The terrestrial Mollusca of Easter Island (Gastropoda, Pulmonata)

9 Pages·2001·1.9 MB·English

by  Boyko, Christopher B

BASTERIA, 65:17-25, 2001
TheterrestrialMolluscaofEasterIsland(Gastropoda, Pulmonata)
Christopher+B. Boyko &James+ R. Cordeiro
Division ofInvertebrate Zoology,AmericanMuseumofNatural History, Central ParkWestat79th
Street,New York,NewYork, 10024
[email protected]
The terrestrial Mollusca ofEaster Islandaresurveyed,based onpublishedrecords, museum
material, and recent collections in 1999. Six species areknown withcertaintyfrom Easter
Island,five ofwhichhave nearlyworldwide distributions.All areknown orsuspectedtobe
human introductions.Allopeasgracile(Hutton)isreportedforthe firsttimefromEaster Island
and thepreviousrecord ofDeroceraslaeve(Müller)issuggestedtobemisidentified D.reticula-
tum(Müller).
Keywords: Gastropoda,Pulmonata,biogeography,introduced species,Pacific,Easter Island.
INTRODUCTION
ThesmallsouthPacificlandmassof EasterIsland, orRapa Nui,is situatednearly 3800
km fromthe SouthAmericanmainland(Chile) and over2200km from PitcairnIsland,
it's nearestneighbour tothe west. Theislandisofvolcanicoriginandcontainsno conti-
nentalor sedimentary rocks (Fischer & Love, 1993),only aggregations of shellandcoral
sandonandneartheislandsfewbeaches.Theterrestrialinvertebratefaunaissparseand
only the insects have beenstudied in any detail(Campos &Pena, 1973). There are few
records ofterrestrialmolluscs on EasterIslandin the literatureand nosynthesis ofthe
data.Thisis in marked contrast to ourknowledge ofthe marinemolluscs, which was
summarizedby Rehder's (1980) monograph and added to by otherrecent papers (e.g.
Osorio, 1991;1995). Thepresentstudy, basedonallknownliteraturerecords aswellas a
collectionby oneoftheauthors(CBB) in 1999,summarizes theinformationavailableon
the terrestrialmolluscsofEaster Island.This reportis confinedto thosetaxa whichare
trulyterrestrialanddoesnot includemarinepulmonate taxa(e.g.,Siphonaria, Melampus;
seeRehder [1980] foradetaileddiscussion ofthese taxa).
The first record ofany terrestrialmollusc from Easter Island was a “Parmarionsp."
(Ariophantidae) by Fuentes (1914). Noariophantid slugs have subsequently beenrepor-
ted from Easter Island and, in the absence ofvoucher material, this record remains
unconfirmed.Wesuspect thatFuentes'(1914)Parmarionwas actually oneoftheintrodu-
cedslugspecies subsequently reported. Dall (1908) reported the nowcosmopolitan (ori-
ginally circum-mediterranean) slugMilaxgagates(Draparnaud, 1801) from underrocks
nearthe shore.Odhner (1922) reported this species as well, and addedtwo more taxa:
Limaxarborum Bouchard-Chantereaux, 1838,andhis new genus and species Pacificella
variabilisOdhner, 1922.Although not implicitly statedby Odhner, P.variabiliswas des-
cribedas the first endemicterrestrialmolluscfromEasterIsland. However, itwas later
shown toalso occur on many ofthe Pacificislands to the west (see Cooke & Kondo,
BASTERIA, Vol. 65,No. 1-3,2001
18
1961). Theonly other reports ofterrestrialmolluscs from Easter Island were those of
Rees(1955), who alludedtothepresence ofHelixaspersaMidler, 1774,andSteele(1957),
whomerely compiled alist ofprevious records. Walden(1962) correctedthe identifica-
tionofthe EasterIslandLimaxspecies toLimax(Lehmannia) valentiana(Ferussac, 1821),
basedondissectionofthe specimens reported byOdhner (1922), butdidnot reportany
newmaterial.
