linu¬ Tertiary history might consist of two groups.
cula recens Dell, 1956, seems to be the morpho- Bkrgmans (1978) described Nucula brongersmai
logically nearest relative of Nucula oppressa. from New South Wales, Victoria and Tasmania
N. oppressa differs in being less équilatéral, in in Australia, which also has a sculpture of radial
having a relatively larger number of anterior fines and diverging fines on anterior and poste¬
teeth (11 in recens specimens up to 4.04 mm in rior parts, but smooth margins, and a round
length ; Dell, 1956a), in the more oblique and chondrophore separating the tooth rows. While
more elongate form of the chondrophore, and in agreeing that forms of aberrant structure and
the form of the teeth near the chondrophore. In sculpture of anterior and posterior valve parts
oppressa, these teeth do not deviate from the are worth considering in efforts to define natural
normal nuculid type. In recens “ the two central groups within the Nuculidae, I do not think that
teeth of each sériés are larger than their fellows Linucula is well defined, or that the species with
and meet dorsally under the beaks to give the such structure and sculpture are necessarily
appearance of a bifid tooth, the two arms of closely related. Further studies of such species
which form the latéral limits of the chondro¬ should attempt to describe, and preferably illus-
phore ” (Dell, 1956a). (It has occurred to me trate, their hinge configurations in detail.
that this configuration can only exist in one valve
of each specimen, but its counterpart has not Etymology. — The spécifie name oppressa,
been described.) Linucula was described as a derived from the Latin opprimere (to oppress, to
subgenus of Nucula by Marwick (1931), to hide) refers to the inner line structures, oppressed
Table 3. Mcasuremcnts in mm and number of secondary teeth in Nucula oppressa, sp. nov., from " Vauban " Station 40.
New Caledonia.
Specimen Length Height (one valve) aNnutemrbioerr 'o 'f secondpaorsyt etreioetrh
Right valve 3.17 2.79 0.92 10 4
Lcft valve ' 2.92 2.68 0.87 11 5
Right valve 2.75 2.38 0.75 10 4
Right valve 2.58 2.12 0.71 8 4
Right valve 1.88 1.58 0.50 6 3
Right valve 1.54 1.34 0.42 5 2
Holotypc specimen (Ail others : paratype specimens).
Innermost anterior teeth often worn away.
Source : MNHN, Paris
MOLLUSCA BIVALVIA . ARCHIBF.NTHAL NUCULIDAE 35
in the sense that they do not affect the outer shell tooth row and in most specimens distinctly
surface (except the margins) and hidden, or concave beneath it ; posteroventral junction dis¬
difficult to discern, in many specimens. tinct. Ventral margin rather broadly rounded,
especially posteriorly. Umbo rather pointed.
Embryonic shell extremely small, squarish ovate,
Nucula libérasp. nov. with microscopically pitted surface. Interdisso-
conch smooth, polished, its margin distinct in
Figs 9-12 part of the specimens. Remaining outer surface
Material examined. Hololype : 1 complété shell. smooth, sometimes, in large specimens, with
collected by A. Warén, 7 June 1979. at “ Vauban " some slightly raised growth zones, especially near
Stn 40. 22°30' S. 166“24' E. New Caledonia. depth 250- ventral margin. Radial structure weakly visible
350P amra t(ympensh n: )1. 3 complété shells and 246 valves, data at a certain angle of light only. Hinge moderately
as for holotype specimen (10 shells and 231 valves : strong, with up to six anterior and five posterior.
mnhn; 3 shells and 15 valves ; zma 3.88.003). moderately long, secondary teeth. Tooth rows
separated by ovate chondrophore.
Diagnosis. — A small, trapezoid ovate shell, Chondrophore wider than high, not much
with a relatively long posterior side, rather many projecting beyond hinge line, with a weakly
posterior teeth, a partly concave posterior mar- rounded ventral edge. Resilifer roundish triangu-
gin, a smooth outer surface, a weak ovate lar. Dorsal margin thickened at both sides above
chondrophore separating the tooth rows, and in chondrophore. in some specimens with traces of
large specimens a crenulated ventral margin. possible vertical striae on these thickened parts.
In large specimens the inner ventral margin is
Description. Valves small, moderately weakly crenulated. Only in very few specimens a
solid to solid, thickened in the central area in a corresponding structure of radial lines is visible
number of larger specimens, only moderately over a short distance near the crenulations.
inflated, trapezoid ovate in outline. Lunule Adductor scars visible. Mantle line with shallow
slightly inflated, demarcated by a radial déprés¬ incurvation. Periostracum thin, transparent, tinged
sion corresponding with a concavity in the yellowish brown.
posterior margin. Escutcheon not defined. Dor¬ Measuremerts : Table 4.
sal margin straight to slightly concave beneath
the umbo and evenly, although not strongly, Remarks. — Il is quite unusual that the
rounded at the sides ; junction with anterior crenulation of the ventral margin in an appa-
margin graduai or with a distinct angulation rently radially structured Nucula shell is présent
just above the anteriormost tooth, junction only in large, probably adult specimens. and it
with posterior margin graduai. Anterior margin is quite confusing when identifying smooth-mar-
weakly rounded, ventrally straight in some speci¬ gined specimens of this species. The variable
mens ; anteroventral angulation rather distinct. outline, from rather squarish when the antero-
Posterior margin more or less convex along the dorsal angle is distinct and the posterior margin
Tabi.f. 4. Measurements in mm and number of secondary teeth in Nucula libéra sp. nov., from " Vauban " Station 40. New
Caledonia.
