BiologicalJournal of the Linnean Society (1995),56: 273-307. With 9 figures
Ibe Pitcairn Islands: biogeography, ecology and prehistory
Edited by T. G. Benton and T. Spencer
Systematic review of the land snails of the
Pitcairn Islands
R. C. PREECE
Department of Zoology, University of Cambridge, Downing Street,
Cambridge CB2 3EJ
The land snails (and semi-terrestrial molluscs) of the four islands that comprise the Pitcairn
group are reviewed and the indigenous species illustrated. The strictly terrestrial molluscan
faunas from the two atolls (Oeno and Ducie) are poor, like many other atolls in the Pacific.
Each supports less than six species with wide geographical ranges. In contrast, the terrestrial
molluscan fauna from Henderson Island, an uplifted atoll, is more diverse with at least 16
species belonging to seven families. Over half these taxa appear to be endemic, at least at
the level of sub-species. Two species of semi-terrestrial molluscs have also been found on
Henderson. Analyses of archaeological deposits in caves near the North Beach have revealed
that at least a further six species of land snail formerly occurred on Henderson. The volcanic
island of Pitcaim, the only island in the group still inhabited, supports the greatest number
of terrestrial molluscs. Twenty-six species of land snail (and one semi-terrestrial pulmonate)
were found living there during the recent expedition and a further three taxa were recognized
amongst museum material. At least seven of these species are thought to be recent adventives
and a further three are likely to have been prehistoric introductions. One Henderson (Georissa
hendersont) and three Pitcaim endemics (Pac$cella Jilicq Sinployea pitcairnensis and Diastole
tenuistriata) are formally described as new species. Some of the Pitcairn endemics occur in
very restricted areas (less than a hectare) and it is important that measures should be taken
to prevent the spread of invasive plants, such as rose-apple, that would threaten their survival.
0 1995 The Linnean Society of Iandon
ADDITIONAL KEY WORDS:-land molluscs - Pitcaim Island - Henderson Island - Oeno
Atoll - Ducie Atoll - systematics - endemism - human impact.
CONTENTS
Introduction . . . . . . .
The character ofthe islands
. . .
Sampling sites . . . . . . .
Material examined
. . . . .
Systematic account
. . . . .
Material collected in 1991-92 . .
Additional species present in museum
Insertae sedis . . . . . .
Conclusions . . . . . . .
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0 199.5 The Linnean Society of London
R. C. PREECE
274
Acknowledgements
References
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INTRODUCTION
Knowledge of colonization, evolution and species turnover on remote
oceanic islands has contributed much to theories of island biogeography and
evolution. For terrestrial organisms with no flying or swimming ability the
problems of trans-oceanic dispersal are immense and it is surprising that
such remote islands support any of these pedestrian organisms. This paper
reviews the land snail faunas from one such remote archipelago, the Pitcairn
group, which is situated more than 390 km east of its nearest neighbour,
Temoe Atoll in the Tuamotu-Gambier Islands and 1570 km west of Easter
Island. The fieldwork on which this study is based was undertaken during
the penultimate phase of the Sir Peter Scott Commemorative Expedition to
the Pitcairn Islands in 1991- 1992.
THE CHARACTER OF THE ISLANDS
The four islands that comprise the Pitcairn group, the easternmost
archipelago on the Pacific tectonic plate lying south of the Tropic of
Capricorn, differ markedly in physiography. Ducie (24’39’s 124’48’W) and
Oeno (23’56’s 130’45’W) are small atolls of very different character. Ducie,
the easternmost island in the group about 360 km east of Henderson, is
little more than a large bank of coral rubble, about 4 km in diameter, that
supports only two species of land plant. Oeno is the most western island
and is also about 4 km across but unlike Ducie supports a more diverse
vegetation, including a range of alien plants recently introduced by visiting
Pitcairn islanders. Henderson (24O22’S 128”20’W), the largest island (area 37
km2), is an uplifted atoll with peripheral rims reaching about 33 m as1
surrounding a shallow central depression, interpreted as a former lagoon.
Much of the surface of the island is composed of raised coral limestone
(‘makatea’), now heavily dissected, with pinnacles and crevasses up to 7 m
deep (Spencer & Paulay, 1989). Soils are generally thin and patchy, although
more extensive areas of soil cover occur towards the south. The plateau
supports a dense cover of low native forest and there are varied coastal
plant communities around the lower slopes. It is relatively undisturbed and
only six introduced plants have been recognized (Florence, Waldren &
Chepstow-Lusty, 1995). Pitcairn (25’04’s 130’06’W), by contrast, is a small
(4.5 km’) volcanic island that rises precipitously from the ocean to a height
of 347 m. It was formed between 0.46-0.93 Mya (Duncan et a l , 1975) and
is the southernmost island in the group. Pitcairn is the only island still
inhabited and the habitats have consequently been severely disturbed, although
remnants of the native vegetation remain.
SAMPLING SITES
On each island an attempt was made to cover as wide an area as possible.