Kuschel (1963) discussed the relationships of the terrestrial Easter Island faunawith
selectotherPacificislandsandcitedfivespecies ofmolluscs. Heonly cited onetaxon by
name(Melampuspascus Odhner, 1922),but the Milax, Limax andPacificella, as well as a
,
secondspecies of Melampus[later shownby Rehder(1980) tobea misidentifiedM. pas-
cus] mustlogically have comprised hislist. Klemmer& Zizka (1993) repeated Kuschel's
(1963)fivetaxa,including the"two"Melampusspecies, andlistedPacificella variabilis as an
EasterIslandendemic. Themostrecent informationavailableonEasterIslandterrestri-
almolluscswasin ashortpaperbyNaranjo-Garcla &Appleton (1999), wherethey added
HelixaspersaandDeroceraslaeve(Miiller, 1774) to thefaunallist.
In 1999,oneofus (CBB) spentthreeweeks onEasterIsland aspart ofa surveyofthe
marine invertebratefauna; there was also opportunity to collect terrestrial fauna on
numerous occasions, especially when the weather was too poor for marine work.
Localitieswere sampled throughout the island, withthe exception of the Mt.Terevaka
areawhich was not visited. True to the nature of an islandwith depauperate biota, the
samples yielded very few specimens ofterrestrial molluscs, with only a single species
(Helix aspersa) being foundin substantialnumbers.Allofthe terrestrialmolluscswere
found nearareas ofhumanhabitation, current or past, andnone were foundin more
remote areas ofthe island such as the Poike peninsula. Additionally, only a very few
examplesofeachspecies werefounddespite intensivesearches ateachlocation.Limited
asthese samples were, they containedtwo cosmopolitan taxa previously unreported, or
reportedbutmisidentified,fromEasterIsland,andprobably introducedafter 1917when
the last major collectionsofterrestrialmolluscs were made (see Odhner, 1922). These
samples, combinedwith Odhner's (1922) specimens, allowed thiscomprehensive sum-
maryofthe terrestrialmollusctaxa. Themostimportant conclusionthatcanbe drawn
is that Easter Islandappearsto have noendemic terrestrialmolluscanfauna,which is
perhaps not surprisinggiven itslocationandextreme isolation.
Unless otherwisenoted, allliteraturecitationsreferto recordsofspecimens collected
from Easter Island. The specimens collected in 1999are deposited in the American
MuseumofNatural History, NewYork (AMNH); all of Odhner's specimens are in the
collectionsoftheSwedishMuseumofNaturalHistory (SMNH). In'Materialexamined'
thenumberofspecimens isaddedafterthecollectionno.
SYSTEMATICACCOUNT
FamilyAchatinellidae
Pacificella variabilisOdhner, 1922
Pacificella variabilis Odhner,1922: 249-252,pi. 8, figs 15-17;Steele, 1957: 113 (list);Klemmer &Zizka,
1993:24.
Tornatellinops variabilis (Odhner); Cooke & Kondo, 1961: 172-175, figs 76a-h,77; Naranjo-Garcia &
Appleton, 1999: 120, 121.
Boyko &Cordeiro: TerrestrialMolluscaofEasterIsland
19
Material examined. —Sta.707,EasterIsland (RapaNui),2.vii.l917,coll. K.Backstrom(SMNH 1668/5
shells,syntypes).
Distribution. — This species is widely distributed on Pacific islands, from Truk
(Carolines) to Easter Island (Preece, 1995: 287), and north to the Mariana Islands
(Bauman, 1996: 19). Themapgiven by Cooke& Kondo(1961: fig.77) includedatleast
67 islandsfromwhichthe species was known atthattime. Many ofthose islands have
distinctive morphotypes (Preece, 1995:287) thatmayrepresent endemic subspecies or
even species, so the true range of this taxon (as definedby the type specimens from
Easter Island) is unclear. Although originally described from Easter Island (Odhner,
1922),the species mostlikely was transported thereby humans froman unknownsour-
ce population elsewhereinthe Pacific.
