An interesting achatinid (Gastropoda, Pulmonata, Achatinidae) and other land snails from Benguera Island off central Mozambique

2007·0.87 MB·English

by  Van Bruggen, A C

BASTERIA,71:105-110,2007
Aninteresting achatinid(Gastropoda, Pulmonata, Achatinidae)
andotherlandsnailsfromBenguera Island
off central Mozambique
A.C. vanBruggen
National Museum ofNatural HistoryNaturalis,P.O. Box 9517,NL 2300RALeiden,The Netherlands;
[email protected]
Amedium-sized achatinid fromBenguer[u]aIs.inthepost-PleistoceneBazarutoArchipelago
offcentralMozambiqueisidentified asCochlitoma churchilliana (M.&P., 1895)sensulato,there-
by considerablyextendingtherange ofthis species(complex?) northward.Variation inapex,
size, shapeandcolour oftheshell ofthiscomplexisdiscussedindetail. Alsoincluded arefirst
recordsforthis island ofvarioussmall speciesoflandsnails fromleaf litter.Ofthese four,i.e.
Nesopupa farquhari Pilsbry, 1917 (Vertiginidae), Trachycystis rivularis (Krauss, 1848)
(Charopidae), Cecilioides pergracilis Connolly, 1939(Ferussaciidae), and CurvellaamicitiaeVan
Bruggen,1968(Subulinidae),arenewrecords forthe Mozambiquelist.
Key words: Gastropoda,Caenogastropoda,operculateland snails, Pulmonata,Achatinidae,
Cochlitoma, synonymy, variation, distribution, Vertiginidae, Charopidae, Ferussaciidae,
Subulinidae,faunistics,BazarutoArchipelago,Mozambique.
Omniadubia
The firstAfricanexploits of thewell-knownLeidenmalacologist Dr E. Gittenberger
havebeenacomplete success inso farthathemanaged tocollectsomevaluableandinter-
esting materialinboth Mozambique and Botswana (videVan Bruggen, 2006). Twicehe
and hiswifevisitedthe BazarutoArchipelago (2005,2006) situated NEof Vilanculos,on
the central Mozambique coast, where they collected land mollusc material on Ilha
Benguer[u]a (formerly Ilha deSantoAntonio) atMarlinLodge (on the western shoreof
theisland) inleaflitterundershrubsinthesanddunearea(fig. 1).Downs& Wirminghaus
(1997: 593)have summarily described the vegetation of Benguera Is.; it appearsthatthe
Gittenberger materialwas obtainedin evergreenduneforest/secondary dune forest.
Allmaterialhasbeen deposited in theNationalMuseumof NaturalHistory, Leiden
(abbreviated RMNH). Other abbreviationsused are 1/d for theratio length/maximum
major diameter of the shell as an indication of its shape, and 1/lw for the ratio
length/length lastwhorloftheshell.
Apart fromsmall shells of leaf litterdwelling species, their material also included
shellsof abeautifulachatinid.Initially thismaterialdefiedproperidentification;unfortu-
nately, notwithstanding athorough search in2006,nolive-collectedmaterialisavailable.
Thereis atotaloften medium-sized,fairlyslendershells, allwithaflamepattern(figs 2-
4,table1).Acarefulscrutiny of theliterature(also including Verdcourt,2006) and mate-
rialhasfinallyledtotheconclusionthattheshellsrepresentoneofthenorthernmostpop-
ulationsof Cochlitomachurchilliana.Fullsynonymyof thistaxon is shownbelow.
106 BASTERIA,Vol. 71, No.4-6,2007
Cochlitoma churchilliana(Melvill& Ponsonby, 1895)sensulato
Achatina churchilliana Melvill&Ponsonby, 1895: 164,pi. 12fig.3;Connolly, 1939: 308,pi. 11fig. 5.
Archachatina churchilliana - Sirgel, 2000:218, figs 10-13; 2002: 139, fig. 1; 2004:271,figs 1-3;Herbert &
Kilburn,2004:145, 6unnumbered figs.
Cochlitoma churchilliana - Mead, 2004:421.
Achatina zuluensisConnolly, 1939:308,pi. 10fig.2.
[Achatina(Lissachatina)craveninonSmith,1880- Van Bruggen,1969:35,fig. 11,should be Archachatina
zuluensis,rectified in VanBruggen&Appleton,1977:27]
Archachatina zuluensis - Van Bruggen&Appleton,1977: 25, figs5-7;Sirgel, 2000:216,fig. 9;2002: 139;
2004: 271.