Sampling on Henderson was necessarily confined to the trails that had been
PITCAIRN LAND SNAILS
275
cut through the dense vegetation on the plateau and to the areas around
the three beaches. At each site samples were taken from various habitats,
both from the ground-litter and vegetation as well as from the leaves and
trunks of trees. Sieving was employed to ensure the retrieval of small taxa.
Access to the upper slopes of Pitcairn has been facilitated by the construction
of roads following the delivery of a bulldozer in the early 1980s. The
islanders have place-names for every minor topographic feature and I have
used these names, rather than numbers, for my sampling stations (Fig. 1).
All the material was collected alive unless otherwise stated.
The main sampling sites on each island with dates of collection are as
follows. HENDERSON ISLAND. North Beach coastal area and plateau; NorthSouth trail: sites at various intervals, particularly at 530 m and Mid Camp
(several dates Oct-Dec. 1991); Pinnacles trail: area near mid-point (18/12/1991);
North West Point coastal slopes and plateau (27/12/1991); East trail: start and
at mid-point (28/10/1991, 22/12/1991, 24/12/1991); East Beach ferns at base
of cliff (28/10/1991); South Point sites on open coastal plateau (13-15/12/1991).
OENO. Vegetation and ground-litter near camp (3-1 1/ 11/ 1991). PITCAIRN
ISLAND. Adamstown: gardens and vegetation along road to Pulau (l/l1/1991,
5/12/1991); Jack Williams’ Valley: woodland (various dates Nov-Dec 1991);
John Mills’ Valley: woodland and ferns (27/11/1991, 29/11/1991, 4/12/1991);
McCoy’s Valley: woodland and ferns (21-22/11/1991); Brown’s Water: woodland
(17/11/1991, 26/11/1991); Aute Fence: woodland (25/11/1991, 28/11/1991);
Breadfruit VaZley: woodland (23-24/11/1991); Glennis Big Tree: roadside
vegetation and litter (17/11/1991, 25/11/1991); Palua Ridge: ferns and ground
litter (15/11/1991, 2/12/1991); Big Ridge: ferns, litter and tree trunks (2/12/1991);
Eme Fence Valley: cultivated plants (18/11/ 1991); Down Rope: ground litter
(30/11/1991); Dubbin (=Middle Hill): tree trunks (4/12/1991); Tautama: coastal
vegetation (16/11/ 1991); Bounty Bay: under rocks on beach (18/11/ 1991,
26/11/1991); West Harbor: coastal area (19/11/1991).
MATERIAL EXAMINED
The main collections of land snails from the Pitcairn Islands are located
in the following institutions:
Bernice P. Bishop Museum, Honolulu, Hawaii (BPBM). A principal objective
of the Mangarevan Expedition of 1934 was to collect poorly known land
snails from islands in the Tuamotu, Gambier and Pitcairn groups, as well as
from some neighbouring archipelagoes (Cooke, 1935). A large amount of
dry and spirit material was collected by C. Montague Cooke, Jr. and his
assistant Yoshio Kondo during this venture, which has all been deposited at
the Bishop Museum.
Uniuersity Museum of Zoology, Cambridge (UMZC). Apart from a few duplicate
specimens donated to the Bishop Museum, all the land snail material collected
on the Sir Peter Scott Commemorative Expedition has been deposited in
the University Museum of Zoology, Cambridge (R. C. Preece collection).
Natural History Museum, London (BMNH). A few land snails collected on
Pitcairn by Hugh Cuming in 1827-8 and others collected by Lt. J. Walker
276
R.C. PREECE
PITCAIRN LAND SNAILS
277
RN, many years later, have been located in the BMNH. A few additional
shells from Pitcairn, purchased from Mr H. B. Preston, are also present in
the V. W. MacAndrew collection.
National Museum of Wales, Cardaff (NMW). Some material from Pitcairn
Island is present in the Melvill-Tomlin collection (Accession number 1955.
158). This had formerly been in the collection of Col. R. H. Beddome
(1830-191 1).
All the land snail material from the Pitcairn Islands in each of these
institutions has been re-examined as part of this study. The sheer quantity
of specimens in the two main collections in Honolulu and Cambridge has
precluded the listing of the total number of specimens for each species. Such
information is only given for the rarer species.
SYSTEMATIC ACCOUNT
Material collected in 199 7 -92
In the following systematic review a distinction has been made between
taxa found during the recent Expedition in 1991-92 and additional taxa
represented in earlier collections but not recently rediscovered. The systematic
arrangement essentially follows Wenz (1938-40) for the prosobranchs and
Zilch (1959-60) for the pulmonates. The original citation is given for each
species followed by a synonymy that refers only to usage in relation to
material from the Pitcairn Islands.
Prosobranchia
Family Hydrocenidae
Genus Georissa W. Blanford, 1864
Georissa minutissima (G. B. Sowerby, 1832)
Fig. 3A
Cyclostoma minutissimum G. B. Sowerby, 1832: R o c . Comm. Sci. Zool. Soc. Lond.
for 1832, part 11, p. 32.
