Diversity and Decline of Land Snails on Rota, Mariana Islands

15 Pages·1996·6.5 MB·English

by  S Bauman

Diversity and decline of land snails on Rota, Mariana Islands
Scott Bauman
University ofGuam, MarineLaboratory, Mangilao,Guam 96923
Abstract: Thisstudyreviewsthelandsnail faunaofRotatoassessthediversityofthefauna(basedonrecentfieldcollectionsandtheliterature)andthe
status ofeach speciesencountered(currentlyextant vs. apparently extinctbut known from historically collected live specimens vs. known only from dead
material). This informationcanbe usedtodeterminetheconservationneedsoflandsnailsonRotaandto provide insights intothe origin andevolutionary
historyofthefauna. Two known landsnail predatorshave beenintroducedontoRotasinceWorld WarII: the predatory flatwormPlatydemusmanokwari
DeBeauchamp, 1962, and thepredatorygastropodGonaxiskibweziensis (Smith, 1894). Ofthe43 speciesencounteredon Rota,9% areconsidered surviv-
ing well, 23% have questionable survival status, 56% are in decline, and 12% are potentially extirpated. Mariana Island land snails are more widespread
among the islands ofthe archipelago than Hawaiian land snails. Single island endemics constitute 87% ofthe Oahu fauna but at most 31% ofthe Rota
fauna. The more widespread distribution of Mariana Island land snails could be related to the frequent typhoons that track across the island group. It
appearsthatspeciationwithintheMarianaIslandshasoccurredatleastinthefamiliesAssimineidae,Charopidae,andPartulidae.
Terrestrial gastropods are possibly the most extinc- anthropogenic activity (Balouet and Olson, 1989). The only
tion prone organisms on oceanic islands (Hadfield et ai, way to do this is to sample past faunas through the fossil
1993; Paulay, 1994). Many insular land snails have restrict- record. On islands the best preserved fossil faunas typical-
ed ranges and small population sizes, making them espe- ly are of land snails and vertebrates. Erroneous biogeo-
cially sensitive to introduced competitors, predators, and graphical and evolutionary theories can be drawn from data
habitat destruction (Hadfield et ah, 1993). Also, certain collected only from recent faunal and floral surveys
species have been over-collected by shell enthusiasts in the (Steadman, 1993).
past (Hadfield, 1986; Solem, 1990). Because many species In the Mariana Islands, the Partulidae have been
ofland snails on oceanic islands evolved in situ, underlim- extensively studied (Crampton, 1925; Kondo, 1970; Hopper
ited predation pressures, they tend also to possess few and Smith, 1992; Smith, 1993) while other land snails have
adaptations protecting them from introduced predators received little attention aside from taxonomic studies
(Cowie, 1992). (Quadras and Moellendorf, 1894a, b; Baker, 1938; Abbott,
Two known land snail predators have been intro- 1949; Cooke and Kondo, 1961; Solem, 1983; Kurozumi,
duced on Rota since World War II: the predatory flatworm 1994). While Guam was extensively surveyed for land
Platydemus manokwari De Beauchamp, 1962, and the snails in the late nineteenth century by J. F. Quadras
predatory gastropod Gonaxis kibweziensis (see Eldredge (Quadras and Moellendorff, 1894a, b), the other islands in
and Smith, 1994). The predatory gastropod Euglandina the archipelago were little studied before the 1920s.
rosea (Ferussac, 1818) has been introduced onto Guam, Crampton and Kondo made notable land snail collections
however, E. rosea was not found on Rota during 1994, on Rota in 1925, 1949, and 1952. While numerous species
1995, or 1996. Neither is there any indication in the litera- have been described and recorded from Guam, few records
ture of the occurrence of this species on the island. These have been published from otherislands in the archipelago.
three predators, especially P. manokwari and E. rosea, have The objectives ofthis study were to review the land
been implicated in declines of land snails on several snail fauna ofRota, specifically to determine (1) the diver-
Mariana Islands, as well as on other islands around the sity of the fauna, based on recent field collections and the
Pacific (Hadfield and Mountain, 1980; Clarke et ai, 1984; literature, and (2) the current status ofeach species (extant,
Murray etai, 1988; Hopperand Smith, 1992). apparently extinct but known from historically collected
To fully understand the evolution and biogeography live specimens, or known only from dead material). On the
of insular faunas, it is important to examine the diversity basis ofthese data I will evaluate the conservation status of
and distribution of the organisms prior to the onset of the fauna, as well as its origin andevolutionary history.
