Acanthocardia sliggersi spec. nov. (Bivalvia, Cardiidae) from the Late Pliocene and Early Pleistocene of The Netherlands

2006·1.1 MB·English

by  Moerdijk, P W

BASTERIA, 70: 89-96,2006
Acanthocardiasliggersi spec.nov. (Bivalvia, Cardiidae)from theLatePliocene
andEarly Pleistoceneof TheNetherlands
P.W.Moerdijk
Kingstraat14,NL4336 LGMiddelburg, TheNetherlands;[email protected]
&]J.J. ter Poorten
Siriusstraat57,NL1223AM Hilversum,The Netherlands;[email protected]
AnewspeciesofAcanthocardia,A.sliggersi, is described from Late Pliocene (Piacenzian)and
EarlyPleistocene (Gelasian) depositsofthe North SeaBasin.The speciesis closely related to
Acanthocardia echinata(Pliocene-Recent,north-easternAtlanticregion).Apossiblerecentoccur-
renceofA.sliggersiinthe Russian arcticcannotbeexcluded.
Key words: Bivalvia,Cardiidae,Acanthocardia, taxonomy, newspecies, Pliocene,Pleistocene,
NorthSea Basin,The Netherlands.
INTRODUCTION
During an inventory of thefossil shellsfrom beachesand estuaries of Zeelandour
attentionwas drawn to shells of an Acanthocardia species washed ashore at Domburg
(Zeeland, TheNetherlands), originally identifiedas A.echinata(Linnaeus,1758).Because
oftheiratypicalshellmorphology,wethoroughly compared themwiththeRecentA.echi-
nata andalsowiththerelatedA.paucicostata (Sowerby, 1841).We describethefossilshells
asA.sliggersi spec. nov.Thenew speciesappearstobeendemicto thesouthernNorthSea
Basin during theLate Pliocene(Piacenzian)and Early Pleistocene(Gelasian).
Abbreviations:BMNH,BritishMuseum(NaturalHistory),London,UnitedKingdom;
KZGW, Koninklijk Zeeuwsch Genootschap der Wetenschappen, Middelburg, The
Netherlands; RGM, National Museum of Natural History, Naturalis, Department of
Palaeontology (Cainozoic Mollusca) (formerly Rijksmuseum van Geologie en
Mineralogie), Leiden, The Netherlands; TNO-NITG, Netherlands Instituteof Applied
Geosciences, Utrecht, The Netherlands; ZMA, Zoological Museum, University of
Amsterdam, Amsterdam, The Netherlands. Additional abbreviations: H, height; L,
length; LV, leftvalve; RV,rightvalve.
90 BASTERIA,Vol. 70, No. 1-3,2006
SYSTEMATICS
FamilyCardiidaeLamarck, 1809
Subfamily CardiinaeLamarck, 1809
AcanthocardiaGray, 1851.
Type species (designated by Stoliczka, 1870: 207):CardiumaculeatumLinnaeus,1767.
Acanthocardiasliggersi spec.nov.(figs 1-3, 5)
Cardium echinatum Linnaeus;Wood,1853(?): 152,pi. 14fig. 3 a-b;1882: 12;Heering,1950: 117,pi. 10figs
23,(24), 25-26.
Type material.- Holotype:RGM 456319 (formerly NITGcollection), rightvalve(RV),
Maassluis, Zuid-Holland, The Netherlands,borehole37B25, 112-115 m below surface,
MaassluisFormation,Gelasian(figured inHeering, 1950:117,pi. 10figs 25-26,herefigs 1-
2).
Paratypes: RGM 456320(formerly NITG collection),juvenile valve(LV), Oudewater,
Utrecht, TheNetherlands,borehole38B26,154-158mbelowsurface,MaassluisFormation,
Gelasian(figured in Heering, 1950:pi. 10 figs 23-24);RGM 456321,Domburg, Zeeland,
TheNetherlands, 14valves, washedashoreonbeachbetweenDomburg and Westkapelse
zeedijk, presumably derived from Maassluis Formation deposits (Gelasian), leg. M.I.
Gerhardt(fig.3,5); KZGW4263,1valve, samelocality, leg. P.W.Moerdijk, 13.iv.2003;ZMA
4.06.002, 1 valve, north-westbeachof Walcheren,Zeeland,TheNetherlands,presumably
derivedfromMaassluis Formation deposits (Gelasian), leg. W. Kimpe, 28.viii.1935.