Hydrocena ? minutissima (Sowerby): Pfeiffer, 1847, Zeitschr. 5 Mal. 4, p. 112.
Leptopoma ? minutissimum (Sowerby): Pfeiffer, 1852, Monographia pneumonopomorum uiventium p. 118.
Georissa minutissima (Sowerby): Thompson & Huck, 1985, i%e Nautilus 99, p.
83.
Material examined. PITCAIRN ISLAND: several lots from Jack Williams’
Valley, John Mills’ Valley, Breadfruit Valley, Brown’s Water, Palva Ridge,
Big Tree T’Malai (UMZC, R. C. Preece coll.); BPBM 141925 (2 shells),
141894 (1 shell).
Remarks. The authorship of this species is ambiguous. The brief diagnosis
appeared as part of a series of descriptions of new taxa by W. J. Broderip
and G. B. Sowerby. Most of these diagnoses bear the initials of either
R. C. PREECE
278
2.0
~
F
0
1.8
0
0
:
0
0
oo
0
0
0
00
:*8
0
I.”
0.9
1.0
1.1
1.2
1.3
1.4
Breadth (mm)
Figure 2. Plot of height versus breadth of shells of Georissu minutissima (0)
from Pitcairn
(John Mills’ Valley) and of Geonksu hendersoni sp. nov. ( 0 ) from Henderson Island
(Fi30 m along N-S trail).
Broderip or Sowerby (sometimes both) but no attribution follows the
description of this taxon, although it follows one for ‘C. succineum’ that is
clearly attributed to Sowerby alone.
Thompson & Huck (1985: 83) first recognised that this species appears to
belong to the genus Georissa, pointing out that the original material consisted
of juvenile shells. The new material, which includes adult shells, has confirmed
this suggestion. This is a much larger species, with a relatively longer spire
(0.49-0.59 of the total height), than Georissa hendersoni (qu) from Henderson
with a mean height of 1.55f0.11 mm and breadth of 1.211 0 . 0 5 mm
( n = 25), compared with 1.20+0.06 and 1.01kO.03 mm ( n = 25), respectively
(Fig. 2). Like the Georissa from Henderson it occurs under stones but could
also be obtained by beating ferns and other plants. It never occurred in the
same high densities as its congener on Henderson. G. minutissima is apparently
known only from Pitcairn Island.
Georissa hendersoni sp. nov
Fig. 3B-F
Georissa sp. Cooke & Kondo, 1961, p. 256.
Georissu sp. nov. Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from all the main
collecting sites on the plateau (UMZC, R. C. Preece coll.); BPBM 149604,
149728, 149747, 149791, 149816, 149820, 149853-4, 149857, 149917, 149949,
149964-5, 150034-7, 150077.
Descr$tion. Shell minute, adults about 1.1-1.3 mm in height and 0.96-1.08
mm in breadth. Colour often a chalky white tinged with pale pink or orange,
particularly in fresh shells. Shell conical with about 3-3.5 whorls separated
PITCAIRN LAND SNAILS
Figure 3. A, Georissa rninutissirna. Pitcairn Island (Jack Williams’ Valley); scale bar = 0.5 mm.
B-F, Geohsa hadersoni sp. nov. B, apertural view of paratype (12040.5~);C, side view of
paratype (120405~);D, sculpture of paratype; E, operculum, internal surface; F, operculum,
external surface. All Henderson Island (530 m along N-S trail), under fragments of coral
limestone. Scale bar = 0.5 mm (B,C); 0.1 mm (D); 0.1 mm (E,F). G-I, Assirninea sp. G, shell;
H, subsutural microsculpture; I, operculum. Henderson Island, cave seeps near NW Point.
Scale bar = 0.5 mm (GJ); 0.1 mm H. J-L, Nesopupa cf. pleurophora. J, Pitcairn Island, Jack
Williams’ Valley; K, L, Henderson Island (530 m along N-S trail); scale bar = 0.5 mm. NP, Nesopupa sp. nov. Henderson Island (530 m along N-S trail); scale bar = 0.5 mm. M,
Q-R, Pupisorna orcula; scale bar = 0.5 mm. Q Pitcairn Island, Jack Williams’ Valley; R,
Henderson Island (530 m along N-S trail); M, apical microsculpture of specimen from
Henderson (scale bar = 0.1 mm). S & T, Pronesopupa sp. S, Pitcairn Island, John Mills’ Valley;
T, Henderson Island (Mid Camp); Scale bar = 0.5 mm.
279
R.C. PREECE
280
by a moderately deep suture. Spire relatively short representing about 0.440.56 of the total height of the shell. Aperture wide and 'D'-shaped, about as
wide as high. The parietal wall lies at an angle of 28-30" to the axis of the
shell, whereas the plane of the aperture is inclined at 30" to shell axis (Fig.
3C). Umbilical area occluded by parietal septum. Apex rounded or very
slightly pointed. Protoconch sculptured by network of fine minute pits.