Remarks. —Although the habitatof thisspecies onEasterIsland hasnotbeen repor-
ted, itisabundantonbothnativeandintroducedplants onPitcairnIsland(Preece, 1995:
287). Itwaserroneously calledanEasterIslandendemicby Klemmer& Zizka(1993: 24).
Itsplacement inPacificella Odhner, 1922,ratherthanTornatellinops Pilsbry, 1915,was con-
firmedbybothPreece (1995) andCowieetal. (1995). Nospecimens were foundin 1999.
Odhner's (1922) specimens in SMNH are syntypes, as are the "paratypes" in the
Bishop Museum, Hawaii,citedby Cooke&Kondo (1961: 172).
Family Limacidae
Lehmanniavalentiana(Férussac, 1821)
Limax arborum Bouchard-Chantereaux;Odhner, 1922: 249;Steele, 1957: 113 (list). Not L. arborum
Bouchard-Chantereaux,1838,asynonym ofL. marginatusMiiller,1774.
Limax (Lehmannia)valentiana (Ferussac);Walden, 1962:71-92,figs 5-7.
LimaxmarginatusMidler;Naranjo-Garcia&Appleton,1999: 120,121. NotL. marginatusMiiller,1774.
Material examined. — Sta. 705, Easter Island (Rapa Nui), 2.vii.l917, cod. K. Backstrom (SMNH
28094/7).
Distribution.—This nearly cosmopolitan ground-dwelling (non-arboreal) slug is nati-
vetothe IberianPeninsula,but hasbeenwidely spread byhumans(Kerney, 1999: 160).
Walden(1962: 88-90) cited this species as occurring on allcontinents except Asiaand
Antarctica. InNorthAmerica, it islargely confinedto greenhouses (Chichester & Getz,
1973:36).
Remarks.—Thisspecies hasbeenreported fromEasterIslandunderthenameL. arbo-
rumor itsseniorsynonymL. marginatus(see Pilsbry, 1948:529). Walden(1962) dissected
oneoftheaboveexaminedspecimens, recognized thismisidentification, andnoted that
many recordsofL. marginatus from tropical andsubtropical countrieswere actually L.
valentiana.Nospecimens were foundonEaster Islandin1999.
Deroceras reticulatum(Müller, 1774) (fig. 1)
?Deroceras laeve (Midler);Naranjo-Garcia&Appleton,1999:121. ?NotD. laeve(Midler,1774).
20 BASTERIA, Vol. 65,No. 1-3,2001
Fig. 1. Deroceras reticulatum(Müller, 1774) from AnaTe Pahu, Easter Island (RapaNui), largest specimen,
2.3 cmlength(AMNH300602).
Material examined. —Under leaflitter indepressionofcollapsedlava tubenearcavemouth,AnaTe
Pahu,Easter Island (RapaNui),21.viii.1999,coll.C. B.Boyko (AMNH300602/2).
Distribution.—Thisspecies isnativeto Europe andis foundin mostofNorthAmerica
andmany temperateand subtropical countries. It hasbeen introducedand spread by
commerce throughout every temperateand subtropical region with European settle-
ment(Burch, 1962:83; Robinson, 1999:table 1).
Remarks. — This species was the eighth most common mollusc intercepted by the
United States Division of Plant ProtectionandQuarantine in import shipments from
1993-1998(Robinson, 1999:table 3). It isoften found confinedto towns,farmlands,or
gardens andlives in open places, pastures, arable fields, roadsides,landfills, and urban
gardens (Chichester & Getz, 1973;Kerney, 1999);itwasfoundonEasterIslandin anarea
showing clearsigns ofpast humanhabitationand some cultivation.Muchoftheleaflit-
terwas banana(Musaspec.), whichonly growsin such humidandwind-shelteredareas
onEasterIsland(Flenley, 1993: 13).
An undeterminedspecies ofDeroceras, close to, orperhaps identicalwith, D. reticula-
tum,was foundonPitcairnIslandin 1991and was also suggested to beofrecent intro-
duction(Preece, 1995:302).