Othermaterial: Mr. T. Meijer(formerlyTNO-NITG) and mr. F.P.Wesselingh(NationalMuseum of
Natural History, Naturalis)listedA.sliggersifromboring-samplesintheNITG-resp.RGM-collection and
in internalreportsonboringsin theDutchsubsoil.Given aresubsequently,boringidentification,boring
name, boring intervals (depth in metres below OD), age ofsample,source(CI,Collection NITG; C2,
Collection RGM;Rl,InternalNITGreport;R2,Internal RGMreport;P,publishedpaper),originalidenti-
ficationofthe sample,publicationand remarks.
05A84,WestTerschelling,344.70-346.20;359.90-361.70,EarlyPleistocene,Rl, asA.‘echinata ’,erod-
ed; 10C157,Breezanddijk, Wonseradeel, 316.00-320.00,Early Pleistocene, CI, Rl,as A.echinata, frag-
ments; 14E110,Hippolyteshoef, 320.00-321.00,Early Pleistocene, CI, asA. ‘echinata’,eroded; 19E101,
Sijbekarspel, 244.00-245.00; 317.00-318.00; 359.00-360.00; 362.00-363.00; 378.00-379.00; 379.00-380.00;
380.00-381.00;381.00-382.00;382.00-383.00;392.00-393.00;395.00-396.00,Early Pleistocene,Rl,A. ‘echina-
ta’,fragments; 19E101,Sijbekarspel,*378.00-379.00;379.00-380.00,Early Pleistocene, CI,asA. ‘echinata’,
well preserved; 19E101,Sijbekarspel, 419.00-420.00,Late Pliocene, CI, asA. ‘echinata’,well preserved;
Figs 1-6. Acanthocardia spec. 1-3, 5, A. sliggersi spec. nov.; 1-2,holotype, Maassluis, province ofZuid-
Holland,TheNetherlands, 112-115m below surface,RGM(NITG colln)456319,length40.9mm;3,5,
paratype,beach between Domburg and Westkapelse zeedijk,province ofZeeland,The Netherlands,
derivedfromprobablyEarlyPleistocene deposits,leg.M.I.Gerhardt,RGM456320,length41.1 mm.4,A.
echinata,beachofSchiermonnikoog,province ofFriesland,The Netherlands,24.viii.1999,Holocene-Late
Pleistocene deposits,leg.andcoll. J.J.terPoorten,NL1406,length38.7mm. 6,A.paucicostata,Amsterdam,
IJburg, raised site with sediments originating from Lake IJsselmeer, province of N. Holland, The
Netherlands,Eemiandeposits,leg.andcoll.J.J.ter Poorten,NL2096, length36.5mm. Photographs:figs
1-3,F.P.Wesselingh,RGM; 4-6, J.J.ter Poorten.
Moerdijk &terPoorten: Acanthocardiasliggersi spec. Nov.fromtheNetherlands 91
92 BASTERIA, Vol. 70,No. 1-3,2006
21A38,Schokland,229.40, Early Pleistocene, CI, as A. echinata, well preserved; Schokland,269/144?,
depth?,CI,asC.edule,referred toinHeering,1950,stronglyeroded;26D5,Eemnes,219.25-223.75,Early
Pleistocene,Rl,asA.echinata,;26D42,Zuid Flevoland,270.00-271.00;328.00-329.00;352.00-353.00,Early
Pleistocene,Rl, asA. ‘echinata’;26F1,Harderwijk, 313.73-315.90 (layer90),Early Pleistocene, CI,asA.
