Gulella (Juventigulella) ngerezae spec. nov. (Gastropoda, Pulmonata, Streptaxidae), a new endemic land snail from the Ukaguru Mountains, Tanzania

2007·1.3 MB·

by  Rowson, B

BASTERIA, 71: 221-227,2007
Gulella(Juventigulella) ngerezae spec.nov.(Gastropoda, Pulmonata, Streptaxidae),
anew endemiclandsnail fromtheUkaguru Mountains,Tanzania
B. Rowson
Dept.Biodiversity&SystematicBiology,National MuseumofWales,CardiffCF10 3NP,UK;
[email protected]
A new species ofland-snail (Streptaxidae: Gulella) from montane forest in the Ukaguru
Mountains (Tanzania) is described and attributed to subgenusJuventigulella Tattersfield on
shell characters.Thereareshell and radular resemblances tocertainotherGulella speciesnotin
subgenusJuventigulella,emphasisingthe needforrevisionary work.This isthe second endem-
ic snail described fromthe Ukagurus,arecognisedareaofendemismbut onefromwhichfew
land snailshavebeencollected.
Key words:Gastropoda,Pulmonata,Streptaxidae,Gulella,taxonomy,endemism,montanefor-
est, EasternArcMountains,Tanzania, EastAfrica
INTRODUCTION
Tattersfield(1998)describedthreenewspecies ofGulellaL.Pfeiffer, 1865,fromforests
inTanzaniaandgrouped themintoanew subgenus, Juventigulella Tattersfield,basedon
shared features of shell size, shape and apertural dentition.He concludedthat there
remained"much tobe learned about the smallerelements in the Tanzanian andEast
Africanterrestrial molluscfaunas". Thepresent paperaffirms this by describing anew
species which,although assigned to Juventigulella, shares certainfeatureswithTanzanian
species assigned toother(or no)subgenera ofGulella,emphasising theneedfortaxonomic
work in thisunderstudiedgroup.
The new species was collected in 2004 from asingle site inMamiwaKisara North
ForestReserve,ononeofthehighestridgesoftheUkaguru Mountains,MorogoroRegion,
Tanzania.The reserve, an importantwater catchment fortheGairoarea, is characterised
by forestsof the'EasternArc'typeonacidiclithosolsoverlyingPrecambriangneiss, with
ameanannualrainfallofaround1400mm(Lovett&Pocs, 1993).Amongmanyothermol-
luscs, atotaloffivespecimens of thenewspecies were foundbydirectsearching (20 per-
son-hours) of leaflitterand rotting woodin anarea (approx. 200 ofbroken-canopy
montane forestat1700melevation, about0.5km insidethenorthernreserve boundary.
Landmolluscsalready reported frommontane forestintheUkaguru massifinclude
theendemicPseudopeas ukaguruense Verdcourt, 1996(Subulinidae) (Verdcourt, 1996)and
two unnamed, undescribed streptaxids listed by Verdcourt (2006). These are ("Gulella
(Primigulella) sp. cf. usagarica [Crosse, 1885]") from "Mnyera Ridge" and ("Gulella
(Aenigmigulella) sp.") from"MamiwaRidge"(Verdcourt, 2006).Bothofthesecanbetraced
backtoVerdcourt(1978)wheretheywere listedas“Gulella(Primigulella) sp." and “Gulella
sp. nov." respectively. Although eachwas represented only by a single juvenile shell,
Verdcourt'sdescriptions are sufficienttobe sure thatneitherofthestreptaxids is conspe-
cificwiththe newspecies describedhere. Both thesetaxa, andP. ukaguruense, were the
product of incidentalcollecting by thebotanist D. J. Mabberley in 1972(Verdcourt, 1978,
1996), after which it seems no substantialmollusc collectionshave been madein the
Ukaguru montane forests. With the Ukaguru Mountainsforming part of the famous
222 BASTERIA,Vol. 71, No. 4-6, 2007
EasternArc, a region characterised by highrates ofendemismacross many taxonomic
groups(see Burgess et al., 2007, for a recent review) itis likely that further land snails
endemictoUkaguru remaintobe discovered.
In thefollowing description, collectionsareabbreviatedas follows: NMW,National
MuseumofWales,Cardiff, UK(NMW accessionsinzoology havea"Z"following theini-
tials); NMT, NationalMuseumsof Tanzania,Dar es Salaam,Tanzania.
DESCRIPTION
Gulella(Juventigulella) ngerezaespec. nov. (figs 1-8)
Material examined. - Tanzania, Morogoro Region,Kilosa District, MamiwaKisara North Forest
Reserve(approx.6 25'S,3657'E),at1700m,foundbydirectsearchingofwetleaflitterandrottingwood,
30.vi.2004,leg.C.F. Ngereza,P.Tattersfield,and B.Rowson. This isthe typelocality.Holotype:onelive-
collected adult,alittle worn(NMW.Z.2004.016.00002).Paratypes 1-5(dataasabove):four live-collected
juveniles (NMW.Z.2004.016.00003-5 and NMT), and one dead-collected juvenile (NMW.Z.2004.