Specimen Length Height (onSee cvtiaolnv e) emLbsehrnyeglolt hn ic • nterLdiesnsgotcho nch Naunmtebreiro ro f secondpaorsyt erteioerth
Paratype. left valve 1.62 1.42 0.38 0.22 4 3
Paralype, right valve 1.84 1.62 0.54 0.22 0.70 7 4
Holotype, right valve 2.18 1.88 0.60 0.22 6 4
Holotype, left valve 6 5
Paratype, right valve 2.21 1.96 0.64 0.20 0.76 7 4
Source : MNHN, Paris
36 WIM BERGMANS
nearly straight, along the tooth row, to trapezoid dissoconch indistinct in these rather worn speci¬
ovate when that angulation is not well marked mens. Embryonic shell microscopically pitted
and the posterior margin distinctly curved, adds externally. Rest of valve with fine growth lines,
to the identification problem. A further difficulty which in large specimens may become quite
is that fresh specimens are transparent and worn pronounced near the valve margin, where a few
specimens opaque. Moreover, the valves are of growth zones may develop into concentric
rather variable thickness. It may be problema- riblets. No trace of an inner radial structure or a
tical to identify individual specimens, and it is corresponding sculpture.
fortunate that the type sériés is so large. Anterior hinge plate narrowing towards chon-
drophore and continuing above il. Posterior
Etymology. This species is named libéra, hinge plate rather wide, ils inner margin undu-
meaning free or unrestrained, in memory of Dr lated by the teeth. Chondrophore concave, rath¬
Dick Hillenius, zoologist and writer, for whom er long, projecting beyond hinge plate, oriented
freedom of thought and opinion were synony- toward anteroventral junction of valve margin ;
mous with life itself. Dr Hillenius, a colleague in young specimens (Fig. 14) the chondrophore
at the Instituut voor Taxonomische Zoologie of hardly diverges from the anterior tooth row but
the Universiteit van Amsterdam, died unexpec- after this stage its orientation changes and il
tedly on the 4th of May 1987, at the much too becomes divergent. Up to 15 anterior and seven
early âge of 59. posterior secondary teeth, rather fiat and broad,
with weakly V-shaped basal sections. Adductor
muscle scars distinct. Palliai line distinct, with a
Leionucula strangei (A. Adams, 1856) wide curve upward in the middle (Fig. 14). Shells
Figs 13-14 white or tinged with very pale brown, polished
inside. Periostracum not preserved. Inner ventral
margin smooth.
Nucula strangei A. Adams, 1856 : 52. Measurements : Table 5.
Ennucula strangei - Dell, 1956a : 11, pl. 1, fig. I.
Material examined. 31 valves, collected by Discussion. Dell (1956b) figured an adult
A. Warên, 7 June 1979, at “ Vauban " Stn 40, shallow-water specimen from Wellington Har-
22°30'S, 166"24' Ei, New C'aledonia. depth 250-350 ni bour, measuring 12.3 mm in length, and remark-
(b2y6 Ava. lvWes a:r êmnn, h7n ;J u5 nvea lv1e9s7 9: , zaml a)“ ; V1 avuablvaen," coSltlne ct3e3d, ed that deep-water specimens do not attain a
22°33'S, 166"25' H. New Caledonia, depth 290-350 m very large size. The présent specimens are small,
(MNHN). with a number of them about 7 mm in length,
suggesting that this may be the adult size in
Description. New Caledonian valves up to the population concerned. C'ompared to Dell’s
about 7 mm long, generally rather thin but figure, they are more trapezoid in outline, with a
thickened in the area enclosed by adductor somewhat more truncated anterior margin and a
muscle scars and mantle line, moderately in- slightly less produced posterior side, and only in
flated, broadly trapezoid in outline. Lunule and large specimens a chondrophore resembling that
escutcheon slightly depressed, lunule bordered by in Dell's specimen. Of the Australian smooth-
a weak ridge. Older valves relatively more margined Nuculidae, Nucula loringii A. Adams
convex. Dorsal margin evenly curved, junctions & Angas, 1864 seems related. This species was
with anterior and posterior margins graduai. synonymized with Nucula cumingii Hinds, 1843
Anterior margin very slightly convex in small by Hedley (1913), who figured the type speci¬
specimens and straight or with a weak conca- men, but considered different from that species
vity above the junction with the ventral margin by Iredale (1939), who figured a specimen from
in large specimens. Posterior margin slightly Low Isles, Queensland. To judge from those
concave below tooth row. Ventral margin broad¬ illustrations, loringii has a more produced poste¬
ly rounded, posteriorly somewhat flattened, gra- rior side, a larger angle between the tooth rows,
dually passing into anterior margin but with rath¬ much weaker teeth, and a narrower and longer
er distinct posteroventral angle. Umbo rather chondrophore. Nevertheless, type material of
pointed. Margins of embryonic shell and inter- loringii and strangei should be compared to
Source : MNHN, Paris
MOLLUSCA BIVALVIA : ARCHIBENTHAL NUCULIDAE 37
Eigs 9-15. — 9-10 : Nucula libéra, sp. nov.. righl valve of paralype specimen. lcngth 2.13 mm. from 250-350 m at “ Vauban "
Sin 40 (22'‘30' S, 166'‘24' E). New Calcdonia (mnhn). 11-12 : Nucula libéra, sp. nov., left valve of paralype specimen.