echinata,well preserved;27D53,Twello,202.00-203.00,LatePliocene,Rl,asA.echinata;27G35,Deventer,
123.40-127.40,Late Pliocene,Rl,asA.echinata;28C127,Espelo,65.20-66.50,Late Pliocene,Rl,asA.echi-
nata;30F470,Noordwijk,148.25-149.55;156.75-157.75;212.75-213.75;213.75-214.75;214.75-215.75;215.75-
216.75;216.75-217.75;271.75-272.75;303.10-304.10;304.10-305.10,Early Pleistocene, Rl, asA. sliggers,;
30G34,DenHaag,Drinkwaterleiding,Bor.0,135.04-146.68,EarlyPleistocene,CI, asA.echinata,referred
toinHeering, 1950, well preserved; 31G147,De Meern,245.00-246.00;265.00-266.00,Early Pleistocene,
Rl, as A. echinata; 32A323, Hilversum De Schans, 202.00-203.00;219.00-220.00; 220.00-221.00;223.00-
224.00; 224.00-225.00; 226.00-227.00; 227.00-228.00; 231.00-232.00; 232.00-233.00; 233.00-234.00, Early
Pleistocene,Rl,asA.echinata;32D114,Austerlitz,151.45-154.50,EarlyPleistocene,CI,Rl,asA.echinata,
well preserved; 32E74,Barneveld-I (Olieboring),250.00-260.00,,CI,Rl,asA.echinata; 37B25, Maassluis,
109.00-115.00,Early Pleistocene,CI,P,asC. edule,referred toinHeering,1950, stronglyeroded;37B25,
Maassluis, 161.41-168.45,Early Pleistocene, CI, P, asA. hostei, referred to in Heering, 1950; 37D134,
Brielle,127.00-143.00; 158.00; 166.00; 243.00, EarlyPleistocene,C2, R2,asA.echinata;38B26,Oudewater,
154.00-158.00,Early Pleistocene, CI,Rl, P,asA.echinata, referred to inHeering, 1950, well preserved;
38C385,Hendrik Ido Ambacht, 127.00-128.00;144.00-145.00;159.00-160.00,Early Pleistocene, Rl,asA.
‘echinata,;38E225, Benschop, 172.00-173.00,EarlyPleistocene,CI,asA.sliggersi,well preserved fragment
ofa non-adult specimen;38H178, Asperen, 146.00-147.00,Early Pleistocene, CI, Rl, as A. ‘echinata’;
39H25, Druten-V,76.50-83.25 (layers 62-68), Late Pliocene,CI,as A.echinata; Haamstede, 54.00-55.50,
Early Pleistocene, CI, Rl; Schouwen,?, "Fauna 3", CI, as C. edule, strongly leached; Schouwen, ?,
"Oudere Zone", CI, as C. edule,strongly eroded; 42G22, Schelphoek, 54.00-57.00;84.00-85.50,Early
Pleistocene,C2,R2,asC.echitiatum;42G40,Colijnsplaat,63.50-67.00,Early Pleistocene,C2,R2, asC. echi-
natum; ?42H20, Ouwerkerk,70.50-71.50;77.50-82.50,Early Pleistocene, C2, R2, as C.echinatum;43A8,
Sommelsdijk, 63.50-63.80,Early Pleistocene, CI,Rl, as C. edule, strongly eroded; 43A8, Sommelsdijk,
63.50-85.20,EarlyPleistocene,CI,Rl,as C.edule,stronglyeroded;43A8, Sommelsdijk,112.30-131.20, CI,
Rl,as C.edule,well preserved; 43A8,Sommelsdijk, 112.30-143.00,CI, Rl, asC. edule,stronglyeroded;
43A8,Sommelsdijk, ?,CI,Rl,as C.edule,stronglyeroded,complete,adultspecimen;43A46,Dirksland,
86.00-98.00;121.00-125.00,Early Pleistocene, C2,R2, asC. echinatum; Beers,Proefbor. 53 (former ID:
571/1),40.00-74.50,?,C1,asC.edule,strongly eroded; 44A155or44B10, Biesbosch,Dubbeldam,wellIIIor
VIII,?,?,CI,P,as C.echinatum,referredtoinHeering1950,well preserved non-adult specimen.
Diagnosis. - An oval, subequilateral cardioidshell of up to about40 mm in length
with ca. 21 triangular,radialribs which areabouttwice as broadastheir interstices.On
the ribs a knobbed keel is present. The shell surfaceis ornamentedwith fine,irregular,
commarginal striae.
Description. - Theholotype (figs 1-2)is asolid, ratherinflatedrightvalve. The shell
hasabroadly ovaloutlineandisslightly inequilateral.Thelengthis exceeding theheight.
Theumbonesarelocatedbeforethemidlineandareclearly prosogyrate.Theshellis orna-
mentedwithabout20primary radialribs (range 19-23,average21)thathavealowtrian-
gular crossprofile ontheanterior andposterior quarter.Thetriangularribs becomemore
prominent onthemiddleregion oftheshell.Ontheanterior and medianpart theribs are
twice as broad as the interstices. On theposterior quarter they are weakly developed,
more closely set, with one tiny secondary riblet. The rib sculpture - only slightly pre-
servednearthemargins -consistsofanirregular, thinridge, withtiny,bluntandcloseset
nodules. The shell-surface shows a delicate, undulating commarginal pattern, that
includes theflanksof the ribs. Thegrowth-stages are clear.Thehinge isratherstrongly
Moerdijk & terPoorten:Acanthocardiasliggersispec. Nov.fromtheNetherlands 93
developed. Theright valvehastwoequally sized cardinalteeth; two anterior lateralteeth
and one posterior; the left valve (paratypes) has two cardinalteethof similar size; one
anteriorand oneposterior lateraltooth.Thelength ofnymph is ca.2/3 of the posterior
dorsal margin. The margins have deep crenulations; the furrows arenot extending far
inside the shell, developing into slight elevations and forming riblets towards the
umbonalcavity. The adductormuscle scars aresomewhatdepressed.