016.00006).Specimens preserved in80% ethanol,except forparatype4(NMW.Z.2004.016.00005)pre-
served in96% ethanolat-35 C,andparatype2(shelldried and coatedforSEMexamination).
Diagnosis. - Aspecies of Gulella(sensu lato) with asmall, characteristically-shaped
shellwithopenumbilicus, spiral apicalsculpture, andsemi-regular radiallamellae.Inthe
adulttheperistome iscomplete andhas av-shaped parietaltooth, aweakbasalswelling,
andaweakcolumellarswelling. Younger juveniles haveaweak parietalkeel.
Description of holotype - Shellof the only knownadult specimen (figs. 1-3)small
(h2.25 mm x wl.95 mm), of 5.75 whorls, subcortical, with apex wide and slightly
mucronate, and body whorl narrower than, and slightly displaced below preceding
whorl.Umbilicusopen,perspective andslightly eccentric.Surfaceofprotoconch (firsttwo
whorls) as viewedunderalight microscope (*60magnification) finely, irregularly granu-
lar withfainttraces of spiral threads, apparently worn away in many places. Surfaceof
subsequent whorls characteristically interrupted at semi-regular intervals by slightly
curved radial lamellae, thesetypically running fromsuture to suture andincreasing in
size and curvature onlaterwhorls. In contrast, lamellaeof apertural sideof body whorl
less prominent andnot extending toumbilicus.Shell surfacebetween lamellaeof faint,
irregular radialstriae, becoming strongonly onlastthirdof body whorl. Last quarterof
body whorl slightly constricted by aweak,broad spiral depression on columellarside.
Peristome subcircular, complete, reflected and well-demarcated from attachment to
penultimate whorl by a deep suture. Apertural dentitionconsisting of (1) a strong, v-
shaped parietal tooth,projecting a littleoutofaperture (thus creating a smallnotch or
sinusin palatal partof peristome) andcontinuing intoaperture as a shortlamella; (2) a
weakbasalswelling ortooth,setjustbehind theperistome;(3) aweakcolumellarswelling
ortooth, setjustbehindtheperistome. Inaddition,a secondbulge (butnot thickeningof
theshell) occurs onthecolumella, setjustbehind(2)and(3), corresponding tothedepres-
siononthecolumellarsideofthebody whorl.
Additionaldescription from paratypes (all juveniles). - Surface of protoconch (first
two whorls) much less worn, very finely granular with numerous fine spiral threads,
Rozvson: Gulellangerezaespec.Nov.from the Ukaguru Mountains, Tanzania 223
Figs 1-8.Holotype and paratypes ofGulella (Juventigulella)ngerezae spec. nov., NMW.1-3, holotype;4-5,
apicalsculpture ofparatype2;6-7, radula ofholotype, 8,bottom view ofparatype 5showingparietal
keel.
224 BASTERIA, Vol. 71,No.4-6,2007
about 13onthesecondwhorl(figs 4& 5). Umbilicusopenandperspective at all growth
stages. Apertural dentitionofjuveniles limitedto a veryweak mid-parietalkeel entering
theaperture inyoungspecimens (paratype 5; fig. 8);thiskeel notpresentintheaperture
of morefully-grown specimens (otherparatypes), soevidently notcontinuous withadult
parietal tooth.
Dimensions. - See table1.
Table 1.Details ofthe sixknown specimens.Shell heightand widthmeasurementsinmm.Width meas-
urementsinclude lamellae. *Shell ofparatype5brokenbackalittleto expose parietalkeel(fig.5).
Status Accession number State Height Width Whorls
Holotype NMW.Z.2004.016.00002 Liveadult 2.25 1.95 5.75
Paratype 1 NMT Livejuv. 1.45 1.80 4.5
Paratype2 NMW.Z.2004.016.00003 Live juv. 1.55 1.80 5
Paratype 3 NMW.Z.2004.016.00004 Livejuv. 1.55 1.75 4.75
Paratype4 NMW.Z.2004.016.00005 Livejuv. 1.50 1.80 4.75
Paratype 5 NMW.Z.2004.016.00006 Deadjuv. 1.45 1.70 4.5*
Anatomy. - Radulaewereextracted fromtheholotype and fromparatype 2. Radula
long, narrow, ofv-shaped rows (fig.6). Centraltooth elongate, about thesamelength of
theninthlateraltooth,withacentralcuspthatinterlocks withthebaseofthecentral tooth
of the following row (fig. 7). Lateral teeth monocuspid, elongate, tall but strongly
recurved,with anelongate areaofbasal attachment,lacking abasalanchor sensu Aiken
(1981). Onehalf-row comprises 7-9lateral teeth,the second,thirdandfourthteethbeing
thelargest, withtheeighth and ninthbeing thesmallest. Icouldnot determinethenum-
berof rows owing to thevery smallsize of the radula,butit is atleast30 andprobably
notmorethan60.Otheranatomyunknown.
