Two subspecies of Unio crassus Philipsson, 1788 (Bivalvia, Unionoidea, Unionidae) in The Netherlands

2012·11.7 MB·English

by  Nienhuis, Jozef A J H

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Two subspecies of Unio crassus Philipsson, 1788
(Bivalvia, Unionoidea, Unionidae) in The Netherlands
Jozef A. J. H. Nienhuis
VanGoghstraat24,NL-9718MPGroningen,TheNetherlands;
HayAmal18,Sefrou,Morocco
Introduction
TheformerdistributionofUniocrassusinTheNetherlands 107
isreconstructedonthebasisofthecollectionsoftheNether- OfthethreeUniospeciesthatwerelivinginTheNether-
landsCentreforBiodiversityNaturalis,Leiden,andthe landsuntilrecently,U.crassusPhilipsson,1788,istheone
privatecollectionoftheauthor.Themostrecentrecordof mostsensitivetopollution(Patzner&Müller,2001:328)and
liveU.crassusinTheNetherlandsdatesfrom1967,when mostclearlyrestrictedtostreamingfreshwater.Especially
twoindividualswerecollectedintheBiesbosch,inthe duringtheseventiesofthelastcenturytheRhineandMeuse
southwesternpartofTheNetherlands.Arathercommon becameheavilypolluted(Middelkoop,1998:67).Asaconse-
formofU.tumidusPhilipsson,1788,herereferredtoas quence,U.crassuswasnotobservedaliveanymoreafter
formacurtushasoftenbeenconfusedwithU.crassusand 1967intheNetherlands.Theexactperiodinwhichitbe-
hascausedconsiderablemisunderstandingaboutthe cameextinctwillneverbeknown.Intheearlyninetiesofthe
distributionofthatspeciesinthepast.Nexttothemost lastcentury,H.Wallbrink,Nieuwegein,andtheauthor
commonsubspecies,U.crassusriparius,U.c.crassusis begananintensivesearchforU.crassus,butfoundonly
reportedasasecondsubspeciesfromthenortheasternpart shellswithabrownperiostracum.Nowherespecimenswith
ofTheNetherlands.Theconchologicaldifferencesbetween aperiostracumwithyellowandgreencolourswerefound.
thetwosubspeciesaredescribedandillustrated.Anewway Becauseittakes10to20yearsafterdyingtodevelopshades
ofmeasuring,usingtheprodissoconchinsteadoftheumbo, ofbrown(Nienhuis,2003:81)wecanacceptthatUniocras-
isintroduced. susbecameextinctintheNetherlandsbefore1980.
In1990(personaldata)fourofthefiveUnionoidae
Keywords:Unionoidea,Uniocrassusriparius,Uniocrassuscrassus,Unio species,whichwereknownfromthetwolargeDutchriver
tumidus,morphometrics,taxonomy,TheNetherlands. systemsbeforetheseverepollutionstartedwerefoundalive
again,atleastatspecieslevel(insomecasesdifferentforms
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orevensubspeciesmayhavereinvadedTheNetherlands),
viz.Uniopictorum(L.,1758),U.tumidusPhilipsson,1788,An-
odontaanatina(L.,1758)andPseudanodontacomplanata(Ross-
mässler,1835).ItcanbeexpectedthatU.crassuswillonce
alsobefoundaliveagainifthewaterqualitycontinuesto
improve.
Muchincorrectinformationaboutthedistributionof
Uniocrassuswaspublishedinthepast.Mostofthemistakes
havetodowithaformofU.tumidus,whichisforconven-
iencecalledformacurtushere.Becausethecardinalteethof
U.crassusdifferfromthoseofU.tumidus,thetwospecies
canbedistinguisheddespitethesimilarityingeneralshape.
InthisarticletheconchologicaldifferencesbetweenU.cras-
susandU.tumidusformacurtusareclarifiedandtheirfor-
merdistributioninTheNetherlandsissummarized.