Variability. - Theshellmorphology seemstoberatherconstant. Theintraspecificvari-
ationin thestudiedmaterialis mainly relatedto achange inthecross-section of theribs
duringontogeny:in adultspecimens theribs are triangular, whereasinjuveniles theribs
generally exhibitatrapezoid shape. In thisrespectjuveniles of A.sliggersi closely resem-
blethoseof A.echinata,whichillustratestheircloserelationship. In well-preserved speci-
mens the rib sculpture extends more towards the top, forming a continuouspapillated
ridge with,however,theumboinvariably wornoff.
Dimensions(mm). — L H semidiameter ribnumber
RGM456319(holotype, figs1-2 40.9 37.0 13.7 20
RGM456320(paratype) 19.3 17.3 6.8 19
RGM456321(paratype) 41.0 38.5 14.4 22
RGM456321(paratype, figs3,5) 41.1 37.3 15.2 20
KZGW4263 (paratype) 38.0 35.2 13.1 21
ZMA4.06.002(paratype) 39.6 37.5 14.2 22
Derivatio nominis. - Named after Bert Sliggers, former palaeontologist at the
NationalGeological Survey ofThe Netherlands, forhisrecognition of thisAcanthocardia
as anundescribedtaxon.
Differentiation.-Acanthocardia sliggersi issimilartoA.echinata.Itdiffersmainlybyits
triangular insteadof quadrangular ribs, lacking a central furrow. Relatedto thewidthof
theinterstices, theribs arerelativelybroader thanin A.echinata.Besides, it differsby its
rib ornamentation whichis more crowded, muchless pronounced and of aless variable
nature. Its concentric, secondary ornamentation is more delicateand densely placed. On
average,A. sliggersi is smaller, reaching amaximum ofabout 45mm, whereasthemaxi-
mumlengthofA.echinataisabout75 mm.In somecharactersthenewspecies isquitesim-
ilar toA.paucicostata (Sowerby, 1841),butthelatteris decidedly morefragile; itsribs are
lessin numberand ofamoreflattenedtriangular shape. Acomparison betweenthethree
species is given in table 1.
Distribution.- Late Pliocene(Piacenzian, Reuverian, mollusc-zone Mol CofSpaink,
1975)andEarly Pleistocene(Gelasian, Praetiglian-Tiglian, mollusc-zones MolAand Mol
B of Spaink, 1975) of the southern North Sea Basin (we here refer to the Pliocene-
Pleistoceneboundary atca2.6Ma, followingsuggestions outlinedin Gibbardetal.,2005).
The species is fairly common in theEarly PleistoceneDutch MaassluisFormation.Apart
fromtheDutchrecords, thisspecies isknown fromtheRedCragofSuttonandFelixstowe
(Suffolk, GreatBritain, see discussion below). Both deposits belong to the Red Crag of
Newbourn (Harmer, 1914, 1920), which can be correlated to part of the Dutch Early
Pleistocene(which is named'Amstelien'by Harmer, 1896) deposits. The species is not
knownoutsidetheNorthSeaBasin.
94 BASTERIA,Vol. 70, No. 1-3,2006
Table 1.Comparisonbetween the specific characters ofAcanthocardia echinata, A.sliggersi andA.pauci-
costata.