AmericanMalacologicalBulletin,Vol. 12(1/2)(1996):13-27
13
14 AMER. MALAC. BULL. 12(1/2) (1996)
MATERIALS AND METHODS mulated on the forest floor. Searching less accessible
microhabitats, such as under bark and deep in rock cracks,
Rota is the second southernmost island in the was limited at some sites because oftime constraints.
Mariana Islands, just north of Guam (Fig. 1). During July Voucher specimens ofall specieshave been deposit-
1994, March 1995, and April 1996, I searched for and col- ed in the University of Guam Invertebrate Collection, and
lected subfossil and living land snails at 26 sites on Rota where available in sufficient numbers, in the Bernice R
(Fig. 2). Land snails other than partulids were collected at Bishop Museum (BPBM). Catalog numbers cited are from
14 ofthe 26 sites surveyed. The July 1994 collections were the Bishop Museum's Malacological Collection catalogs.
from paleontological excavations at Payapai Cave and As The status of each species (Table 1) was coded as
Matmos Cliffside Cave (sites 20 and 12 respectively). follows. A species was considered "declined" ifit was col-
These sites along with a preliminary list of vertebrate lected at < 5 sites as dead shells only or ifcollected at > 5
remains from them, were described by Steadman (1992 and sites with < 20% ofthe sites having live animals. A species
unpubl.). Land snails at these sites were picked from sedi- was considered "possibly extirpated" on Rota if it was col-
ments sieved through ca. 1.6-mm mesh screens. The March lected at > 5 sites with no living animals found. A species
1995 survey focused on living land snails and associated was considered to be surviving well on Rota if it was col-
land snail death assemblages (i.e. subfossils). This was part lected at > 5 sites, with > 50% of the sites having living
of a joint University of Guam and U. S. Fish and Wildlife populations. Species collected at < 5 sites with some sites
Service survey ofpartulid tree snails on Rota; I was invited supporting living populations and those collected at > 5
to survey other terrestrial snails. During April 1996, two sites with 20-50% ofthe sites supporting living populations
days were spent searching for snails at two sites already were considered as surviving with uncertain status.
studied during March 1995. At each site I searched micro- I have used three designations to refer to species
habitats for live snails and also collected dead shells accu- which are not definitely identified. Species names preced-
ed by "cf." are represented by specimens that are close to
the nominal form, but differ slightly from it. Species names
preceded by "aff." are represented by specimens that differ
sufficiently from the nominal taxon to be considered specif-
Uracas
ically distinct. Species names preceded by a "?" refer to
Maug specimens that were either too poorly preserved for defini-
• Asuncion tive identification, or whose identity with the respective
nominal taxon could notbe fully ascertained.
o Agrihan
p Pagan
RESULTS
• Alamagan
• Guguan
Tables 1 and 2 summarize the status and collection
information for each species on Rota. Additional details
• Sarigan
are treated in the systematic sectionbelow.
Anatahan
• Farallon
deMedinilla
MARIANA SYSTEMATIC REVIEW
0 Saipan
ISLANDS 0 Tinian
" Aguijan Class GASTROPODA
Subclass PROSOBRANCHIA
o Rota Family HYDROCENIDAE
Solem (1988), Thompson and Dance (1983), and
Guam Thompson and Huck (1985) provided useful recent reviews
ofPacific Hydrocenidae. Three species ofhydrocenidshave
been described from the Mariana Islands; two of these are
Fig. 1. Map of the Mariana Islands. Inset depicts the location of the here recorded from Rota. These are the first published
MarianaArchipelagointhewesternPacificregion. records ofGeorissa from Rota.
BAUMAN: LAND SNAILS OF ROTA 15
Fig.2.MapofRotaindicatingthelocationsofsitessurveyed.
