Notes on the identity of Cardium costatum Linnaeus, 1758, with the description of Cardium maxicostatum spec. nov. from tropical West Africa (Bivalvia, Cardiidae)

2007·2.1 MB·English

by  Poorten, Jan Johan Ter

BASTERIA, 71:57-69,2007
Notesontheidentity of CardiumcostatumLinnaeus, 1758,
withthedescription ofCardiummaxicostatumspec. nov.
fromtropical WestAfrica (Bivalvia, Cardiidae)
Jan+Johanter Poorten
Siriusstraat57, 1223AMHilversum,TheNetherlands;[email protected]
Abstract
Itisshown thatwhatis generallyconsidered asinglespecies, theGreatribbed cockle,Cardium
costatumLinnaeus, 1758, consistsoftwoclearly differentforms,tobeseparatedatspecieslevel.
Amongthe availablepossible type material ofC. costatum, whichisin agreementwithoneof
these forms,alectotypeis selected. Becausenoalternativenameis available forthe remaining
form,anewspeciesis heredescribed asC. maxicostatumspec. nov.
Key words:Bivalvia,Cardiidae,Cardium,systematics, lectotype,newspecies, WestAfrica.
INTRODUCTION
Nowadays, the majorityof taxonomists assign only two extantspecies to thegenus
Cardium(s.s.), viz. C.costatumLinnaeus, 1758(type species) andC1 . indicumLamarck,1819.
Bothspecies have alargely sympatric distributionalong theWestAfrican coastand are
morphologically easily separated fromeachother:shellsof the latter lacking the hollow
andpointed character of theribs, exhibiting an ornamentationof spines, gaping much
strongerposteriorly, withribs not interlocking along thecommissure,and having apart-
ly purple and lightbrownishcolour(Ghisotti, 1971).
Cardium costatumis alarge, well-knownandstriking bivalve witha unique ribmor-
phology. Because of its remarkableappearance,itis easily recognised. Below itwill be
demonstratedthattwomorphologically clearly differentformsaretobe distinguished, to
beseparated at species level. Taxonomistshave apparently overlooked theexistence of
thesedifferencesduringthepast twoand ahalfcenturies, probably as aresultofitsseem-
ingly obvious identificationdue toits characteristicspecialised shell morphology. In all
probability,thisisalsothemain causeforthelackof virtuallyany synonyms.
Thepurposeofthispaperis toelucidatethedifferencesbetweentheseforms, totreat
theavailablepossible typematerialandtowork outthetaxonomicconsequences.
Abbreviations:BMNH,TheNaturalHistoryMuseum,London,UnitedKingdom; LS,
Linnean Society of London, United Kingdom; RMNH, Nationaal Natuurhistorisch
Museum Naturalis, Leiden, TheNetherlands; TP, colln. J.J. ter Poorten, Hilversum, The
Netherlands; UU, MuseumofEvolution, Uppsala University, Uppsala, Sweden; ZMA,
Zoologisch MuseumAmsterdam,The Netherlands.
Fr. =fragment(s); h.=height; 1.=length; p.v. =paired valve(s); v.=valve;w=width.
58 BASTERIA,Vol. 71, No. 1-3,2007
Figs3-9. Cardium spec. 3-6,C. costatum; 3,5, lectotype, unknown provenance, collnLS, length72mm;4,
6,paralectotype,unknownprovenance, collnLS, length74 mm.7-8,C. maxicostatumspec.nov.,unknown
provenance, colln UU(Linnésammlingen,nr.1386),length91mm;9.HandwrittentagaccompanyingUU
samplenr. 1386.
TerPoorten:Cardium maxicostatum spec. Nov.fromtropical WestAfrica 59
Figs 10-13. C. maxicostatum spec. nov., holotype, CongoBrazzaville, PointeIndienne,from fisherman,
07.11.1972,collnZMA Moll.4.07.023,length117mm.
MATERIALANDMETHODS
The termflange is used forthesubstantial, continuousprojections on topoftheradi-
alribs, whichhavethe shape ofakeel.The termmedianpartis used in abroadsense for
thearea containing theribs thatconsistof ahollowsection and thatconsist oftwo parts,
viz. thecentral, broadbase(the actualrib)and thepointed flange. These ribs areconsid-
ered torepresentthemain ribs.