Both this taxon and D. laeve have been reported from Hawaii as introducedtaxa
(Cowie, 1997:22). Typically, ofthesetwo slugs, D.reticulatumistheone foundin invasive
situations (Robinson, 1999: table 1), but the reverse appears to be true in Hawaii.
However, Cowie(1997: 22) notedthatthe two species names mayhavebeen usedinter-
Boyko &Cordeiro: TerrestrialMolluscaofEasterIsland 21
changeably whenreferring to Hawaiianspecimens, making identificationsinthe litera-
ture questionable. Thepresent specimens from Easter Island are clearly D.reticulatum
because they possess awhite-borderedbreathing pore onthe mantle more anteriorly
locatedthan thatofD.laeve. Dissectionofone specimen from EasterIsland confirmed
thisidentification,basedonthemorphology ofthemale genitalia, especially the charac-
teristic shape andthickness ofthe distal portion ofthe penis (see Kerney &Cameron,
1979). Because the commonly introducedDeroceras foundworldwideis D. reticulatum,
andbecauseourspecimens arealso thisspecies, westronglysuspect thatthesolerecord
of D. laevefrom Easter Island (Naranjo-Garcia & Appleton, 1999: 120) was based ona
misidentification.Attempts toborrow thematerialofNaranjo-Garcia &Appleton (1999)
from the Universidad Nacional Autonoma de Mexico for direct examination were
unsuccessful, dueto the inaccessibility ofthe collectionwhich was being moved at the
timeofourrequest. However, Naranjo-Garcia (pers. commun. 11April2001) informed
us thatthe specimens they dissected (number unspecified) "fully agreewith the shape
drawn of the female(aphallic) form in page 147 of Kerney & Cameron [1979, for D.
laeve].” Intheabsenceofacomparison ofadultmale penis morphology, weare hesitant
to agreewiththeir conclusions as totheidentity ofthose specimens. Only furthercol-
lecting, anddissectionof moremale genitalia, willanswerthe question ofwhetherthere
are two species ofDeroceraspresentonEasterIsland.
Family Milacidae
Milaxgagates(Draparnaud, 1801)
LimaxgagatesDraparnaud;Dall,1908:435.
Milaxgagates(Draparnaud); Odhner, 1922: 249;Steele,1957: 113 (list); Naranjo-Garcia&Appleton,
1999:120, 121.
Material examined. — Sta. 705, Easter Island (Rapa Nui), 2.vii.l917, coll. K. Backstrom (SMNH
28091/3).
Distribution. — This is a cosmopolitan species now, native to Europe and the
Mediterraneanbasinthathasbeenintroducedintonumerous countriesonallcontinents
exceptAntarctica(Robinson, 1999:table 1).Robinson(1999: table1)listedthisspecies as
absentfrom easternAsiaandthe oceanicislands ofthe Pacific,butithasbeenfoundin
shipmentsofplants fromChinaand Singapore (Dundee, 1974: 16) andoccurs onEaster
Island(Dall, 1908;herein).
Remarks. —LikeallterrestrialmolluscsonEasterIsland,except Helixaspersa, thisspe-
ciesis apparently notvery common as no specimens were foundin1999.
Family Subulinidae
Allopeas gracile(Hutton, 1834) (fig. 2)
Material examined.—Under leaflitter indepressionofacollapsedlavatubenearacavemouth,Ana
Te Pahu,Easter Island(RapaNui),21.viii.1999,coll. C.B.Boyko(AMNH300603/9).
Distribution.— This species is probably the most widely ranging of all land snails
(Pilsbry, 1946: 177-178). Of presumed tropical American origin, it has been introduced
intogreenhouses inthesoutheasternUnited States(Burch, 1962: 127),Mexico (Branson
22 BASTERIA, Vol. 65,No. 1-3, 2001
Fig. 2.Allopeasgracile(Hutton,1834)fromAnaTe Pahu,Easter Island (RapaNui), largest specimen, 1.0cm
shelllength(AMNH300603).