Sculpture on teleoconch consists of strong spiral threads, best developed on
the upper half of the whorls (Fig. 3D). Growth-lines sometimes enlarged
above shoulder of whorl forming weak ridges along the second and third
whorls. Operculum (Fig. 3E, F) is calcareous, concentric with a large
subcentral nucleus. Inner surface with downwardly curved slender peg
extending beyond the columellar edge of operculum.
Type locality. Henderson Island, limestone plateau behind the North Beach.
Habitat and range. The species was abundant under fragments of coral
limestone, under fallen branches or amongst ground litter over the whole of
Henderson Island.
Holotype. 120405a (UMZC), collected October 5th, 1991 by R. C. Preece.
Paratypes: 120405b-x (24 measured specimens), 120405~-bb(4 gold plated
specimens). Other paratypes: same as material examined.
Dimensions. Measurements (in mm) for the holotype and five paratypes
selected to show variation follow:
height
breadth
~~~
holotype
paratype
paratype
paratype
paratype
last whorl(h)
~
1.16
1.24
1.12
1.24
1.26
I .00
1.00
1.00
1.02
I .oo
~
0.96
1 .oo
0.92
0.98
0.98
aperture(h)
~
~
0.60
0.58
0.52
0.56
0.56
aperture(w)
~
~~
0.62
0.64
0.64
0.64
0.62
Remarks. The genus Georissa is widely distributed in the Pacific from the
Hawaiian Islands westward to Japan, China, Guam and the Philippines, and
southward to tropical Queensland. Eastward it is spread through the Cook,
Society and Pitcairn Islands to the Marquesas.
G. hendersoni is characterized by its minute size, dumpy conical form and
sculpture. It is much smaller than G. minutissima from Pitcairn (see above)
and appears to be smaller than all other described Georissa from the Pacific.
Chondrella striata Pease, 1871 from the Cook Islands is a typical Georissa but
it was described from juvenile shells (Thompson & Huck, 1985). Specimens
of striata in the Bishop Museum are slightly larger and more heavily
sculptured than G. hendersoni. G. obsoleta Thompson & Huck, 1985 from
Vanuatu (New Hebrides) is also similar, but again appears to be slightly
larger, has a taller spire, channelled sutures and different sculpture. Thompson
& Huck (1985) synonymized G. neili Pilsbry, 1928 with G. cookei Pilsbry,
1928 and the status of a third Hawaiian Georissa of similar size is uncertain.
A complete revision of this group is long overdue.
PITCAIRN LAND SNAILS
28 1
Figure 4. A-C, Orobophana soliduh. Henderson Island, North Beach. Scale bar = 1 mm (A,
B); 0.5 mm (C). D-F, Diastole glaucina. North West Point, Henderson Island. Scale bar = 1
mm (D); 0.1 mm (E); 0.5 mm (F). G-I, Diastole tenuistriatu sp. nov: Pitcairn Island, Jack
Williams’ Valley. Scale bar = 1 mm (G, H); 0.5 mm (I).
Family Helicinidae
Subfamily Helicininae
Genus Orobophana A. J. Wagner, 1905
Orobophana solidula (G. B. Sowerby in Gray, 1839)
Fig. 4A-C
Helicina solidula Sowerby in Gray, 1839, p. 146, t. 38, fig. 26.
Orobophana solidula (Gray): Wagner, 1911, pp. 227-228, t. 45, fig. 13; Cooke
& Kondo, 1961, p. 256: Serpell et al., 1983, p.10.
Helicina solidula Gray: Smith, 1913, Ann. Mag. nat. Hist. 12, p. 410.
Material examined. HENDERSON ISLAND: several lots from all main coastal
stations (UMZC, R. C. Preece coll.); BPBM 149410, 149419-25, 149437,
149469, 149509-16, 149577-9, 149598, 149621-30, 149636-8, 149680-1,
149693-705, 149709, 149727, 149743, 149807-15, 149852, 149869, 149916,
150005, 150027, 150033.
Remarks. Most authors have attributed this species to J. E. Gray but this is
incorrect. Captain Beechey had commissioned Gray to describe the
“Molluscous Animals, and Their Shells” collected on the Voyage of HMS
R. C. PREECE
282
T A I ~1.: Frequency of different colour morphs of Orobophana solidula at various sites on
Henderson
Scaeuola scrub
South Point
______
Yellow
Orange-brown
Banded
~~-
166 (59.7Vn)
91 (32.7%)
2 1 (7 5%)
Ground litter
North West Point
~~
~~
72 (57.6Vo)
48 (38.40h)
,5 (4 O'WI)
Under limestone
on plateau
at North Beach
On Phymatosorus
behind East Beach
~
~~
60 (5Fi 5Oh)
44 (40.7Vo
4 (3.7%)
30 (73 IL",)
11 (26 X"h)
0 (O"k0)
Blossom but after 8 years Gray had still failed to produce a finished report.