In somecases,theprojectionsofthemedianribsextendwellbeyond theshellmargin.
Fortheshelllength, theseextensionsareincludedin themeasurements whenfallingwith-
inthehorizontalaxis, measuredparalleltothehinge line.
60 BASTERIA,Vol. 71, No. 1-3,2007
In total75 samples havebeenstudied, consisting of 196specimens, originating from
LS,RMNH, UU, ZMA,and TP.
Only those references are incorporated with figures that could unequivocally be
attributedto one ofbothtaxa. In many cases, illustrationsand descriptions, especially
thoseofearlierworkers, were not accurate enough to enableacertainassignment toone
ofthetwodiscussed taxa.
THE IDENTITYOFCARDIUM COSTATUM
Cardiumcostatum Linnaeus, 1758,is widely known tobe characterisedby arelatively
large,ratherthinshell, whichisinflatedandnearly equilateral, withalimitednumberof
largeand hollowribs andawhite colourwithbrownareas intheintercostae.This corre-
sponds withLinnaeus'(1758: 678) original description: ‘C. testagibba aequivalvi: costis de-
fah's carinatisconcavis membranaceis'[shell gibbous, equivalve: withhigh,keeled,concave,
membranaceousribs]. However, withinthis general appearancetwo differentmorpho-
logicalforms, provisionally namedAandB, canbe detected.Nine differentiating charac-
ters are tabulatedbelow.
Although most charactersshow a certaindegree of variation- mainly theextent of
development of the anteriorriblets and the nature of thehinge plate - no intermediate
formswere found.Fig. 1shows oneofitsmost distinctivediagnosticcharacters:theshell
length ofbothtaxa plotted againsttheheight ofthehighestflange presentontheshell.In
mostcasesthisproved tobe situatedonthemostposterior mainrib.Atcomparable sizes,
theflange is muchlarger in formB (circa 1.75timescompared toformA,fig. 1);besides,
theshell attainsconsiderably larger dimensionsthanformA.Anotherclear differenceis
theribnumberonthemedianpartof theshell(fig.2),whichis clearly higherin formB.
Character FormA FormB
Length Up to circa 100mm Upto circa 130mm
Ribnumberonmedianpart 7-10ribs (mean 8.73,n=48) 9-13ribs (mean 10.56,n=55)
Posteriorpart Slightly to moderately Moderatelyto markedly
gaping gaping
Natureofribs on Moderately high flanges, Extremely highandslender
medianpart allof approximately same flanges,becoming much
height, upto4.5mm higherposteriorly, upto
12.5mm
Hinge plate Anteriorpartrathersmall, Anteriorpartratherbroad,
slightly curved long andstraight
Posteriorribs Welldeveloped, strong, Highlyflattened,strongly
thick, andtriangular, pal- developed, thinpalisade
isadepoor posteriorly
Posteriormargin Strongly digitatedand Serratedor weakly digitated
projecting
Anteriorriblets Most dorsally positioned Dorsalribletgenerally of
riblet generallymore aboutthesamestrength as
pronounced others
Shellresorption in interior Clearly presenton6-9 Clearlypresenton 4-7
interstices interstices
TerPoorten: Cardiummaxicostatumspec, nov.from tropical WestAfrica 61
Fig. 1. Scatter diagramshowingrelation shell length (horizontalaxis) and heightofthe largest flange
(vertical axis) forCardium costatum formA(greysquares, n=46)andB (blacksquares, n=134). Sizes
inmm;basedonmaterial fromRMNH,ZMAand TP.
Bothformsoccur sympatricpracticallythroughout theirdistributionrange.Giventhe
large amount ofsubstantialandratherconstantdifferencesinshellmorphology andsince
intermediateformsarelacking, separation ofbothforms atspecies levelis necessary.
Linnaeus' concise type description is not detailedenough to be attributedto either
formAorB.Moreover,thefigures Linnaeus(1758:678)isreferring to,viz.Colonna,1616
(fig.27),Rumphius, 1705(pi. 48fig.6), d'Argenville, 1742(pi.26 fig.a), andGualtieri,1742
(pi. 72fig. d)showalarge degreeofartisticfreedomand are thus consideredinadequate
tobeascribedtooneofbothformswithany degreeofaccuracy.