AA..eecchhiinnaattaa AA..sslliiggggeerrssii AA..ppaauucciiccoossttaattaa
SSoolliiddiittyy ssoolliidd ssoolliidd rraatthheerrtthhiinn--sshheelllleedd
OOuuttlliinnee oovvaall oovvaall oovvaall,,ssoommeettiimmeessppoosstteerriioorrllyy
sslliigghhttllyyeelloonnggaatteedd
DDiimmeennssiioonnss lleennggtthh ttooccaa..7755mmmm lleennggtthhttooccaa..4455mmmm lleennggtthhttooccaa..4455mmmm
AAmmoouunnttooffrriibbss((aavveerraaggee)) 1188--2222((2211)) 1199--2233((2211)) 1144--1188((1177))
SShhaappeeooffrriibbss wweellll--ddeevveellooppeedd,, qquuaaddrraanngguullaarr wweellll--ddeevveellooppeedd,, ppooiinntteedd,, llooww,,ffllaatttteenneeddttrriiaanngguullaarr
oorrsslliigghhttllyyttrraappeezzooiidd,,wwiitthhaa ttrriiaanngguullaarr
cceennttrraallggrroooovvee
RRiibboorrnnaammeenntt cceennttrraallggrroooovvee,,wwiitthhrraatthheerrllaarrggee,, tthhiinnrriiddggee//ccoorrdd,, oorrnnaammeenntteedd rriiddggeewwiitthhttiinnyybblluunnttnnoodduulleess
ddiissttaannttllyyppllaacceedd ssppoooonnoorrccuusspp wwiitthhttiinnyy,,ddeennsseellyyppllaacceedd,, oorrssppiinneessoorr((aanntteerriioorrllyy))ssppoooonn
lliikkeessppiinneessccoonnnneecctteeddttooeeaacchh bblluunnttnnoodduulleess lliikkeessppiinneess
ootthheerraatttthheeiirrbbaassee,,ssppiinneessoofftteenn
ccuurrvveedd ttoowwaarrddsstthheeppoosstteerriioorreenndd
RRiibbss--iinntteerrssttiicceess rriibbssccaa..11--11..55xxtthheeiinntteerrssttiicceess rriibbssccaa..22xxtthheeiinntteerrssttiicceess rriibbssccaa..22xxtthheeiinntteerrssttiicceess
RRaaddiiaalloorrnnaammeennttoonn aallwwaayysswwiitthhaann iirrrreegguullaarrrriibblleett aallwwaayysswwiitthhaanniirrrreegguullaarrrriibblleett ssoommeettiimmeesswwiitthhaanniirrrreegguullaarrrriibblleett
ppoosstteerriioorrppaarrttooffsshheellll
CCoommmmaarrggiinnaall oorrnnaammeenntt qquuiitteeccooaarrssee,,mmoorreessoooonntthheerriibbss ffiinnee ffiinnee,,ooccccaassiioonnaallnneeaarrllyyssmmooootthh
IInntteerrnnaallrreefflleeccttiioonnoofftthhee iinnmmaajjoorriittyyvviissiibblleettoowwaarrddsstthhee ddeevveellooppiinnggiinnttoosslliigghhtteelleevvaattiioonnss aallwwaayyssvviissiibblleettoowwaarrddsstthheeuummbboo
rriibbss uummbboo ttoowwaarrddsstthheeuummbboo
Discussion. - WithinAcanthocardia, the shape of the ribs is a constant feature, thus
forming arelevantdiagnostic marker, whereasthenature of therib ornamentationmay
vary to a certain degree. Thereforewe conclude that A. sliggersi represents a separate
taxon. ShellsidentifiedasA. echinatafromthePlioceneof Iceland(Mactra-horizon: >2.55
Ma,theagegivenforthetopoftheoverlying Serripes-horizonbyBuchardt&Simonarson,
2003) and illustratedby Gladenkovet al. (1980) show clearly quadrangular ribs with a
central furrow and obviously belong to A. echinata.Theoccurrence of A. echinata earlier
thanor contemporarily withA.sliggersi is anotherargumentto judge thelatter different
atspecific level.Acanthocardia sliggersi probably evolvedfromA. echinata.We canassume
thatthedrasticcooling downofNorth-westernEurope during theLatePlioceneandEarly
Pleistocenecausedthegeographical isolationthataccommodatedthe development ofA.
sliggersi.
Wood (1882), discussing ashellof A. echinatafromthe RedCrag of Sutton(Suffolk,
GreatBritain), madethe observation, that"TheCrag shellhastriangular ribs(unlike the
commonrecent species, onwhichthe ribs are quadrate)". Thisis in accordance with A.
sliggersi. Theshellillustratedby Wood(1853, pi. 14 fig.3a-b) is deposited in BMNH,but
unfortunatelywasnotavailableforloan.However,relyingontheillustrationand descrip-
tionwe canassume thatitbelongs to thenew species underdiscussion.InWood'sview
(Wood, 1882:12) his shell"...belongs probably to thevariety calledovata by Dr.Jeffreys
...". Jeffreys (1863:271)introducedCardiumechinatumvar.ovata,basedonmaterialwitha
length ofless than4 mm.Themainmentionedfeature distinguishing thevar. ovata from
typicalA. echinata("ribs sharp") mayfitwithintheconchological charactersofA. sligger-
si.Jeffreys'namehasremainedenigmaticeversinceitsintroduction:asfar asweknow it
hasonly oncebeencitedin literature(Wood, 1882:12).Furthermoreitis notaccompanied
Moerdijk & ter Poorten:Acanthocardiasliggersi spec. Nov.from theNetherlands 95
by anillustration, nor any referencetoone.No typelocality hasbeen designatedand no
typematerialcouldbefound (Waren, 1980).Cardium echinatumvar. ovatais therefore con-
,
sideredbotha nomendubiumandanomenoblitum.