Moreover,U.crassusisdealtwithinmoredetailsinceit
turnedoutthatthisspecieshasbeenrepresentedbytwo
forms.Forthemomentbeing,wellawareofthedifficulties
intherecognitionofsubspeciesinU.crassusonthebasisof
shellcharactersonly(Nagel,2011),theseformsaregiven
thattaxonomicstatushere.
108
Material and methods
AllthespecimensofUniocrassusthatwerepresent2004in Fig.1.RecordsofUniocrassusripariusC.Pfeifer,1821,andU.c.crassus
theZoologicalMuseum,Amsterdam,andintheNational Philipsson,1788,intheNetherlands.18means1918etc.Onlythespotin
MuseumofNaturalHistory,Leiden(recentlyunitedasthe thenorth-eastoftheNetherlands(‘96’)referstothelattersubspecies.
NetherlandsCentreforBiodiversityNaturalis,Leiden)were Οcollectedaliveorwithfleshrests;□Periostracumyellowwithgreen
studied(seeFig.1),aswellasthesamplesintheprivatecol- orwithshadesofbrown(only‘39’and‘96’);?nodatesavailable(colln
lectionoftheauthor.Alltheshellshaveatleasttracesofthe C.H.Oostingh;MeppelerDiep,collnM.M.Schepman;
periostracum.Duringthisstudy,threecategoriesofspeci- OudeIJsselandKrommeRijn).
mensaredistinguished:(1)animalscollectedaliveorshells
withremainsofflesh,ayellowperiostracumwithgreenrays
(changingintobrowninalcoholmaterial),whichissome-
timescoveredbyadarklayer;(2)shellswithayellowand (nextpage)Fig.2.Uniotumidusformacurtus.a-d,Collectedaliveinthe
greenperiostracum,withoutanyremainsofthesoftparts; Vecht,DeHaandriknearGramsbergen,ProvinceofOverijssel,2004.
(3)shellswithalightbrownperiostracumwithdarkrays.In Exampleoflessabruptdiminishingdiameter.Shelllength5.3cm(leg.
allcategoriesbothvalvescanbefoundstilltogether.When J.A.J.H.Nienhuis).e-h,CollectedaliveintheOudeRijn,Herwennear
morethanonecategorywaspresentinasamplethebest Lobith,ProvinceofGelderland,1981.Exampleofabruptdiminishing
preservedspecimendeterminedthecategory(Fig.1).Cate- diameter.Shelllength7.6cm(leg.J.A.J.H.Nienhuis).
gory(3)isonlyindicatedinFigure1whenthereisnosam- PhotographsbyJ.Goud,Leiden.
pleofthecategories(1)or(2)knownfromnearby.
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Formeasurementswereused:9shellsfromtheDrentseAa
and52fromtheWaalnearDoodewaard,19extremelywell
preservedshellsfromtheMeuseintheprovincesofNoord-
BrabantandLimburg,6shellscollectednearLeiden,3shells
collectednearUitgeestandtheonlyknownshellfromthe
Dinkel.
Results
Historicaldata.‒InTheNetherlands,thelastsampleoflive
Uniocrassuswascollectedinthesouthwesternpartofthe
country,intheBiesbosch,on6.ii.1967(Wolff,1968:25).Two
animalswithshelllenghtsof6.0and6.7cm,respectively,
werecollectedintheSteurgat,HetKooike,atadepthof3-4
m.IntheMeusethelastproofofliveU.crassus(6.1cm)was
establishednearRoosterenin1946byW.H.Neuteboom.
Bothrecordsareofadultanimals.Becausejuvenileanimals
aremuchmoresensitivetoeutrophicationthanadultones
(Patzner&Müller,2001:328),itispossiblethatreproduction
hadceasedalreadylongbefore1967.Thatmightexplain
whyinasampleof320valvesofsubrecentU.crassus(Colln
Nienhuis),collectedin1996and2003intheWaalnearDoo-
110 dewaard,allshellsareover4.0cmlong.