Beechey therefore asked G. B. Sowerby "to complete the Conchology, and
to revise the unprinted portion of Mr. Gray's MS ..." (Beechey in The
Introduction, viii). Helicina solidula is described on page 146 and illustrated
on t. 38, Fig. 26. O n page 143 it clearly states that "The following notes
relating to such shells as are represented in Plates xxxiii to xliv and not
referred to in the foregoing pages, have been put together.. .by G. B.
Sowerby" (Gray, 1839).
The genus Orobophuna was first separated from other Pacific Island helicinids
and described by Wagner (1905) who listed a range from Fiji, Tonga, Cook,
Niue, Society, Tuamotus, Marquesas and Hawaii. In a subsequent monograph
(Wagner, 1911) he recognized two sub-species of 0. solidula, in addition to
the nominal form (0. solidula solidula) from 'Elisabeth-Insel' (i.e. Henderson
Island). Both of the other sub-species, 0. solidula coloruta (Pease, 1868) and
0. solidula raiateae (Wagner, 1905) from Anaa and Raiatea respectively, are
smaller (breadths about 5 mm, heights about 3 mm) than the form from
Henderson (breadth about 6.5, height about 3.5 mm) and are said to have
stronger spiral sculpture. Many Henderson shells also have strong sculpture
(Fig. 4C), especially when young, so the importance of this character is
uncertain. Wagner's work has been strongly criticized, for example by Solem
(1959: 166-7), and a thorough revision of helicinids throughout the Pacific
is needed before the status of these taxa can be accurately assessed.
This species is common on Henderson, where it occurs under stones or
climbing on trees and other plants. It seems to be confined to coastal areas
extending for only about a kilometre inland and does not live in the centre
of the island. The shell is polymorphic with respect to colour and can be
bright yellow, orange-brown or may have a single peripheral orange-brown
band. The yellow colour morph dominated all the habitats sampled and
occurred at frequencies of 50-75% (Table 1).
Family Assimineidae
Genus Assiminea Fleming, 1828
Assiminea sp.
Fig. 3G-I
Syncera sp. Cooke & Kondo, 1961, p. 256.
Assiminea sp. Serpell et al. 1983, p. 10.
PITCAIRN LAND SNAILS
283
Material examined. HENDERSON ISLAND: areas adjoining North, North
West and East Beaches, coastal area around the South Point (UMZC, R. C.
Preece coll.); BPBM 149411, 149426-7, 149438-45, 149447, 149480-2,
149561-2, 149580-3, 1499599-601, 149639, 149682, 149706, 149710, 1497446, 149870-4, 149902, 150000. PITCAIRN ISLAND: dead shells from Down
Rope (UMZC, R. C. Preece coll.).
Remarks. The specific identity of this species is unknown and must await a
full revision of the genus. On Henderson it occurred in coastal areas under
stones and dead Pandanus and Argusia branches (often with Melampus). It also
occurred on rock faces of the fossil reef slope behind the North Beach; near
the South Point it dominated communities under stones amongst Scaevola on
the cliff top.
Pulmonata
Family Ellobiidae
Genus Allochroa Ancey, 1887
Allochroa layardi (H. & A. Adams, 1855)
Ophicardelus (Laimodonta) layardi H. & A. Adams, 1855, BOG.
Zool. Soc. Lond.,
part XXII, for 1854: 30-37.
Material examined. HENDERSON ISLAND: North Beach (single lot). OENO:
10 dead shells from beach drift (UMZC, R. C. Preece coll.).
Remarks. Identification of this widespread Pacific species has been confirmed
by Dr A. M. F. Martins, who has recently undertaken a systematic revision
of Allochroa and published a detailed account of the anatomy of A . layardi
based on this Henderson material (Martins, 1995). Several of these small
banded shells were found crawling on algal-covered limestone blocks on the
landward side of the reef below high-water level on the North Beach. On
one overcast day in December 1991 they appeared from crevices in great
numbers on the nearby rock promontories, where previous searching had
failed to detect their presence. This pulmonate is included here since the
upper parts of these promontories lie well above high-water level.
Genus Melampus Montfort, 1810
Melampus Jlavus (Gmelin, 1791)
Voluta j a u a Gmelin, 1791 in Linnaeus’ Systema Naturae (13th edition), p.
3436.
Melampus luteus (Quoy & Gaimard, 1832): Smith, 1913, Ann. Mag. nut. Hist.
12, p. 411.
Melampus sp. Cooke & Kondo, 1961, p. 256; Serpell et al. 1983, p. 10.
MelampusJlavus (Gmelin, 1791): Rehder in Fosberg et al. 1983, p. 38.
Material examined. HENDERSON ISLAND: beach-ridge behind North Beach,
one lot, East Beach, (6 shells), North West Beach (several dead shells)
(UMZC, R. C. Preece coll.); BPBM 149711 (7 shells). OENO ATOLL: one
284
R. C. PREECE
fresh shell (UMZC, R. C. Preece coll.). DUCIE ATOLL: 10 shells from
north side of Acadia motu (UMZC, R. C. Preece coll.). PITCAIRN ISLAND:
Bounty Bay (14 shells). Down Rope (16 dead shells), (both UMZC, R. C.