Distribution.- Known onlyfromthetype locality. Numerous surveys in otherparts
of East Africahavenot foundthis species (e.g. those listed in Seddonetal., 2005;NMW,
unpublished).
Etymology. - This species is dedicated to my Tanzaniancolleague Mrs Christine
Fishaa Ngereza of NMT, for her invaluable help with all aspects of NMW's work in
Tanzaniasince 1997.
DISCUSSION
I considerG.(J.) ngerezae unmistakableamongtheEastAfricanfauna(see diagnosis).
However,there areresemblancesto thefollowing fivesmall, East Africanspecies, which
havebeencompared directlywiththeholotype:
1. Gulella(Juventigulella) amboniensis Tattersfield, 1998.- G. (J.) ngerezaeresemblesthis
species insize, thestrongradial lamellae,and intheparietalkeelofyoungjuveniles. Itdif-
fers in adult apertural dentitionand inhaving spiral embryonic sculpture. It is amoot
point whethertheoverallshellshapeofthetwo species is consideredsimilarordifferent,
G.(J.)amboniensisbeing conicalratherthansubcortical,butalsobeing theleaststrictly con-
Rowson: Gulellangerezaespec.Nov. from the Ukaguru Mountains, Tanzania 225
ical (i.e., highest-spired) of the three species originally assigned to Juventigulella by
Tattersfield (1998). I consider G. (J.) ngerezae intermediatein shape between G. (J.)
amboniensisandG. peakei continentalis(seebelow). G.(J.) atnboniensisisknown from mon-
tane forestintheEast Usambara MountainsinNE. Tanzaniaandthe nearby coastalfor-
est(Tattersfield, 1998).
2. G. (J.) habibuiTattersfield, 1998. - G. (J.) ngerezaeresemblesthis species in sizeand
intheparietal keelofyoungjuveniles. Itdiffersinbeing relatively higher-spired, inhav-
ing strongerradiallamellae,in adultapertural dentition,andinhaving spiralembryonic
sculpture. G.(J.) habibuiisknown frommontane and lowlandforestfromvarioussites in
NE. Tanzania(Tattersfield, 1998).
3. G.(J.)spinosa Tattersfield, 1998.- G. (J.) ngerezaeresemblesthis species insizeand
shape (juvenilesofG. (J.)spinosa mayyetprovetohaveaparietalkeel), butdiffersinmany
otherrespects. G.(J.) spinosa isknown frommontane forestonKilimanjaro, Tanzania,and
in theTaitaHills, Kenya (Tattersfield, 1998;Lange etal., 2001).
4.G. kimbozaeVerdcourt,2004.- G.(J.) ngerezaeresemblesthisspecies in thecomplete
peristome andstrong radiallamellae, and in having a spiralelementto the embryonic
sculpture (that of G. kimbozae is described as "spirally punctate striate" by Verdcourt,
2004) butdiffersinmanyotherrespects. G.kimbozaeisknown only fromlowlandforestat
Kimboza, in thefoothillsoftheUluguru Mountains,Tanzania.
5. G. peakei continentalis van Bruggen, 1975.- G. (J.) ngerezaeresembles thisspecies in
the complete peristome and strongradiallamellae.Young juveniles of G.p. continentalis
also havea parietalkeel (vanBruggen, 1975),although there aredifferencesin theaper-
tural dentition, sizeand shape; G. p. continentalisalso lacks spiral embryonic sculpture.
The radulaof G. peakei (presumably subsp. continentalis) fromeastern SouthAfricawas
describedand figured by Aiken (1981), who notedthatit was unique among the South
African Gulellaradulaehestudiedin severalrespects. TheradulaofG. (J.) ngerezaeresem-
blesthatofG. p. continentalisinthegeneralform,number,andrelativesize ofthelaterals,
but differs considerably inthe formof the central tooth, which was said tobe "minute
[and] amorphous" byAiken(1981). Thecentral toothof G.(J.) ngerezaeis relatively large
andcharacteristically-shaped in comparison. Thesecomments apply tothesubspecies G.
peakeicontinentalisbutone canassumethattherelationship withtheextinctAldabransub-
species G.p. peakei van Bruggen, 1975, is similar. G. p. continentalisisknown frommany
localitiesfromeastern SouthAfricatoTanzania,Kenya andUganda (Rowson,in press).