OutsidetheDutchlargeriversystemspopulationsofU.
crassuswereknownfrom:(1)alocalitynearUitgeestnear
Alkmaar,provinceofNoord-Holland;(2)theVlietandthe Fig.3.RecordsofUniotumidusformacurtus.?nodatesavailable(colln
OudeRijn,nearLeiden,provinceofZuid-Holland;(3)the C.A.vanderWilligen;KrommeRijn);18means1918etc.except02and
Dinkel,nearDenekamp,provinceofOverijssel;(4)the 04whichmustbereadas2002and2004.SeeFig.1forexplanationof
DrentseAa,nearGlimmen,provincesofGroningenand othersymbols.
Drente.
U.crassuswasonlyfoundinsmalltolargestreamingwa-
ters.ThedatapublishedbyWolff(1968:27)aremainly tiesuptoonly0.5‰(Jaeckel,1960:207[althoughreferring
basedonU.tumidusformacurtus(seenextparagraph)or toU.c.crassus]).ThepopulationsfromnearUitgeestmight
deadU.crassusandcannotcontributetoabetterunder- haveoccurredinrunningwatersflowingfromthedunesa
standingoftheecologyofU.crassusinTheNetherlands. littlemoretothewest.
Theprovenanceoftwosamplesallegedlycollectedinthe
UitgeestermeernearUitgeestremainsunclear.Theywere Uniotumidusformacurtus.‒Sincetheshapesoftheshellsof
mostcertainlynotcollectedinthatlake(W.J.Kuijper,per- UniotumidusformacurtusandU.crassusoverlaptosomeex-
sonalcommunication,2004),sincein1937and1941,shortly tent,specimensofbothspecieshavebeenmisidentifiedreg-
aftertheclosingoftheAfsluitdijkin1933,thesalinitiesin ularlyinthepast.ThevarietyofU.tumiduswithshortshells,
theAlkmaardermeer,whichwasdirectlyconnectedwiththe referredtohereasformacurtus,hascausedmuchconfusion.
Uitgeestermeer,were1.51‰and0.67‰,respectively ItalwayslivestogetherwithnormalUniotumidus,towhich
(Anonymus,1946:68),whereasU.crassuscantoleratesalini- itisconnectedbyintermediateforms.[Kobelt(1880:32)de-
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Fig4.JuvenilespecimensofUniocrassusripariusandU.c.crassus.a-b,UniocrassusripariuscollectedaliveintheMeuse,Niers,provinceofNoord-Bra-
bant,A.M.H.Schepmanleg.,1912;shelllenght1.7.cm.c-d,UniocrassuscrassuscollectedwithoutfleshrestsintheDrentseAanearGlimmen,provinces
ofGroningenandDrenthe,H.J.Kwant,Haren,leg.2000;shelllength2.9cm.PhotographsbyJ.Goud,Leiden.
scribedUniotumidusvar.RohrmannifromSchwiersenear sharpandlong,andpointapproximatelytotheoutlineof
OelsinSilesiaforapopulationwithshortshellsthatare theshell,whereasinU.crassustheseteetharebluntand
moreflattenedhowever,thantheshellsfromTheNether- short,andpointtotheinsideoftheshell.
lands]. Uniotumidusanditsvarietieshavethesameformof
InU.tumidusbothcardinalteethintheleftvalveare rugaeontheumbo.AlmostalwaysU.tumidusformacurtus
Nienhuis,J.J..–TwosubspeciesofUniocrassusintheNetherlands
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Figs5-8.MeasurementsinUniocrassusripariusof5differentlocalitieswhicharelumpedtogether(blackrhombs)andU.c.crassusfromtheDrentse
(opensquares),withregressionlinesandcorrelationcoefficients.5,maximumdiameterversuslength;6,heightversuslength;7,anteriorpart(deter-
minedafterGittenbergeretal.,1998)versuslength;8,anteriorpart(determinedasdescribedinthispaper)versuslength.