Preece coll.).
Remarks. This widespread Indo-Pacific species has now been confirmed from
all the islands in the Pitcairn group. Most shells were pale yellow, although
three uniformly dark brown shells were found on Henderson. O n Pitcairn,
one dark brown shell with three narrow white bands was collected under
stones (with the common yellow forms) near the landing at Bounty Bay, and
at Down Rope two brown and two banded shells were found amongst the
dominant yellow morphs. On Henderson M. Jlauus was found amongst shingle
or under wood and leaves of Pandanus or Argusia on the beach-ridge near
the first promontory on the North Beach towards the NE Point. Living
specimens were also observed in rock crevices on the promontory itself, at
levels slightly above those occupied by A. layardi.
Family Achatinellidae
Subfamily Pitysinae
Genus Tubuaia Cooke & Kondo, 1961
Tubuaia fosbergi Kondo, 1962
Fig. 5N, 0
Tubuaia fosbergi Kondo, 1962, pp. 19-20.
Material examined. PITCAIRN ISLAND: Jack Williams’ Valley, John Mills’
Valley, McCoy’s Valley, Palva Ridge, Brown’s Water, Glennis Big Tree, Big
Ridge, Tautama (all UMZC, R. C. Preece coll.); BPBM 135141 (holotype),
10138-9, 135142-4, 13546-7, 141871: BMNH 84-11.20.101-10 (pars) as
Zamillidea [sic] perplexa Garr.’ coll. J. Walker.
Remarks. This endemic species is distinct by virtue of its large size (length
4.6 mm, breadth 2 mm), coarse sculpture, deep sutures and shouldered
whorls (Fig. 5N, 0).It was previously known from just 14 specimens (only
three of which were adult) from dead Pandanus leaves at Middle Hill and
from the north slope behind Adamstown. In 1991 it was found in great
numbers on bare soil and amongst ground-litter at several sites on the upper
slopes.
Tubuaia hendersoni Kondo, 1962
Fig. 5R, S
Tubuaia hendersoni Kondo, 1962, pp. 36-38; Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from all main
collecting stations (UMZC, R. C. Preece coll.); BPBM 10132 (holotype),
10133-5, 149392, 149413, 149415, 149432-3, 149466-8, 149475-6, 1495367, 149553-4, 149586-7, 149645-6, 149718, 149721, 149736-7, 149739,
149762-3, 149765, 149767-8, 149770, 149796-7, 149801, 149838, 149839aC, 149865, 149881-3, 149905, 149913, 149921, 149940, 150046, 150083.
PITCAIRN LAND SNAILS
Figure 5. Achatinellidae from the Pitcairn Islands. Scale bar = 1 mm (unless otherwise stated).
A-C, Lamellidea oblonga. A, Pitcairn (St. Paul’s); B, Henderson (530 m along N-S trail); C,
Oeno. D & E, Lamellidea sp. D, Henderson (530 m along N-S trail); E, Oeno. F & G,
Lamellidea cf. micropleura. F, Pitcairn (John Mills’ Valley); G, Henderson (530 m along N-S
trail). H-J, Pacificella variabilis. H & J, Henderson (530 m along N-S Trail); I, Oeno. K,
Pacificella sp. Henderson (ii30 m along N-S trail). L & M, Paa$cella$lica, sp. nov. L, adult;
M, juvenile. Pitcairn. Both from Davallia ferns on Palva Ridge, N & 0, Tubuaia fosbergi. N,
adult; 0, juvenile, both Pitcairn (Jack Williams’ Valley). P & Q, Tubuaia voyana christiani. P,
adult; Q juvenile, Pitcairn. both St. Paul’s, R & S, Tubuaia hendersoni. R, adult; S, juvenile,
both Henderson (530 m along N-S trail). T, Tornatellides oblongus oblongus. Pitcairn, (Glennis
Big Tree). U, Tornatellides oblongus paruulus. Henderson (530 m along N-S trail). V & W,
Elasmias sp. V, adult shell; W, microsculpture of same shell (scale bar = 0.1 mm), Pitcairn
(Jack Williams’ Valley). X & Y, Elasmias sp. Henderson (start of trail to East Beach)
285
286
R. C . PREECE
Remarks. This Henderson endemic is a ground-dwelling species, that frequently
occurs at high densities under dead Pandanus leaves or under limestone
blocks.
Tubuaia voyana christiani Kondo, 1962
Fig. 5P, Q
Tubuaia voyana christiani Kondo, 1962, pp. 34-35.
Material examined. PITCAIRN ISLAND: several lots from all main collecting
sites (UMZC, R. C. Preece coll.); BPBM 10152 (holotype), 10153, 135138,
135148-51, 137607, 138562, 141873, 141875, 141879, 141902a-12, 141928,
141969-71, 141978-83, 142115-25, 142132, 142135-44, 163204; BMNH ACC.