According to Dodge (1952: 54) "a correctly marked specimen" is present in the
Linnaeus collection.MmesK. Wayand A.MacLellan(BMNH)kindly provided mewith
photographs of thetwo valvesof C. costatum,presentatthe LinneanSociety ofLondon,
where Linnaeus' personal collectionis housed,aleft anda right one, length respectively
Fig.2.Stackedbargraphshowingrib numberonmedianpart
ofthe shell (horizontalaxis) ofform A (grey,n=48) and B
(black,n=55).Verticalaxis showingnumber ofshells meas-
ured; sizes in mm; based on material from BMNH, RMNH,
ZMAandTP.
62 BASTERIA,Vol. 71, No. 1-3,2007
Figs 14-21.Cardium spec.14-16, 19-20,C. costatum;14-15, 19-20,Angola,Luanda,bylocal fishermen,2005,
colln TP 2922,length81mm;16, Ghana,Greater Accra Province,Accra, floodmark, 14.xi.2003,leg.W.
Regter,collnTP 1654,length95mm.17-18,21,C. maxicostatumspec. nov.;17,Angola,collnTP444,length
97mm; 18, 21, paratype,Angola, Luanda District, Cacuaco, dredgedoffshore, insand/mudbottom,
depth15m, 1993, collnTP 898, length94mm.
TerPoorten: Cardium maxicostatumspec. Nov.fromtropical WestAfrica 63
72 and 74 mm (figs 3-6; Hylleberg, 2004: 843). The accompanying labelby S.P. Dance
states: "Hanley hasisolatedtwo unmatchedvalves.One is unmarkedthe other,inferior
valve is marked ‘C. costatum’ in pencil". Both are clearly in agreement with form A.
Linnaeusused tomark specimens in hispersonal collectionwiththenameorwithanum-
ber (Dodge, 1952). Only oneof the valves of the LS has a markedname in pencil, in a
handwriting clearlydifferentfromthatofLinnaeus.Nosupplementary valvesarepresent
inthecollectionoftheLinnean Society (personal communication,Mrs K. Way).
Mr.O. Israelsson(UU)kindly presented me withphotographs ofLinnaean material
ofthistaxonoriginating fromtheMuseum LudovicaeUlricae, deposited in hisinstitution
(Linnesamlingen, 1386)consisting of onecomplete specimen (figs 7-8), length 91 mm, in
agreement withformB. Itis unmarked,except for a printed “Cardium costatum” label,
glued on theexterior ofbothvalves. Thepresenceof this materialis in agreementwith
Linnaeus (1764), with C. costatum listedunder no. 31. Of the two accompanying hand-
writtenlabelsonementions“costatum”; theother"Mus. Car[o]l. XIII" (fig.9), suggesting
tooriginate fromtheSwedish/NorwegianKing CharlesXIII(1748-1818;alsonamedKarl
XIII, Carl XIIIand in Norway Carl II), thesecond sonofking AdolfFrederickofSweden
andLouisa UlricaofPrussia. Italso couldreferto the13"1editionofLinnaeus' Systema
Natura(Gmelin, 1791)and hisChristianname:"Carl"or"Carolus".
Dodge (1952) points outthatfrom1789to 1803Prof.OlausSwartzwas thecurator of
thecollection, thattheprintedlabelspasted onthe specimens arehisworkand thatthere
never hasexisted asingle labelin thecollectionpreparedby Linnaeus.Itisevidencedby
Linnaeus(1764: 483) thathemusthaveexamined aMuseumLudovicae UlricaeC. costa-
tum,and thespecified ribnumber(11-12 elevatedribs) fitswiththeUU specimen; there-
fore theabove cited specimen couldwellbethevery sameLinnaeushadin frontofhim
whenstudying thecollection.Itis possible thathe partlybased his 1758 description on
that particular specimen ashis manuscript oftheLouisaUlricacollectionwas completed
as early as1754(Dance, 1986).