Genus Georissa Blanford, 1864 Family TRUNCATELLIDAE
Georissa elegans Quadras and Moellendorff, 1894 Fig. 6
Fig. 3 Truncatellids tend to occur in marginal marine habi-
Shells of Georissa elegans have a sculpted and tats. This habitat type was not thoroughly searched on Rota
angled body whorl compared to the more rounded and in 1995. One colony ofan unidentified truncatellid was dis-
weakly sculptured shell ofG. laevigata. G. elegans was not covered on Rota in 1988 at Pona Point (B. Smith, pers.
found alive on Rota. G. elegans was described from Guam comm.). Live snails were still present at this site in 1995.
and figured by Zilch (1973a). No other truncatellids were found alive although numerous
fragments were discovered at three othersites. PonaPoint is
Georissa laevigata Quadras and Moellendorff, 1894 a limestone plateau raised ca. 7-10 m above sea level, and is
Fig. 4 covered with short grasses growing on limestone, which has
Georissa laevigata was described from Guam and very little soil or sand and is in the spray zone of large
figured by Zilch (1973a). G. laevigata is widespread and waves. The assimineids Omphalotropis suturalis, and
abundant on Rota. It was found among limestone rubble Omphalotropis sp. 7 are microsympatric with this truncatel-
andon the undersidesofrotting leaves. lid species on Rota. The same truncatellid species and O.
suturalis inhabit and co-occur in similar habitats on
Family DIPLOMMATINIDAE Guam.
Genus Palaina Semper, 865
1
Palaina taeniolata Quadrasand Moellendorff, 1894 Family ASSIMINEIDAE
Fig. 5 The Assimineidae is the most diverse family ofland
This species was described from Guam; Zilch snails in the Mariana Islands, with 25 species recorded from
(1953) figured the lectotype. Live animals are abundant and Guam (Smith, 1993). Lectotypes and holotypes of 22
widespread on Rota. Animals are common on the under- species described by Quadras and Moellendorff (1894a, b)
sidesofrotting leaves andon limestone rubble in forests. were illustrated by Zilch (1967). While only six species
3467
AMER. MALAC. BULL. 12(1/2) (1996)
Table 1.RangeamongthesouthernMarianaIslandsandstatusofspeciesfoundonRota. Islandoccurrences(numbers
refer to references) 1, Baker, 1938; 2, Cooke and Kondo, 1961; 3, Zilch, 1973a; 4, Zilch, 1953; 5, Zilch, 1973b; 6,
Solem, 1983; 7, Kondo, 1970; 8, Abbott, 1949; 9, Smith, unpubl.; 10, Solem, 1988; 11,Tsuda, 1969; 12, Muniappan,
1983; 13,Lange, 1950; +,newrecord;cf.,newrecordofcf.nominalspecies.Range: I,introduced; M,MarianaIslands;
R, Rota endemic; W, wide ranging; +, new record; ?, range not known at this time. Status on Rota: D, declined; E,
potentiallyextirpated; S,surviving;S?,survivingwithquestionablestatus.
IslandOccurences
Species Guam Rota Tinian Saipan Range StatusonRota
Georissaelegans 3 + 13 M D
M
G.laevigata 3 + S
M
Palainataeniolata 4 + 13 S?
Truncatellidaesp(p). s + 13 ? S?
?Allepithemasp. 1 + R S?
Omphalotropiscookei X + X M D
O.elongatula 9 + M E
O.laevigata 9 + 1 M D
O.octhogyra 9 + M D
O.semicostulata 9 + M D
O.submaritima 9 (cf.) 13 M D
O.suturalis 9 + M S''
0.quadrasi X + M D
O. sp. 1 + R D
0.sp.2 + R D
O.sp. + R D
O. sp. + R D
O. sp.5 + R D
O. sp. + + M D
O. sp. + R S?
Paludinellaconica X + 8 M s
Quadrasiellaclathrata 9 + M D
?Q. sp. 1 + WR D
Pythiascarabaeus 9 + 13 E
Pacifwella ?variabilis + + W,I? S?
Lamellideasubcylindrica 2 2 M D
M
L.microstoma 2 2 2 2
M
Elasmiasquadrasi 2 2 2 2 S
Gastrocoptasp(p). 10 + 13 I,? E
Nesopupasp(p). 9 + 13 I,? D
Partulagibba 7 7 7 7 M D
P.cfVaff.gibba + R S?
Samoanafragilis 7 7 M S?
Gonaxiskibweziensis 11 I D
Subulinaoctona 9 + 13 I S?
Succineasp(p). 9 + 13 ? E
Achatinafulica 12 12 12 12 I E
Himeroconchasp. 1 + R D
H. sp.2 + R D
Semperdonheptaptychius 6 + M D
M
S.rotanus 6 6
S. sp. 1 + WR D
Liardetiatenuisculpta 1 1 W
L.doliolum 1 1 1
L. sp(p). + ? S
M
Lamprocystisfastigata 1 1 1
L.sp(p). + 13 ? S?