All the above namedspecies except iG. p. continentalis are restricted to forest in
Tanzania orthe EasternArc Mountains.Based oncurrent data,G.(J.) ngerezaeis themost
restrictedof thesespecies withtheexception ofG. kimbozae, andmayprovetobeendem-
ic only to theUkaguru Mountains.Itis worthnoting thatG. (J.) ngerezaeshares morpho-
logicalfeatureswithspeciesofJuventigulella aswellaswithspecies notcurrently assigned
to that subgenus, and that in overall shell form it appearstransitionalbetween G. (J.)
amboniensisand iG.peakei, withwhichit alsoshowsaradularresemblance.Inevitably, my
attributionofthenewspecies toJuventigulella thusexpands themorphologicalcontent of
the subgenus. Theapparently complex patterns of similaritiesand differencesbetween
thesespecies warrantfurtheranalysis, aspotential synapomorphies ofJuventigulella or an
asyetun-circumscribedlargergroupofspecies currentlyassigned to Gulellasensulato.
Specialmention maybe madeofthespiral striaeontheembryonic whorls, afeature
thatnoneoftheaboveEastAfricanspecies shareswithG.(J.) ngerezae.Featuresofthepro-
toconch arise early in ontogeny, so might be considered phylogenetically important
according to vonBaer's 'first lav/ (to paraphrase: general, i.e. primitive, features of a
226 BASTERIA,Vol. 71, No. 4-6, 2007
groupappearearlierinontogenythanspecial, i.e. derived,features). Ifthiswere thecase,
they should be given greater weighting in systematic studies. Asurvey of the known
African Streptaxidae suggests this weighting has not been consistently applied, and
indeedthatembryonic sculpture has notbeenconsideredofparticular importance inthe
group.Pilsbry's (1919) monograph ontheterrestrialmolluscsoftheCongo basin,andthe
subsequent revisionof his groupsby laterauthors, will serve as an example. Although
Pilsbry(1919)usedembryonic sculptureasasubgeneric or genericcharacterinotherfam-
ilies, the situationis differentin hislarge streptaxid subfamily Ptychotrematinae. Pilsbry
circumscribesthe Ptychotrematine subgenus EnneaH. & A.Adams, 1855, onteleoconch
characters, and groupstogether species having embryonic spiral striaewithspecies hav-
ing smooth embryonic whorls. The type species of the then monotypic subgenera
AvakubiaPilsbry, 1919,and Conogulella Pilsbry, 1919,haveembryonic spiral striae, but so
does at leastone species that Pilsbry (1919) assigns to Gulella sensu lato (no subgenus
named) onteleoconchcharacters. Embryonic spiral striaewere evidently not considered
sufficientto defineasubgenus. Pilsbry's (1919) subgenus Tortigulella Pilsbrywas founded
ontwootherwisedissimilarspecies withdecussateembryonic sculpture including aspi-
ral element, but has since been expanded by Verdcourt (2006) to include East African
species with differentembryonic sculpture. The subgenus Parennea Pilsbry, 1919, was
foundedonspecies with smooth embryonic sculpture (or thosefor which no datawas
given),buthas sincebeenexpanded by Adam& VanGoethem(1978)to include several
species withdecussate embryonic sculpture. If, as is very likely, eachof theseclassifica-
tionsare intendedto reflectphylogeny, thecurrent arrangementimplies repeated evolu-
tionary loss or gainofthevarious formsof embryonic sculpture. Protoconchfeaturesare
thus homoplasious and likely to be of limited phylogenetic valueamong African strep-
taxids, whileteleoconch charactershavebeen given greater weight in past revisions. It
willbe intriguing toexamine thesystematic valueofjuvenile teeth- an ontogenetically
early teleoconch feature - now that more data on them is becoming available.
Furthermore, thesuperficially juvenile appearanceofcertain species ofJuventigulella, and
other streptaxid taxa, raises the question of whether ontogenetic shifts havebeenmore
important in streptaxid evolutionthan changes in the protoconch. Such shifts could
explain the shell form of G. (J.) ngerezae being intermediatebetween that of G. (J.)
amboniensisand G.peakei; onewonderswhatmight explain theevolutionineither direc-
tion.
ACKNOWLEDGEMENTS
IamindebtedtoPeterTattersfield(NMW)andChristineNgereza (NMT),withwhom
the materialwas collected, NMW for funding the fieldwork, the Tanzanian authorities
who granted research permits and access, andto thepeople of the Mandege area near
MamiwaKisara whoassistedwiththesurvey. Mary SeddonandPeterTattersfield(NMW)
provided comments onthemanuscriptandAnnaHolmes helpedwithSEMfacilities.
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