Cochlitoma zuluensis- Mead,2004:423, figs 13,20-22.
Archachatina sanctaeluciaeVanBruggen,1989:169,figs4-5;Sirgel, 2000:216,figs7-9;2002:139,fig. 1;2004:
271.
Cochlitoma sanctaeluciae -Mead,2004: 422.
Locality data ofthenewmaterial:
-Mozambique,BazarutoArchipelago(NE. ofVilanculos),IlhaBenguer[u]a(formerly Ilha deSanto
Antonio),atMarlinLodgeinlitter undershrubs, 18.VII.2005,leg./don.E.Gittenberger(RMNH:3shells).
-Mozambique,ibidem,STAEG0612,26.VII.2006,leg./don.E.Gittenberger(RMNH: 7shells).
Threeseminalpapersby Sirgel (2000,2002,2004) havegreatly contributedto clarify
the status of the achatinids described s.n. Achatina churchilliana, A. zuluensis and
Archachatinasanctaeluciae.His findings maybesummarizedasfollows.(1) The shellsofall
threetaxa doshowconsiderableoverlap inapex,size, shape and colourpattern,infactall
are intergrading. (2) Thegenitaliaofallthreeformsaresimilar.(3) Breedingexperiments
haveshownthatthesetaxa in secondandthirdgenerations sometimesexhibitshellsthat
canbeidentifiedas belonging toother(conchological) taxa thantheparentgeneration. In
my view Sirgel has convincingly shown that the above three names are synonyms.
However, moleculardataare stilllacking. Also, thereare indications(e.g. in Herbert &
Kilburn, 2004: 146) thatthe threeformsarenotalways syntopic; they maybesubject to
differentpredatorpressureinthevarioushabitatsresulting incolourmorphsbeing select-
edagainst. Mead(2004)inhislistonpp.421-423appearsto entertainsomedoubtastothe
validityofthethreetaxa,atleasthedoesnot(yet?)considerthemsynonymous.Theabove
is thereasonwhy thesetaxa areshownheres.n.Cochlitomachurchillianasensu lato.
Generally there is a wide range in measurements in C. churchilliana, i.e.59.0-83.6 *
27.4-39.9 mm, 1/d1.66-2.46,1/lw1.33-1.65,whorls7-8Vz.Inhis 2002and 2004 papersSirgel
hasshownthatincaptivitythesanctaeluciaeformmay growtoa greatsize encompassing
morethan9 whorls in theprocess considerably increasing its 1/d, whilethe1/lwmoreor
less stays thesame:
Early stage 68.5 *30.2mm,1/d 2.27,length lastwhorl40.5mm, 1/lw1.69
Adultshell 93.5x 36.0mm,1/d 3.47,length lastwhorl56.0mm, 1/lw1.66
Inachatinidsitis difficulttoestablishwhichshellsareadultbecausethereis nothick-
ening of the outer lip. Table 1 shows the metric dataof the four largest Benguera speci-
mens andincludesthoseof amuch smallershell(2006c, fig.4) thatcouldbe takentobe
adult.Thesemeasurements areallwithintheknownrangeforwhatis consideredtobeC.
churchillianas.l.Thesmallestshell(i.e. 2006c)is anoddone;becauseof thefact thatithas
7 Vz whorls it might be considered adult, in which case it is outside the range of C.
VanBruggen:An interestingachatinidfromBenguera Island, Mozambique 107
Fig. 1.Habitat ofthe here discussedland snailsofBengueraIs.,BazarutoArchipelago,Mozambique— all
materialwascollected inevergreen dune forest/secondarydune forest.Photo E.Gittenberger,VII.2006.
Figs 2-4. Shells ofCochlitoma churchilliana s.l.from BengueraIs., Bazaruto Archipelago, Mozambique
(approximatelynatural size).2,specimenno.2006a(seetable1);3,no.2005b;4,no.2006c.PhotosJ.Goud.
108 BASTERIA,Vol. 71, No. 4-6, 2007
churchillianas.l. andmight evenqualify as a separatetaxon. Indeed, had this specimen
beenfoundas asingle shellandsubmittedforidentificationas such, it mighthavebeen
consideredarepresentative of apossibly undescribedtaxon characterizedby asmallish
and slendershellwithacomparatively high numberof whorls.However, inview of the
intraspecificvariation ofthetaxon herediscussed, itis takentobe anaberrantspecimen.