?Genus?species + [,? D
1
BAUMAN: LAND SNAILS OF ROTA 17
were collected alive on Rota, an additional 13 were encoun- although 14 other land snail species were found as subfos-
tered as subfossils. sils in leaf litter and soil samples. Traces of the predatory
flatworm, Platydemus manokwari, were noted at this
GenusAllepithema Tomlin, 1931
site.
?AUepithema sp. 1
Fig. 7
Omphalotropissemicostulata Quadras and
This species is tentatively placed in Allepithema. It Moellendorff, 1894
is distinct from the six species of Allepithema described Fig. 12
from Guam by Quadras and Moellendorff (1894b), and is This species was previously known only from
only known from Rota. A single living animal was found at Guam. No living animals were found.
each oftwo sites.
Genus Omphalotropis Pfeiffer, 1851 Omphalotropis cf. submaritima Quadras and
This is the most diverse genus of land snails on Moellendorff, 1894
Rota and Guam. Smith (1993) listed 16 species from Fig. 13
Guam; 15 species are here recorded from Rota. Omphalotropis cf. submaritima can be distin-
guished from the similar O. suturalis by its larger size and
Omphalotropis cookei Abbott, 1949 more rounded sutural ramps. Dead shells ofO. cf. submar-
Fig. 8 itima were found at one site on Rota. Previously this
Omphalotropis cookei is distinguishable from other species was only known from Guam and Saipan.
Rota Omphalotropis by the presence of"pronounced spiral
threads" (Abbott, 1949). Abbott (1949: 265) stated, "0. Omphalotropissuturalis Quadras and Moellendorff, 1894
cookei is closest in morphological characters to Omphalo- Fig. 14
tropis erosa (Quoy and Gaimard, 1832) from Guam," but Omphalotropis suturalis was described from Guam
that species was not found on Rota. O. cookei is closest and is only known from two populations on Rota. This
morphologically to O. elongatula, on Rota. species appears to be restricted to coastal margins of
Omphalotropis cookei was previously known from forests; both on Guam (pers. obs.) and Rota.
Guam and Saipan (Abbott, 1949). Although this species
was found dead at seven sites, only a single living popula-
OmphalotropisquadrasiMoellendorff, 1894
tion was encountered on Rota. Live animals were collected
Fig. 15
from the undersides of decaying leaves. O. cookei appears
Abbott (1949) redescribed and figured Omphalo-
tohave declined on Rota. tropis quadrasi, then considered a Guam endemic. One
Omphalotropis elongatula Quadras and Moellendorff, 894 fresh O. quadrasi shell was found at one site on Rota.
1
Fig. 9
Omphalotropis "carinate" species complex (species 1-5)
Previously known only from Guam, Omphalotropis
elongatula is closest to O. cookei on Rota (see above). No Seventeen specimens collected as subfossils at two
locations on Rota appear to represent a previously unrecog-
live animals of O. elongatula were found on Rota during
nized species complex characterized by turriculate shells
1994or 1995.
ornamented by a well-developed carina. All of the species
Omphalotropis laevigataQFiuga.dr1a0s and Moellendorff, 1894 baepepneacroltloecbteedunodnesGcuriabmedtoanddaten.oTshpeeyciceosullidkeretphreesmenhtavaen
Omphalotropis laevigata was described from Guam. endemic radiation of assimineids on Rota. They are tenta-
Shells which nearly match figured specimens from Guam tively included in Omphalotropis on the basis of Thiele's
(Zilch, 1967) were found at As Matmos Cliffside Cave on (1929: 172) definition of the genus: "Shell oval to turricu-
Rota. late, with perforated umbilicus, surrounded by a more or
less distinct ring; aperture oval, apertural margin in most
Omphalotropisocthogyra Quadras and Moellendorff, 1894 cases interrupted, occasionally somewhat broadened." At
Fig. 1 presentfive species are recognized, but as material toevalu-
Previously known only from Guam, Omphalotropis ate variation is limited, this number might have to be
octhogyra was abundant as subfossils at one site on Rota. revised in the future. All five putative species possess the
Many O. octhogyra shells collected at this site appeared to generic characters mentioned by Thiele except apertural
be fresh (still covered with periostracum). At this site only characters cannot be resolved in all specimens due to their
one land snail species was found alive (Georissa elegans), poorpreservation.