length 1.71 mm, data as for valve of figs 9-10. 13-14 : Ijeionucula strangei (A. Adams), left valve, length 3.25 mm.
from 250-350 m at " Vauban" Stn 40 (22°30'S. 166"24' E). New Caledonia (mniin). 15 : Nucula sp. indet.. length
2.06 mm, from 425-430 m at “ Vauban" Stn 2 (22° 17’ S, 167° 14' E). New Caledonia (mnhn).
Source : MNHN, Paris
38 W1M BERGMANS
Table 5. Measurements in mm and numbcr of secondary teeth in Leionucula s t rangei (A. Adams, 1856) Irom " Vauban "
Station 40. New Caledonia,
Spécimen Length Height (onSee cvtiaolnv e) Naunmtebrciro ro f secondpaorsyt erteioerth
Right valve 7.17 5.50 1.83 14 7
Left valve 7.08 5.50 1.83 14 6
Left valve 6.10 4.71 1.25 12 5
Figured left valve 3.25 2.37 0.67 7 3
assess the possible relationship between the two lation distinct. Ventral margin rounded. Sur¬
forms. Unfortunately, Hedley (1913) offered no face of embryonic shell microscopically pitted.
discussion on this point. Outer surface of valve, including interdisso-
conch, smoolh except very fine growth fines.
Hinge rather strong, with seven anterior and
Nucula sp. indet. four (fourth minute) posterior, short, secondary
Fig. 15 teeth. Anterior tooth row distinctly more narrow
towards chondrophore and continuing above it.
Material examined. I right valve, collected by Chondrophore short, not extending far beyond
Ph. Bouchet, 23 May 1978. at “ Vauban " Stn 2, ventral hinge fine, distinctly forward directed,
2(M2N°1H7N'S)., 167Ü14'E. New Caledonia. depth 425-430 m with its anterior margin bordering anterior
tooth row but separated from posterior tooth
Description. Valve small, very inequilate- row by small interspace. Dorsal margin pecu-
ral. relatively solid, moderately convex. rounded liarly thickened along both tooth rows, with
triangular in outline. Médian part of valve indistinct groove over the length of these, as if
thickened. Lunule somewhat depressed, border- to receive two ridges dorsal to the tooth rows in
ed by an indistinct radial ridge. Dorsal margin the left valve. No trace of primary teeth. Adduc-
consisting of an anterior part which is curved at tor muscle scars visible. Mantle fine with shallow
the ends and straight in the middle, and a very incurvation in the middle. Valve white. Traces of
short, rather straight posterior part ; the two a dark brown periostracum.
parts start beneath the umbo at slightly different Measurements Length 2.06, height 1.84,
levels (the posterior part more ventrally), causing section 0.63 mm : length of embryonic shell 0.23
a slight concavity in the dorsal margin. Antero- and of interdissoconch 0.56 mm.
dorsal junction obtuse, posterodorsal junction
more distinct. Anterior margin weakly convex. Remarks. As there is only one valve of this
Anteroventral junction a broad curve. Posterior apparently undescribed species, and its condition
margin weakly convex along tooth row and very is not perfect, I prefer to leave it without spécifie
weakly concave below it. Posteroventral angu¬ name.
Remarks on the généra Leionucula Quenstedt, 1930, and Ennucula
Iredale, 1931
Iredale’s proposai to place smooth-margined Lamarck, 1799, i. e. Nucula nucléus (Linnaeus,
N ucula species in a separate genus, Ennucula 1758), only. His diagnosis was very short : “ a
Iredale, 1931, has been followed by a number of notably oblique chondrophore, above which the
authors for Australian and New Zealand species. teeth become much smaller, and the angle of
In his diagnosis of Ennucula, Iredale (1931) opposition of the two rows of teeth is scarcely
compared it with the type species of Nucula marked ; further, the edge of the European shell
Source : MNHN, Paris