Fig.9,FullygrownUniocrassus.a-c,U.c.ripariuscollectedaliveinthe
startsgrowinglikenormalU.tumidus,butafterhaving Meuse,Eegden,provinceofLimburg,byComitéOnderzoekMaasfauna
reachedalenghtof2.5-6.8cmthegrowthatthedistalend leg.,1918,shelllength7.0cm.Withremainsofadductormuscles;
maydecreaseratherabruptly,whichresultsinanirregular d-f,U.c.crassuscollectedwithoutfleshrestsintheDrentseAanear
diminishingofthediameterfromthatpointon.Amorenor- Glimmen,provincesofGroningenandDrenthe,H.J.Kwant,Haren,
malgrowthatthedistalendmayberesumed,however.Es- leg.2000;shelllength5.4cm.PhotographsbyJ.Goud,Leiden.
peciallywhenthereisamoregradualchangeingrowing,
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theshellsmaybecomeverysimilartoU.crassusinshape. DutchwaterswhereUniocrassusonceoccurred,wheresome
UniotumidusformacurtuscanstillbefoundaliveinThe gene-flowmighthavebeenpossible.Accordingtoforexam-
Netherlands,whereitisalwaysaccompaniedbymore‘typi- pleEhrmann(1933[1956]:224),Falkneretal.(2002:171),
cal’U.tumidus.Thespeciesoccursinstagnanttostreaming Haas(1969:45),Jaeckel(1952:19),Jungbluth(1973:162),
waters(Gittenbergeretal.,1998:179),butitsformacurtus Modell(1924:47;1941:169),andNesemann(1993:21),U.c.
wasneverobservedinstagnantwater.Maybethisvariety crassusisthesubspeciesthatisrepresentedintheScandina-
shouldbeconsideredagrowthdisorder,causedbyheavy vianglacialarea,sothatbiogeographicallyitmaybeconsid-
infestationofthemantletissueatthedistalendbywater- eredmostlikelythatU.c.crassusonceoccurredintheDutch
mitesofthegenusUnionicola,whichdifferintheirecological provinceofDrente.ThenearestrecordforU.c.crassusmen-
requirements.Maybeaspeciesofwatermitespreferring tionedintheliteratureistheWeser(Ehrmann,1965:224;
streamingwaterisinvolved,whatmightexplainwhyUnio Haas,1969:45;Nesemann,1993:21;Gloër&Meier-Brook,
tumidusformacurtusisrestrictedtothattypeofhabitat.See 2003:72).IlookedforU.crassusintheElbeinvain.
forgeneralinformationontherelationsbetweenmitesofthe Ehrmann(1956:224),Gloër&Meier-Brook(1994:69),
genusUnionicolaandUnionidaeinEuropeDavids(1973), Haas(1969:45,52),andJaeckel(1952:20,Fig.8)giveinfor-
Hevers(1975,1980)andMitchell(1953). mationconcerningthepresenceofadorsalcurveandthe
lesspronouncedumboinUnioc.crassusasopposedtoU.c.
UniocrassusripariusandU.crassuscrassusinTheNether- riparius.Theirdatadonotcontradicttheresultsobtainedfor
lands.‒In1996,bottomsamplesweredredgedfromthe thetwoformsofU.crassusthatonceoccurredinThe
DrentseAa,abrookinthenortheasternpartofTheNether- Netherlands(Fig.8).
lands,betweenHarenandTynaarloandshellsofU.crassus Zettler(1997:218)givesextensiveinformationconcerning
withabrownperiostracumwereselectedfromthemud.In length,height,widthandweightfor27populationsofUnio
114 2000additionalmaterialwascollectedbyH.J.Kwant, crassusinGermany(Mecklenburg-Vorpommern),Estoniaand
Haren.ThispopulationdiffersfromtheU.crassusfrom Lithuania.Becauseallthesepopulationsarefoundinthe
otherlocalitiesinTheNetherlands,whichhasbeenclassi- Scandinavianglacialarea,they‘should’belongtoU.c.