65 1
8 AMER. MALAC. BULL. 12(1/2) (1996)
Table2. Distribution andcollection statusofeach species foundon Rota. F, subfossil collection; FL,collectedboth subfossil andlive; L,collected
alive.
SITENUMBER
SPECIES 1 2 4 6 7 8 10 1 12 17 20 21 24 25
Georissaelegans F F F F
G.laevigata F FL L L L FL F F FL FL L
Palainataeniolata F F L L F F F F F FL L
Truncatellidae F F p L
?Allepithemasp. 1 L F L
Omphalotropiscookei F F L F F F p
O.elongatula F F F F p p
O. laevigata p
O.octhogyra p
0.scwicostulata p p
O.cf.submafitima p
O.suturalis FL p p L
O.quadrasi p
0.sp. 1 p p
O.sp.2 p p
O.sp.3 p
O. sp.4 p
0. sp. p
O. sp. p p L p p p
0. sp.7
Paludinellaconica PL p L L L F p p p p p L
Quadrasieilaclathrata F
?0 sn 1 F
Pythiascarabaeus F F F F F F F F
Pacificella ?variabilis FL F F
Lamcllideasubcvlindrica F F F F F F L
Elasmiasquadrasi FL F F FL F F FL L
Gastrocoptasp(p). F F F F F F F
Nesupupasp(p). F F
Partulagibba F F L L F FL F F F F FL FL
P.cf./aff.gibba F F
Samoanafragilis L
Goniaxiskibweziensis F
Sublinaoctona EncounteredatmanysitesaroundRota.
Succineasp(p). F F F F F F F
Achatinafulica EncounteredatmanysitesaroundRota.
Himeroconchasp. 1 F F
H.sp.2 F
Semperdonheptaptychius F F
S.sp. 1 F
Charopidsp(p.)indet. F F F
Liardetiasp(p.) FL L FL F FL F FL FL L
Lamprocyslissp(p.) FL F L F F F F F L
?Genus?species F
BAUMAN: LAND SNAILS OF ROTA 19
Omphalotropis sp. 1 most abundant and widespread assimineid on Rota. Living
Fig. 16 specimens occurred at five sites and were noted as common
Shell small, globose, and with carina not reaching at many locations by U. S. Fish and Wildlife Officers on
the apex. Known from 1 1 specimens from excavation at Rota. They were also found as subfossils at seven other
sites 12 and 20. sites.
Omphalotropis sp. 2 Genus Quadrasiella Moellendorff, 1894
Fig. 17 Quadrasiella was erected by Moellendorff in
Shell similar to Omphalotropis sp. 1 but slightly Quadras and Moellendorff (1894b) for two species of land
larger with a higher, thinner spire. Known from one speci- snails on Guam; Moellendorff (1900) described a third
men each from excavations at sites 12 and 20. species from Pohnpei (Caroline Islands). Quadrasiella is
differentiated from other assimineids by its operculum,
Omphalotropis sp. 3 which has an "inner calcareous lamella which overlaps the
Fig. 18 peristome" (Moellendorff, 1900: 119).
Shell high spired, cyrtoconoid (with convex sides);
suture channeled with a somewhat prominent carina. Site Quadrasiella clathrata Moellendorff, 1894
20yielded two specimens from excavations. Fig. 25
This species, previously known only from Guam,
Omphalotropis sp. 4 was figured by Zilch (1967). On Rota it was found in exca-
Fig. 19 vations at site 20.
Shell slightly smaller and similar to Omphalotropis
sp. 3, high spired, cyrtoconoid, with carina not as promi- ?Quadrasiella sp. 1
nent. One specimen was collected from excavation at site Fig. 24
20. ?Quadrasiella sp. 1 is conchologically similar to Q.
clathrata from Guam. It differs from Q. clathrata in that
Omphalotropis sp. 5 the body whorl does not expand as fast, the spire is higher,
Fig. 20 and the sculpture is more prominent. No opercula were
Shell close to Omphalotropis sp. 4 but the carina is found in association with the new specimens, thus its
near the middle of a whorl. Known from one specimen generic status is uncertain. This species is known only from
from excavation at site 20. Rota.