Specimen Shell length* 1/d Lengthlast 1/lw Aperture Ratio length Number
max.maj.diam. whorl lengthx shell/height ofwhorls
width aperture
2006a 75.0 x 32.3 2.32 49.1 1.51 31.9x20.3 2.35 8+
2005a 74.1 x29.5 2.51 48.0 1.54 31.4x 17.6 2.36 7%
2005b 60.0x27.0 2.22 43.0 1.39 29.6 x 17.1 2.03 7Vt
2006c 52.3 x 21.6 2.42 33.1 1.58 22.4 x 13.6 2.33 7%
Table1.Metric data ofthe fourlargestshells andasmallerspecimenofCochlitoma churchilliana s.l.from
BengueraIs.
Thenorthernlimitsoftherangeof C. churchillianas.l.arehithertounknown. Herbert
& Kilburn (2004: 145)state "InhabitstheZululandcoast,from theMtunziniarea north-
wardsinto southernMozambique (Maputo area), inlandtoNdumoGameReserve." The
distancebetweenMaputo and theBazaruto Is. ina straight lineis just under600 km, an
enormousextensionoftherangeofthistaxon.Inthesouthitdoesnot seemtooccursouth
of theThukela(formerly Tugela) River inKwaZulu-Natal.Thisalsoimpliesthat thecom-
plex does occur in suitablehabitatin coastal Mozambique between Maputo and the
BazarutoIs.Inaddition,itis likelytooccur furthernorthaswell.Sofarsimilarshellshave
notbeenrecordedfromcoastalTanzania(see e.g.Verdcourt,2006).
Alast question hereis the ageof theBazarutoArchipelago. Downs &Wirminghaus
(1997: 591)state"Thecoastalplain ofsoutheastern Africais characterizedbyanumberof
sand-dunebands, eachrepresenting aformershorelineof youngerage eastwardsasthe
sealevel fell(Hobday 1976).Present-day coastaldunesare estimatedto haveformedas
recentlyas5000yearsago(Fairbanks, 1989)whenthesearosetoitspresentlevel.Offshore
islandssuchas thoseoftheBazaruto Archipelagowere isolatedfromthemainlandbythe
rising sea-level atthis timeand representfragments ofprevious peninsulas. The islands
of the Bazaruto Archipelago were attachedto the mainlandfrom 90,000to 10,000years
ago(Ramsay, pers.comm). Thesealevelattaineditspresentlevel6500yearsago(Ramsay,
pers.comm)." Thisis confirmedby amore recent paperby Cooper & Pilkey (2002: 164),
who write in their abstract "Two barrier island systems from southern Mozambique
(Inhacaand Bazaruto)aredescribed.Bothsystems comprise acompositebarrierislandor
barrier island chain that developed ona steep continentalmargin as a result of initial
(Pleistocene)spit progradation."Thisimplies thatthe above discussedpopulationsof C.
churchillianaonBenguera Is. havebeen isolatedfromthose onthe mainland for atleast
10,000years or,in otherwords, are post-Pleistocene. Here is greatscopefora molecular
approach. Indeed, itis vitalto collect livematerialhere, study the genital anatomyand
perform aproperDNA analysis.
Atthesametimesomeothermaterialand leaflittersamples were takenmoreor less
atthespotwheretheachatinidshellswere found.Thefollowing species areputonrecord
here.
StaEG.0612(seeabove,7species): Nesopupafarquhari Pilsbry, 1917(RMNH104361/62,
VanBruggen: AninterestingachatinidfromBenguera Island, Mozambique 109
Vertiginidae), Gastrocopta damarica (Ancey, 1888) (RMNH 104358, Chondrinidae),
Afroguppya rumrutiensis (Preston, 1911)(RMNH 104355,Euconulidae), Cecilioidespergra-
cilis Connolly, 1939(RMNH 104360,Ferussaciidae), CurvellaamicitiaeVanBruggen, 1968
(RMNH 104359, Subulinidae), Achatina immaculata Lamarck, 1822 (RMNH 104357,
Achatinidae), Cochlitomachurchilliana(seeabove).