No 2228 (as ‘T. peponum Gould’), 84.11.20.101-10 (pars), 8 shells (as ‘L.
oblonga Pse’), both J. Walker coll.
Remarks: Kondo (1962) separated this sub-species from T. v. voyana because
of differences in the parietal lamella, which in christiani is prominent (in
adults) and strongly sinuous and bent inwards, whereas in voyana it is usually
weaker and less strongly inflected. This is a common species both on the
ground and climbing ferns and other plants.
Subfamily Pacificellinae
Genus Pacijicella Odhner, 1922
PaczJicella variabilis Odhner, 1922
Fig. iiH-J
Pacificella variabilis Odhner, 1922, Natural History of Juan Fernandez and Easter
Island 3(2), p. 249, pl. 8, figs. 15-17.
‘Tornatellinops variabilis’ (Odhner): Cooke & Kondo, 1961, pp. 172-5; Serpell
et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from all main
collecting stations (UMZC, R. C. Preece coll.); BPBM 142031-2, 148538-41,
149394-8, 149400, 149402-6, 149452-3, 149487-9, 149508, 149544, 149547,
149557, 149566-8, 149588-90, 149592, 149612-7, 149633, 149635, 149678,
149753-4, 149779, 149798, 149817, 149824-6, 149841-3, 149845, 149890-3,
149909, 149930, 149955-6, 149968-9, 149979, 149990-2, 150012-6, 150024,
150026, 150058-9, 150061, 150063-4, 150072, 150079, 150084. OENO:
several lots (UMZC, R. C. Preece coll.); BPBM 150092-4, 1,50098-100,
150102, 150105-9, 150112, 1.501 14, 150116-7, 150119-22, 150125-39, 1501412. DUCIE: 2 shells (UMZC, R. C. Preece coll.). PITCAIRN ISLAND: several
lots from collecting stations in and around Adamstown (UMZC, R. C. Preece
~011.); BPBM 141887, 141919-20, 142126.
Remarks. Cooke & Kondo (1961) included this species in the genus Tornatellinops
but variabilis Odhner is the type species of Pacificella and must therefore
revert to this genus. Next to Elasmias, Pacijicella is the most widespread genus
in the family and P. variabilis has the widest individual range (Cooke &
PITCAIRN LAND SNAILS
287
Kondo, 1961; figs 77, 78). This species has been recorded from Easter Island
in the east to Truk in the Carolines in the west. Many of these islands have
distinct forms or sub-species of P. variabilis. Examples from the Pitcairn
Islands are illustrated in Fig. 5H-J. The widespread occurrence of this species
has been attributed to human dispersal since it is commonly associated with
cultivated plants. On the Pitcairn Islands it was abundant on various plants,
including ferns, and on Pitcairn itself it was found on both the native and
introduced vegetation.
Pacificella Jilica, sp. nov.
Fig. ;5L, M
Material examined. PITCAIRN ISLAND: Palva Ridge (44 shells), McCoy’s
Valley (12 shells), John Mills’ Valley (6 shells), Glennis Big Tree (3 shells),
Jack Williams’ Valley (1 shell) (UMZC, R. C. Preece coil.); BPBM 138563
(1 shell), 163202 (2 shells).
Rescr$tion. Shell moderately large, (mean height 3.59 _+ 0.1 1 mm; mean
breadth 2.10 +0.07 mm, n= 13), broadly conical, reddish-brown, thin and
translucent. Surface has dull gloss, faintly covered with growth-lines. Spire
tapering to a distinctly pointed apex. Sutures moderately deep and whorls
convex. Whorls 4.5-5.0. Body-whorl large, swollen, rounded below, nearly
three-quarters (71%) of the height of the shell. Aperture large, ear-shaped,
outer margin rounded. Peristome thin, simple. Parietal lamella weakly to
moderately developed (proportionately more strongly developed in juvenile
specimens), perpendicularly seated and relatively short, extending for about
a quarter of a whorl. Columella sigmoid and strongly twisted, inner face
with slight swelling in middle part. Palatal wall without teeth.
Type locality. Palva Ridge, Pitcairn Island.
Holotype. 122870a (UMZC), collected 2/12/1991 by R. C. Preece; Paratypes,
as material examined.
Dimensions. Measurements (in mm) for the holotype and paratypes from the
type locality (see Cooke & Kondo, 1961, fig. 3 for methods of measurement):
height
~
holotype
paratype
paratype
paratype
paratype
paratype
paratype
paratype
paratype
paratype
paratype
paratype (BPBM 16320!2)*
3.60
3.76
3.48
3.72
3.48
3.76
3.56
3.64
3.52
3.40
3.64
3.64
breadth
-~
2.04
2.12
2.04
2.20
2.00
2.20
2.12
2.00
2.08
2.12
2.16
2.20
*precise locality on Pitcairn not given
last whorl(h)
-
aperture(b) apert. axis whorls
~
2.60
2.68
2.52
2.68
2.44
2.72
2.56
2.56
2.52
2.48
2.56
2.60
1.20
1.28
1.20
12 0
1.20
1.20
1.20
1.20
1.20
1.20
1.20
1.20
1.52
1.68
1.64
1.76
1.44
1.60
1.60
1.60
1.56
1.56
1.60
1.68
5
4.5
4.5
fi
4.5
4.75
4.5
4.75
4.75
4.5
4.75
4.75
288
R. C . PREECE
Remarks. This species is readily separated from other ‘tornatellinids’, with
which it occurs, by virtue of its larger size and pointed apex. It was found
on ferns (Davallia solida) and taro leaves at five sites on Pitcairn. It appears
to be endemic. Associated species at its type locality included Tubuaia voyana
christiani, T. fosbergi, Nesopupa cf. pleurophora and Philonesia jiliceti.