PULMONATA
Subclass
Omphalotropis sp. 6 OrderARCHAEOPULMONATA
Fig. 21 Family ELLOBIIDAE
Omphalotropis sp. 6 is conchologically close to O. Genus Pythia Roding, 1798
elongatula and O. cookei on Rota and to O. erosa (Quoy Pythiascarabaeus (Linne, 1758)
and Gaimard, 1832) from Guam. O. sp. 6 was found living Pythia scarabaeus ranges widely on islands in the
under limestone rubble in the forest, but not on the under- western Pacific. Shells of this species are a highly visible
sides ofdecaying leaves. They were moderately abundant. component ofthe ground shell paleofauna in many forested
areas on Rota. No living animals were found. Bishop
Omphalotropis sp. 7 Museum records indicate that the species was common
Fig. 22 alive on Rota in 1925 and 1949 (BPBM 213232, 213261,
This species was only found at Pona Point living and 82427). Subsequently P. scarabaeus has declined and
sympatrically with Omphalotropissuturalis and a truncatel- could be extirpated on Rota.
lid. It is similar in shell shape to O. suturalis but differs by
being finely ribbed. Of the three species found at Pona OrderSTYLOMMATOPHORA
Point, O. sp. 7 is the rarest in my collections. Family ACHATINELLIDAE
GenusPacificella Odhner, 1922
GenusPaludinella Pfeiffer, 1841 Pacificella ?variabilis Odhner, 1922
Paludinella conica (Quadras and Moellendorff, 1894) Fig. 26
Fig. 23 Species of Pacificella are widely distributed on
Paludinella can be separated from the similar genus Pacific islands and were recorded from the Mariana Islands
Assiminea Fleming, 1828, by the absence of a fine spiral without specific locality data (Cooke and Kondo, 1961;
threadjustbelow the suture (Abbott, 1949). P. conica is the Preece, 1995). Its wide range indicates it could have been
20 AMER. MALAC. BULL. 12(1/2) (1996)
4*
12
15
16
^
4
4
20
19
Figs.3-20.LandsnailsfromRota. Sitenumbersforeach speciesarefromFig. 2andarelistedafterthespeciesname. 3.Georissaelegans,20. 4.G.laevi-
gata,20. 5.Palainataeniolata, 12. 6.Truncatellidaesp.,3. 7.lAllepithemasp. 1,6. 8.Omphalotropiscookei,S. 9.O.elongatula, 1. 10.0. laevigata, 12.
11.0.octhogyra, 26. 12. O.semicostulata,20. 13.0.cf.submaritima, 12. 14.0.sutralis,25. 15.0.quadrasi,21. 16.0. 'carina' sp. 1,20. 17.0. 'cari-
na' sp. 2,20. 18. 0. 'carina' sp. 3,20. 19. 0. 'carina' sp. 4,20. 20. O. 'carina' sp. 5, 20. Scalebars= 1 mmexceptFig. 4=2 mm. Fig. I scalebaralso
refers to Figs. 4, 5, and 10. Fig. 6scale baralsorefers to Figs. 12-14and 18-20. Fig. 8 scalebaralsorefers to Figs. 9, 11, and 15. Fig. 16 scale baralso
referstoFig. 17.
1
BAUMAN: LAND SNAILS OF ROTA 21
introduced aboriginally onto the Mariana Islands. Live ani- Nesopupa on Rota were found at the Bishop Museum (e.g.
mals were found at one site on Rota, on the undersides of BPBM 82202, 82429), indicating that live specimens were
tree leaves. collected in 1925 by H. G. Hornbostel. The wide range of
many Nesopupa species are indicative of human transport.
GenusLamellidea Pilsbry, 1910 Specific identificationofthis material was not made.
Lamellidea microstoma (Quadras and Moellendorff,
1894) Family PARTULIDAE
Cooke and Kondo (1961) reviewed this species. It GenusPartula Ferussac, 1821
was not encountered during the present surveys. It was fig- Partulagibba Ferussac, 1821
ured by Zilch (1962). Fig. 31
Partula gibba is endemic to the Mariana Islands,
Lamellideasubcylindrica (Quadras and ranging from Guam through the northern Mariana Islands
Moellendorff, 1894) (Kondo, 1970). This was a widespread species on Rota at
Fig. 27 one time attested by the large numberofsubfossils found at
This species is known only from Guam and Rota almost all sites visited and the large number oflive-collect-
(Cooke and Kondo, 1961). Cooke and Kondo (1961) noted ed specimens housed at the Bishop Museum. Only five of
this to be a less abundant species than Lamellidea micros- the sites surveyed now support living populations of P.