Itcanbe concludedthatneithertheLinneanSociety valves,nor theUU specimen can
unambiguously beregarded asLinnaean.Atthe sametime it cannot be excluded atall
thatthevalves inthe LinneanSociety indeeddidbelong toLinnaeus'personal collection
and tohis studiedmaterial.Thereforethey shouldberegarded syntypical. Moreover,of
allshellsin thecollectiontheyuniquely fitthe1758 description.
Inordertostabilisethistaxon,alectotypehastobeselected.Fortheabovementioned
reasons itisadvisabletochooseaspecimen derivedfromLinnaeus'personal collectionat
theLS. Hencetheundamaged LS leftvalveis hereby selectedas lectotype ofC. costatum
(figs3, 5), theremainingunmatchedrightvalvebecoming paralectotype (figs4, 6).
When searching for availablenames intheliteratureitisevident thatthenumberof
possible synonyms is very limited.
Cardiumcostatum africanum Chemnitz, 1782 (pi. 15 figs 151-152) has 8 ribs on the
medianpartand is unmistakably in agreementwithform A.Besides, Chemnitz, 1782, is
not consistentlybinominaland rejected fornomenclatorialpurposes(Direction 1,ICZN).
Bruguière, 1789,whentreating C. costatum,only liststhisnameunderthesynonymyofiC.
costatum,whichdoesnot validateChemnitz'sname(ICZN, 1999,Article 11.5.2).
Cardium crenatocostatumBronn, 1831, isbased onfossil materialfromItalianorigin.
Thistaxonis synonymised withC.costatum byFischer-Piette(1977)andHylleberg (2004).
This viewcannotbe upheldbecauseBronn(1831) points outitscloseaffinitywiththefos-
silCardium hillanumJ. deC. Sowerby, 1813,a shellwhichis largely coveredby close-set
commarginal riblets, insharp contrast withtheposterior quarterthatis ornamented with
well developed radialribs. It is the typespecies of theMesozoic genus ProtocardiaVon
Beyrich, 1845,and known from the Cretaceous. The description of Bronn (1831), not
64 BASTERIA,Vol. 71, No. 1-3,2007
accompanied by afigure, mentions 'sulcis55-60', referring to theclose-set commarginal
riblets, whichhavea dense'crenated'appearance,henceitsname.
As noothernamesthatpossibly couldbelinkedtooneofthetaxa areavailable,itwill
be describedasnewbelow.
SYSTEMATICPART
CardiidaeLamarck, 1809
CardiinaeLamarck, 1809
CardiumLinnaeus,1758
Type species: Cardiumcostatum Linnaeus,1758
Cardiumcostatum Linnaeus,1758(figs3-6, 14-16, 19-20)
Cardium costatumLinnaeus, 1758:678,no.58; 1764: 483,no. 31; 1767: 1121,no. 73.Roux, 1828:fig. 9.
Nickles, 1950: 196, fig. 370. Knudsen & Hylleberg, 1999: 421-422, fig. 2. De Bruyne, 2003: 265.
Hylleberg,2004:843,toprowand 922toprow.
Cardium costatumafricanum Chemnitz,1782:156,pi.15figs 151-152[rejectedwork, ICZN]
Cardiumindicum Bruguiere,inBory deSt.-Vincent,1827:pi. 293 fig.la-c [notCardium indicumLamarck,
1819].
Typematerial. —Lectotypeinthe LinneanSociety collection (designatedabove),leftvalve,length72mm
(figs 3, 5). Type locality notspecified byLinnaeus (1758).AccordingtoLinnaeus (1767: 1121) "in M.
Africano".
Description. — Shellinflatedandnearly equilateral, broadly oval, largeandrelative-
ly thin-shelled,especially theintercostalspaces.Length 75-95.5mm.
Dorsalmarginnearly straight, antero-dorsalmargin gentlyrounded.Ventralmargin
serrated,internally exhibiting smalland narrowslits ofthehollowribs. Posteriormargin
strongly digitated,slightly tomoderately gaping, mainly causedby the digitated margin.