& McCoy, 1965: 10),andthroughout thetropics ofbothhemispheres (Pilsbry, 1946: 177
178;Robinson, 1999:table1). Itis hereinrecordedfrom EasterIsland forthe firsttime.
Remarks.—AllopeasgracilewasfoundonEasterIsland inassociationwithpast human
habitationandcultivation, inthe samehabitatasDerocerasreticulatum.Although onlycol-
lectedas shellmaterialin 1999,itlikely persists onEasterIsland asthe habitatis favou-
rableforthespecies.
This species was recorded as a probable recent introduction to Pitcairn Island by
Preece (1995: 295).
Family Helicidae
Helix aspersa Müller, 1774(fig. 3)
Helixaspersa Miiller;Rees, 1955:93; Naranjo-Garcia& Appleton,1999: 121
Material examined. — On various ornamental plants, vicinity ofHotelTopara'a, HangaRoa,Easter
Island(RapaNui),20.viii.1999,coll. C.B.Boyko(AMNH300601/5).
Boyko &Cordeiro: TerrestrialMolluscaofEasterIsland 23
Fig. 3.Helixaspersa (Müller,1774).A,photographedinsitu ongroundsofthe Hotel Topara’a,Easter Island
(RapaNui); B,specimenscollected from same site; largest specimen,3.1 cmshelllength(AMNH300601).
Distribution.—Nowacosmopolitan species, native toEurope andthe Mediterranean
basin, it has been introduced into numerous countries on all continents except
Antarctica, including many Pacificislands (Robinson, 1999:table 1).
Remarks. —The occurrenceof this species onEaster Island is not surprising, given
that it is perhaps the most widely and most often distributedintroduced pulmonate.
Indeed, H. aspersa was the most common mollusc intercepted by the United States
Division of Plant Protectionand Quarantine in imports during 1993-1998(Robinson,
1999:table 3). Itis typically foundin gardens, grasslands, woods and dunes(Kerney,
1999:205). On Easter Island, it was found only in the vicinity ofthe solesettlementof
Hanga Roa. Although only afewspecimens were collected, itwas observed tobe very
abundanton ornamental plants around houses. As with introductionsofthis species
elsewhere, itmayhavebeen deliberatelybrought to EasterIslandforuseasfood.
Rees (1955: 93) was thefirstauthorto citeH.aspersaas occurringonEasterIsland,but
gave noreference for thisinformationand wehave beenunableto track the source of
hisrecord. Itispossible thatpart ofRees's (1955: 93) statementaboutdistributionwasa
generalized remarkonsnailbiogeography, rather thanalist oflocalitiesfromwhichH.
aspersawas known. Support forthis hypothesis comes from thefact thatalthough Rees
(1955) listed Pitcairn Islandamong those islands reached by "the common snail," H.
aspersa is nototherwiserecordedfromthatisland (Preece, 1995). Likewise, Rees(1955)
mentionedHawaiiin the questionable paragraph, butH.aspersa was not well documen-
ted from there until a year later (Kondo, 1956: 141); its brief earlier mention in a
Hawaiianentomologicaljournal [Anonymus, 1953]no doubtescaped the noticeofmala-
cologists. Naranjo-Garcia & Appleton (1999: 121) provided the only other recordofthis
species from EasterIsland.ThepresentrecordofH.aspersais thereforeonly the second
well-documentedonefrom EasterIsland.
24 BASTERIA, Vol. 65,No. 1-3,2001
ACKNOWLEDGEMENTS
Funding toCBB for the InvertebrateSurvey ofEaster Islandwas provided by the U.
S. National Park Service (USNPS), Gateway National Recreation Area, Division of
NaturalResources,as partofaScienceMuseumofLong Island/Explorers Clubfive-year
research expedition to explore the impacts ofEl Ninoevents onWorldHeritage Sites.
John Tanacredi(USNPS) is thankedfor making this Survey possible. PaulaMikkelsen
(AMNH) and an anonymous individualkindlyreviewed the manuscript andsuggested
valuableimprovements. All photographs bySteve Thurston(AMNH) excepting fig. 3B,
whichis by CBB.
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