StaEG.0613,0.5km SEof MarlinLodge in litterundershrubsand trees,27.VII.2006,
leg./don. E. Gittenberger (allRMNH, noachatinids found; 10 species): Tropidophora cal-
carea (Sowerby, 1847) (RMNH 14363, Pomatiidae), Truncatella marginata Krister, 1855
(RMNH 14367, Truncatellidae), Melampus parvulus Pfeiffer, 1856 (RMNH 14368,
Ellobiidae), Nesopupa farquhari Pilsbry, 1917 (RMNH 104373,Vertiginidae), Gastrocopta
damarica(Ancey, 1888)(RMNH 104364,Chondrinidae), Trachycystis rivularis(Krauss, 1848)
(RMNH 104375,Charopidae), Afroguppya rumrutiensis (Preston, 1911)(RMNH 104369,
Euconulidae), Cecilioides pergracilis Connolly, 1939 (RMNH 104372, Ferussaciidae),
Curvella amicitiaeVan Bruggen, 1968 (RMNH 104371, Subulinidae), Gulellaperissodonta
(Sturany, 1898)(RMNH 104370,Streptaxidae; videVanBruggen, 2006:123). Thepresence
of twosemi-marine species, Truncatellamarginata and Melampus parvulus, in thematerial
ofthelaststation is anindicationthatthisis not farfromthe land-seaboundary.
Sofartheonly known published recordoflandmolluscsoftheBazarutoArchipelago
is thatof Gulellaperissodonta inVanBruggen (2006).Thereforeallabovespecies arenewto
this island group.Fourtaxa, i.e., Nesopupa farquhari, Trachycystis rivularis, Cecilioidesper-
gracilis, andCurvella amicitiaearenew totheMozambique list.
According to Herbert & Kilburn (2004: 114) Nesopupa farquhari occurs from the
Eastern Cape Provincein SouthAfrica to theMozambique borderin KwaZulu-Natal-
thereforethis is a considerablerange extension forthistaxon. Thisnamemaybe asyn-
onymofN. bisulcata(Jickeli, 1873),aspecies widely distributedinEastandCentralAfrica.
Herbert&Kilburn(2004:236) statethatTrachycystis rivularis(and probablesynonyms
T.ordinariaMelvill& Ponsonby, 1908,and T.persimilis Connolly, 1932), is widely distrib-
uted in SouthAfrica in (inland) KwaZulu-Natal, Gauteng, Mpumalanga and Limpopo
Province"onbushy hills".Sofarthiscomplex hasnotbeenrecordedfromZimbabweand
Mozambique. Theredonot seemto be coastalrecords, letalonefromdunevegetation at
sealevel-thisindeedmakestheBazarutoshellunusual.
Cecilioidespergracilis isarepresentative ofasubterraneangroupofwhichtheshellsare
difficultto identify. Presumably adult shells (whorls c. 5-5+) of the Bazaruto material
measure 3.0-4.7x 0.9-1.4mm, 1/d 3.33-3.57.Compared to metricdatain e.g. VanBruggen
& VanGoethem(2001:155-156,figs 2-12)andVanBruggen & Rolan(2003:97, fig.21)these
are very slendershellsandindeedarebest classifiedwith C.pergracilis. The distribution
ofthistaxon (seeVanBruggen &Rolan,2003,and Herbert& Kilburn, 2004) covers much
ofsouth-centralAfrica, reaching as farasnorthernKenya (Verdcourt, 2006).TheBenguera
record neatly fitsintothispattern.
Curvellaamicitiaeis a widely distributedtaxon(Herbert &Kilburn,2004: 138) known
fromKwaZulu-Natal(e.g.,coastallocalities), theKrugerNationalPark, andZimbabwe,so
thattheMozambique records arenot unexpected.
Dr Dai Herbert, in reviewing the manuscript, notedmaterialin theNatal Museum
(Pietermaritzburg, SouthAfrica), possibly belonging to C. churchilliana(and also other
smallspecies discussedabove),fromPomeneBay (= PontadaBarra Falsa) at22°55-56'S,
35°35'E,andalsoXaiXai at"25.11324°S:33.74019°E".Thiswouldfillthegapbetweenthe
BazarutoArchipelagoand Maputo Province in Mozambique.
Acknowledgements are due toDr E.Gittenberger forentrusting thematerialto the
110 BASTERIA,Vol. 71,No. 4-6,2007
presentauthor,toDr D.Herbert(NatalMuseum) forcontributing vitalliteraturedataand
commentingonthemanuscript, andtoMrJ.Goud(RMNH) forthesplendid photographs
of theshells.
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