Ribimpressions pronounced andsharply delimitated, superficially developed onposteri-
or quarter. Anteriorslope: 4-6 close-set riblets, well marked, dorsal oneoften generally
much more pronounced. Medianpart: 7-10radialribs (mean8.73, n=48), interlocking,
consisting ofabroadbaseanda centralpart withapointedbutnarrow hollowflange, all
of them roughly similar sized. Ratio ribs/interstices on median part of the shell of
(sub)adult specimens circa2.5-3:1.Posteriorquarter: 5-6pronounced and solid ribs, tri-
angular incross-sectionand lackingthe pointed centralpart. Anteriorsideroundedand
inflated,becoming flattenedorevenslightly concave duringontogeny;posteriorsidever-
tical, overhanging, slightly concave andcarrying a weakly developed, tiny, irregular, cal-
careous palisade; normally only wellpreserved injuveniles upto afew centimetres.On
fullyadultspecimens, thispalisadebecomesmarginally muchmorepronounced andpro-
jecting.Finegrowth striaepresentonthewholeshell, especially wellvisiblein theinter-
stices.
Hinge platesmall, hinge withoneanterior lateral,twoposterior lateralandtwo car-
dinalteethinleft valve; two anterior lateral,one posteriorlateraland two large, project-
ing cardinalteethinright valve.Ligament short.
TerPoorten:Cardium maxicostatum spec. Nov.fromtropical WestAfrica 65
Exterior white, except for interstices onmedian part, which are rusty-brown pig-
mented, fadingtowardsontogeny.Interiorwhitewithcorresponding colouredrays on6-
9 intercostae whereshell resorption hastakenplace. Periostracum olive-green; thin, but
thicker nearthemargins.
Distribution.—WestAfricanfaunaprovince, ranging from Senegalto Angola(exclu-
sively basedon verifiedsamples).
Remarks. — Thelargest specimen observed originates from Ghana(1.95.5 mm, leg.
W.Regter, coll. TP,fig. 16). Although itis seemingly mostclosely related toC. costatum,
thesmallersizeand theprojecting digitationsoftheposterior marginalsorecallthemor-
phology ofBucardiumringens (Bruguiere, 1789).
Material examined. — SENEGAL, Kayar,beach, leg.G.C.Cadee, 3.xii.l976 (ZMA/2v.). GAMBIA,
leg. J. vanLeeuwen, 4-10.ii.2006 (TP2967/2v.);about 8 km SW. ofBakau, KotuBeach,leg. G. & A.
Wiepking, 26.xii.1994 (TP 2878/lv.); BrufutBeach-Tanji Bird Reserve creek, sandy beach, leg. S. van
Leeuwen,6.ii.2006(TP2914/1v.);TanjiCreek-Solifo Point(300mN. upto 3km S. ofTanji),sandybeach,
leg.S.vanLeeuwen,6.ii.2006(TP2915/lv.);Kotu Creek-Kololi,nearentranceBijiloForest,4km sandy
beach,leg.S. vanLeeuwen,6.ii.2006 (TP2916/3v.);Kotu Creek-Fajara, nearrock formation,leg.S.van
Leeuwen, 5.B.2006(TP2913/1v.);25km W.ofBanjul,Badala Park, sandybeach,4.L1998,leg.H.P.M.G.
Menkhorst (RMNH84617/lv.).IVORYCOAST,E. ofGrand Bassam,Kamoeriver mouth,beached,leg.
AJ.M.Leeuwenberg,7.xii.l958 (ZMA/3v.); Kamoerivermouth,leg.JJ.F.E.deWilde,ix.1956(ZMA/lv.).
GHANA, VoltaProvince,4km N.ofAnjanui,onsandbankinlagoonnearthe oceansurf,leg.W.Regter,
31.X.2005(TP2797/1v.);VoltaProvince, Srogbar,fromfisherman, leg.W.Regter,16.xi.2004(TP1942/3v.);
Volta Province,BigAda,onsandbanksinrivermouth,leg.E.Makken, 8.X.1992 (ZMA/3v.);Greater Accra
Province, Accra, highlyexposed,steepbeachwith coarsesand andpebbles,floodmark,leg.W.Regter,
14.xi.2003(TP 1654/5v.);local fishermen (TP2921/lp.v.). NIGERIA, Lagos,leg.L. dePriester(ZMA/3fr.);
Lagos,VictoriaIsl.,Barbeach,leg.W.Bergmans,27.viii.1976 (ZMA/lv.);Niger delta,leg.J.P.vanderSluis
(RMNH/lv.);SE. ofPort Harcourt, Opobobeach (RMNH,coll. Keij/lv.). CAMEROON, Kribibeach,leg.