fiedwithU.crassusripariusC.Pfeiffer,1821(=U.c.batavus crassus.Thequantitativedatashowthatthevariouspopula-
sensuauct.,=U.c.nanusLamarck,1819[Gittenberger& tionsarequitevariableinmostrelativedimensions,sothat
Janssen,1998:176]:seeFalkneretal.,2002:172).Inshells Zettler(1997:225)concludesthatinnorthernEuropeU.c.
longerthan4cm,theanteriorpartisshorter,i.e.measures crassusisthemostvariableunionoid.Nevertheless,according
lessthanaquarterofthetotalshelllength,theumboispro- totheliteraturetheratioanteriorpart/shelllengthforU.c.
trudingless,andthereisa‘dorsalcurve’.Ifalineparallelto crassusisveryconstant,i.e.23-25%(Table1).Zettler(1997)
thelengthaxisandtouchingthedorsalsideoftheoutlineof doesmentionneitheramoreorlessprotrudingumbonorthe
theshelldoesnottouchtheumbo,thevalveissupposedto dorsalcurvethatisshownonhisillustrations,however.
havea‘dorsalcurve’.ThischaracterstateisveryrareinU. WhileinvestigatingthedifferencesbetweentheDutch
crassusriparius(seeFig.9).Moreover,therugaeofajuvenile populationsofUniocrassusripariusandU.c.crassus,three
shellthatwasfoundintheDrentseAadifferfromthoseofa ratioswerestudied,viz.height/length,maximumdiame-
specimenofU.c.riparius(seeFig.4),butsincethesetwo ter/lengthandanteriorpart/length.Measuringthevarious
specimensaretheonlyonesavailableandbecauserugae dimensionsismorecomplicatedthansuggestedbyGitten-
provetobeveryvariableevenwithinpopulationsofUnio berger&Janssenetal.(1998:17)onthebasisofapictureof
speciesingeneral(personalobservation),thismightnotat Uniopictorum.Forthatreason,themeasurementsarede-
allbediagnostic. finedhereinmoredetail.
TheDrentseAamaybeconsideredisolatedsinceit Usually,asinGittenberger&Janssenetal.(1998:17)the
drainsintotheDutchWaddenSea,incontrasttotheother anteriorpartoftheshellisdeterminedasthedistance
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betweentheprojectionoftheumboonthelengthaxisand icallyreadingandcommentingonthemanuscript;H.K.
theanteriorside.Becauseumbonescanberatherflatorcor- Kaput,Assen,fortypingandcorrectingtheoriginalmanu-
rodedhowever,theexactspotfromwhichtomeasurecan script;W.J.Kuiper,Noordwijk,forinformingmeonbrackish
poseproblems.Onthecontrary,thelocationoftheprodisso- watermolluscsandUnionoidae;H.J.Kwant,Haren,for
conch,i.e.theformerglochidium,canbedeterminedexactly. showingmeadditionalU.c.crassusoftheDrentseAa;R.G.
Here,theanteriorpartisdefinedasthedistancebetweenthe Moolenbeek,Amsterdam,fortheloanofU.crassusofthe
projectionoftheprodissoconchonthelengthaxisandthe ZoologicalMuseum,Amsterdam;F.P.Wesselingh,Leiden
anteriorside(seeFigs7,8).Theshellheightismeasuredper- fortheloanoffossilU.crassusoftheNCBNaturalis;A.J.de
pendicularlytothelengthaxis,asthedistancebetweenthe Winter,Wageningen,formakingthegraphs.
umboandthelineparalleltothelengthaxistouchingthe
ventralside.Bydiameterthediameterofacompletespeci- References
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