Acanthocardiasliggersi is found in well samples in The NetherlandsofLate Pliocene
(Piacenzian) and Early Pleistocene(Gelasian) age, where it occurs in boreal molluscan
assemblages (Spaink, 1975)oftheMaassluisFormation.Inbeach-samples fromDomburg,
shellsofA.sliggersi are always totallyfossilised (recrystallised) and ofa grey-blue,some-
times brown or white colour. As faras cardiids are concerned, material from Serripes
groenlandicus (Mohr, 1786) and Ciliatocardiumciliatum (Fabricius, 1780), both having a
Recent panarctic and highboreal distribution, shows thesame kindofpreservation and
colour.
The shellsurfaceoftheexamined materialof A.sliggersi is invariably partly decorti-
cated,especially in theumbonalregion. Next tothe margins, theshellas arule is intact,
andbetween umboand ventral margin some commarginal ridges and/or zones of the
outershelllayer areusually preserved. Similardecorticatedzones arepresentintwofresh
specimens of A. echinata, trawled offIceland from a depth ofabout 120 m (coll. J.J. ter
Poorten). Corrosionoftheumbonalregion duringthelifespanoftheanimalis acommon
phenomenon in (sub)arcticbivalves. Thisis causedby therelatively highHCC>3-concen-
trationof cold, (sub)arctic waters,which dissolves the calcium carbonateof thebivalve
shell and especially affects the aragonite components(Vermeij, 1978). We suspect that
theseaspects are involvedinthischaracterofA. sliggersi.
Some cardiidspecies commonly suffer loss of the outer shell-layer during the life
sLpanof taheanimeal.Forivnstancei,thcishasbaeenprorveddforthePilioucene mdecor-
ticatum (Wood, 1849). However, thepresence of decorticated Laevicardium-specimens in
warm-temperate assemblages in Piacenzian deposits in the southern North Sea Basin,
indicatesthatdecorticationnotnecessarily needstoresultfrom coldwater temperatures.
Acanthocardia sliggersi has not been found in fosilliferous Pleistocene deposits
youngerthenca 1.8Ma, thatarerare intheNorthSeaBasinanyway. However,wecannot
exclude that the species still lives in the Russian Arctic. A.I. Kafanov (pers. comm.,
06.2002) statesthatA. echinata livessympatric withCiliatocardiumciliatumin theBarents
Sea.Theillustrationsofaspecimen by Filatova(1948:pi. 109fig.4)ofashellidentifiedas
A. echinata, probably originating from theBarents Sea, might in factrefer toA. sliggersi.
Theribs looktriangular inshape, withouta centralgrooveandtherib-ornamentisnotori-
entatedto theposterior sideofthe shellas in themajorityof A.echinata.Theline draw-
ings donot provide absolutecertainty. Despite various efforts, we have beenunableto
retrace thematerial.
ACKNOWLEDGEMENTS
Thanks are due to Mr T. Meijer (National Museumof Natural History, Naturalis,
Leiden,formerly NITG-TNO,Utrecht) forproviding theinformationontheoccurrenceof
A.sliggersi intheDutchsub-soiland fordiscussionand literatureonstratigraphy; to Mr
F.P. Wesselingh (National Museum of Natural History, Naturalis, Department of
Palaeontology, Leiden) forcriticallyreading themanuscript andforhishelpandsupport
in many ways; to Mr R.G.M. Moolenbeek and Mr A.N. van der Bijl (both ZMA,
Amsterdam) for access to the collection; to MrsK. Way and Mr J. Todd (both BMNH,
London,UK),MrA.I.Kafanov(Institute ofMarine Biology, Vladivostok,Russia), Mr.B.I.
Sirenko and MrA.Voronkov (Zoological Instituteof Russian Academy of Sciences, St.
Petersburg, Russia); MrW.Vader(Tromso Museum,Tromso,Norway) forinformation.
96 BASTERIA,Vol. 70, No. 1-3, 2006
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