Mr. & Mrs. W.J.J.O. de Wilde-Duyfjes (RMNH/lv.).EQUATORIAL GUINEA, Rio Mundi,leg.M.v.d.
Goes van Naters, i.1969 (RMNH, coll. Timmermans/lp.v.). CONGO BRAZZAVILLE (RMNH/lv.);
(ZMA/lv.);Pointe Noire,beach, 19.xii.1972(ZMA,coll. Bergmans/lv.).ANGOLA,Luanda,leg.A.J.P.v.d.
Graaf,vi.1955(ZMA,coll. Gravestein/3v.);Luanda area, leg.A.P.v.d.Graaf (ZMA/lp.v.); Luanda area,
leg.A.v.d.Graaf, 1955-1960(ZMA,coll. Niehe/2v.;coll.VanPel/lp.v.);Luanda,localfishermennets, 2005
(TP2922/lp.v.). Unknow provenance: BMNH,LS coll./2v.
Cardiummaxicostatumspec.nov.(figs 7-8, 10-13, 17-18,21)
Pectunculus 2.'Le Kaman',Adanson,1757:243-244,pi. 18,G.VI,fig. 2 [notavailable].
Cardium costatumLinnaeus, 1758; Wood,1815:231,pi. 56fig. 1;1825:pi.5fig.34.Reeve,1844:pi.2 fig. 11.
Chenu,1862: 107,figs 483-484. Thiele, 1934:880-881,fig. 832.Popov, 1977: 42,pi. 1figs1-2. Keen,
1980:pi. 4fig. 2.Abbott&Dance, 1982: 326,fig.Bernard,1984: 114, pi. 48fig.a.Gofas etal., 1985:
114,pi. 48 fig.a.Savazzi,1985:304,fig.7a-d. Voskuil &Onverwagt,1989:55-56,fig. 1.1.01,pi. 1fig.
1.Matsukumaetal., 1991:pi. 145fig. 10.Rodriguez&Sanchez, 1997: 251.Schneider,2002:figs6a,
11a,12a,18a.Ardovini&Cossignani, 2004: 279.Savazzi &Salgeback, 2004: figs la-h,2a-g.
Description. — Shellinflatedand nearlyequilateral, broadly oval, largeandrelative-
ly thin-shelled,especially theintercostalspaces.Length 100-130 mm. Anterior slope: 4-8
close-setriblets, weakly developed, insomecasesofunequalstrength, sometimesincreas-
ingly developedtowardsdorsalmargin.Medianpart:9-13radialribs (mean10.56,n=55),
interlocking, eachconsisting of abroadbase and acentralpart with anextremely high,
66 BASTERIA, Vol. 71,No. 1-3,2007
slenderand pointed hollowedflange, theposterior onesbecoming gradually larger, with
a centralpart upto circa 12mmhigh(fig. 1:formB). Ratioribs/interstices onmedianpart
of theshellof(sub)adultspecimens circa 1.75-2:1.Posteriorquarter: 5-6broad, highlyflat-
tenedribs, posteriorly sculptured withastrongly developed, erectand irregular calcare-
ous palisade. Dorsal margin straight, generally with sharp and abrupt angulation on
antero-dorsalcorner.Ventralmarginserrated,internallyexhibiting largeandwideslitsof
thehollowribs. Posteriormarginserratedor slightly digitated, clearlygaping. Ribimpres-
sionspronounced andsharply delimitated,butinvisibleonposteriorquarter.Finegrowth
striaepresentonthewholeshell, especially wellvisibleintheinterstices.
Hinge platebroad, hinge withoneanteriorlateral, two posteriorlateralandtwo car-
dinalteethin left valve; twoanterior lateral, oneposteriorlateraland two large, project-
ing cardinalteethin right valve.Ligament short.