toma on both Guam and Rota. The second species of gibba, indicating that this species has declined greatly in
Lamellidea known in the Marianas (L. microstoma) was not recent years. A similar decline for P. gibba was document-
found on Rota in 1994 or 1995. Live animals of L. sub- ed by Hopperand Smith (1992) on Guam.
cylindrica were collected from the undersides of tree
leaves. Partula cf./aff. gibba Ferussac, 182
Fig. 32
Genus ElasmiasPilsbry, 1910 Four shells of a distinctive Partula were collected
Elasmiasquadrasi (Moellendorff, 894) from paleontologic test pits at Payapai and As Matmos
1
Fig. 28 caves. They are close in general shell shape to P. gibba, but
This species is distinguished from other achatinel- differ in having an extremely thickened and heavy shell.
lids on Rota by its small size (ca. 2.5 mm length) and dis- Similar shells were not mentioned in Crampton's (1925)
tinct apertural barriers. Elasmias quadrasi is known from monograph on variation in Partulidae of the Mariana
Guam, Rota,Tinian, and Saipan and extendsonto the north- Islands. Limited material leaves the status of these shells
ern Mariana Islands (Cooke and Kondo, 1961). Live ani- uncertain; they could represent an extinct undescribed
mals were found aestivating on the undersides ofleaves and (sub)species or local race ofP. gibba.
twigs in trees.
Genus Samoana Pilsbry, 1909
Family PUPILLIDAE Samoanafragilis (Ferussac, 1821)
Genus GastrocoptaWollaston, 1878 No shells of this species were found in 1995.
Gastrocopta sp(p). Bishop Museum records indicate Samoanafragilis once
Fig. 29 occurred on Rota, on the Sabana in 1959 (BPBM 213164-
Gastrocopta is a wide-ranging genus that apparently 213168). Today the Sabana area has been mostly converted
was in part distributed by humans (Solem, 1959, 1988). No into agricultural fields and no living partulids were found
living specimens were found on Rota. Records at the there in 1995. During a short field trip in 1996 to Rota, a
Bishop Museum indicate a species of Gastrocopta was colony of5.fragilis was found at site 24.
alive on Rota in 1949 (BPBM 213220, 213221).
Family STREPTAXIDAE
GenusNesopupa Pilsbry, 1900 Genus GonaxisTaylor, 1877
Nesopupa sp(p). Gonaxis kibweziensis (Smith, 1894)
Fig. 30 This species was introduced to Rota probably from
Australian Nesopupa were reviewed by Solem Aguijan where it was released as a possible control agent
(1988). No live Nesopupa were found on Rota in 1995. forAchatinafulica. Shells ofthis species were found at site
Nesopupa (Nesopupa) quadrasi quadrasi (Moellendorff, 2. I know of no further information about this species on
1894) was described from Guam. A few records of live Rotaotherthan it was alive in 1969 (Eldredge, 1969).
22 AMER. MALAC. BULL. 12(1/2) (1996)
Figs. 21-40. LandsnailsfromRota. Sitenumbersforeach speciesarefromFig.2andarelistedafterthespeciesname. 21. Omphalotropissp.6, 6. 22.O.
sp. 7, 25. 23.Paludinellaconica, 24. 24.IQuadrasiella sp. 1, 20. 25. Q. clathrata, 20. 26.Pacificella ?variablis, 20. 27.Lamellideasubcylindrica,20.
28.Elasmiasquadrasi,20. 29.Gastrocoptasp(p)., 12. 30.Nesopupasp(p)., 1. 31.Partulagibba,8.32.P. cfVaff.gibba, 20. 33.Succineasp(p)., 13. 34.
Himeroconchasp. 1,20. 35.W. sp.2,20. 36.Semperdonheptaptychius, 1. 37.5. sp. 1,20. 38.Liardetiasp(p)., 1. 39.Lamprocystissp(p)., 1. 40.?Genus,
20. Scalebars= 1 mmexcept31,32=4mmand 33 = 3 mm. Fig. 26scalebaralsoreferstoFigs. 29and30. Fig. 22 scalebaralsoreferstoFigs. 23,27,
34-37,and39. Fig.21 scalebaralsoreferstoFigs.25and28. Fig.24scalebaralsoreferstoFigs.38and40.