Exterior white, except for interstices on medianpart, which are rusty-brown pig-
mented,fading towardsontogeny.Interior whitewith corresponding colouredrays on 4-
7 intercostaewhereshellresorption has takenplace. Periostracum olive-green coloured;
thin,howeverthickernearthemargins.
Holotype. — Congo Brazzavile, PointeIndienne,from fisherman, 07.11.1972.ZMA
Moll.4.07.023(figs 10-13); 1.117.0mm;h.109.7mm;w.96.1 mm;h.largest flange 10.8mm.
Distribution. — West African fauna province, ranging from Mauritania to Angola
(exclusively basedonverifiedsamples).
Etymology. — FromtheLatinwords maximus(maximum)andcostae(ribs), referring
to thelarge size and thepronounced flanges on topof theribs, bothaspects much more
prominent than inC.costatum.
Remarks. — This species appears tobemore common thanthepreceding one: the
vast majorityof identifiableillustrationsin theliterature refersto thisspecies and it is
more often encounteredin collections. However, there is no indication at all thatthis
relatestoashallowerbathymetric range.
In worn valves, the angulated edge of the antero-dorsalmargin isoften erodedor
partlybrokenoff, similartowhatis seeninC. costatum.
The largest specimen observed is from unspecified WestAfrican origin(length 130
mm;coll.ZMA).
Type seriesand othermaterial examined. — MAURITANIA,offBanc d'Arguin,20°00'N17°10'W,
depth24m, 14.vi.1988,Tyro Mauritania-II Exp. 1988, st.MAU 076 (RMNH13270/lv.,paratype); ditto,
20°00'N 17°12'W, 28 m, muddy sand, 13.vi.1988, Tyro Mauritania-II Exp. 1988, st. MAU 067
(RMNH13268/3v.,paratypes); ditto,20°01'N 17°09'W,22m, 14.vi.1988,TyroMauritania-IIExp. 1988,st.
MAU. 075 (RMNH.13269/lp.v.,lv.,paratypes);SENEGAL (TP72/lp.v.); Kayar,beach,leg. G.C.Cadee,
3.xii.l976 (ZMA/13v.);Rufisque, leg.G.C. Cadee,3.xii.l976 (ZMA/2v.);Kafountine,atlow tideonsandy
beach,leg.H. van Oosten,iv.1995 (TP 556/2v.);Casamance,dredgedonsandybottom, 10-20 m (ZMA
Moll. 4.07.025,coll. Koekkoek/lp.v., paratype); Casamance,offshore, 10-20m, xi.1990 (TP2877/2p.v.);
ditto, 1992 (TP 147/lp.v.); N'Gor, 1987 (TP 2876/lp.v.); Rufisque (ZMA Moll. 4.vii.024, ex coll.
Dautzenberg,coll. DePriester/lp.v., paratype);M'Bao,beach, 20.08.1966(ZMA,coll.Harmon/2v.).GAM-
BIA, about8kmSW. ofBakau,KotuBeach,leg.G.&A.Wiepking,26.xii.1994 (TP2880/2v.);BrufutBeach-
TanjiBird Reserve creek, sandybeach, leg.S. vanLeeuwen,6.ii.2006 (TP2918/5v.); Tanji Creek-Solifo
Point(300mN.upto3km S. ofTanji),sandybeach,leg.S.vanLeeuwen,6.ii.2006 (TP2946/7v.);Sanyang-
3kmN. ofSanyang,sandybeach,leg.S.vanLeeuwen,8.ii.2006(TP2917/25v.);KotuCreek-Kololi,near
entranceBijiloForest, 4kmsandybeach,leg.S.vanLeeuwen,6.ii.2006 (TP2916/13v.);Kotu Creek-Fajara,
nearrock formation,leg.S.vanLeeuwen,5.ii.2006(TP2919/9v.);25kmW.ofBanjul,BadalaPark,sandy
beach,4.i.l998,leg.H.P.M.G.Menkhorst(RMNF184617/5v.).IVORYCOAST,E.ofGrandBassam,Kamoe
rivermouth,beached,leg.A.J.M.Leeuwenberg,7.xii.l958 (ZMA/lv.);Kamoerivermouth,leg.J.J.F.E.de