Genus Lamellidea Pilsbry, 1910
Lamellidea (Lamellidea) cf. micropleura Cooke & Kondo, 1961
Fig. 5F, G
Lamellidea (Lamellidea) micropleura Cooke & Kondo, 1961, pp. 193-196.
Lamellidea cf. micropleura Cooke & Kondo: Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: North Beach (dead shells in
ground litter on beach-ridge); 530 m from the plateau behind the North
Beach along N-S trail (also at Mid Camp), along East Trail; BPBM 149755,
149667, 149741, 149848, 149898-9, 149947. PITCAIRN ISLAND: Brown’s
Water, Breadfruit Valley, Jack Williams’ Valley, Big Ridge, John Mills’
Valley, Middle Hill.
Remarks. L. micropleura was originally described from a few specimens collected
at very different elevations on Moorea, in Faatoai Valley (type locality) and
on Mount Teaharoa. The holotype (BPBM 150531) is similar to specimens
from the Pitcairn Islands but is slightly smaller and has a smoother shell.
Very few adult shells from Moorea are available for comparison and the
specific attribution of the material from the Pitcairn Islands is therefore
provisional. All the specimens from Moorea were found under loose bark
or lichens growing on trees. It occurred in precisely these habitats on both
Henderson and Pitcairn, where it could be found in considerable numbers.
Occasional specimens were also found in chinks in coral limestone (Henderson)
or in small cavities in blocks of lava (Pitcairn).
Lamellidea (Lamellidea) oblonga (Pease, 1865)
Fig. 5A-C
Tornatellina oblonga Pease, 1865, R o c . Zool. SOC.Lond. for 1864, part 111: p.
673.
Tornatellina (Lamellina) oblonga Pease: Pilsbry & Cooke, 1915 Manual of
Conchology 23: pp. 160-165, pl. 36, figs. 5, 6, 8-1 1; pl. 41, figs. 6, 9, pl. 42,
figs. 7-10.
Lamellidea oblonga (Pease): Cooke & Kondo, 1961, pp. 196-209, Serpell et al.
1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from all the main
collecting sites (UMZC, R. C. Preece coll.); BPBM 149388-90, 149412,
149418, 149431, 149446, 149463, 149473-4, 149494-5, 149533, 149611,
149640-2, 149683, 149716-7, 149733-5, 149740, 149752, 149759-61, 149794,
149818-9, 149829, 149837, 149844, 149856, 149860-4, 149879-80, 149903-
PITCAIRN LAND SNAILS
289
4, 149918-20, 149953, 149960, 149967, 149972, 150001-3, 150008-10,
150044-5. OENO: several lots (UMZC, R. C. Preece coll.); BPBM 150140,
150095-7, 150101, 150103-4, 150110-1 1, 150113, 150115, 150118, 150123,
150136, 150143. PITCAIRN ISLAND: Eme Fence Valley, Glennis Big Tree,
Jack Williams’ Valley, Aute Fence, Tautama (UMZC, R. C. Preece coll.);
BPBM 141977, 142114; BMNH 84.11.20.101-10 (pars), 2 shells, J. Walker
coll.
Remarks. This is an extremely common species which can occur at high
densities (several hundred specimens can be found under a single log). On
Henderson it was especially common in coastal areas, where it occurred
under dead Pandunus, coconut and other plants and also under rotten logs
on the plateau. It was abundant in similar habitats on Oeno and Pitcairn.
According to Cooke & Kondo (1961) L. oblonga is essentially a common
lowland species that becomes scarce west of the 165th meridian. It has
undoubtedly been transported with food plants by the early Polynesians and
its relative scarcity west of the 165th meridian may be due to the fact that
migration between the Cook and Society Islands and the islands of Samoa
and Tonga was infrequent.
Lamellidea sp.
Fig. 5D, E
Material examined. HENDERSON ISLAND: several lots from all the main
collecting sites (UMZC, R. C. Preece coll.); BPBM 149407 (pars), 149477-8,
149555, 149595, 149632 (pars), 149654-7, 149659, 149726, 149738, 149764,
149766, 149769, 149777 (pars), 149780, 149784, 149786, 149790, 149799,
149849-50 (pars), 149884, 149927, 149937, 149961-3, 149984, 149995,
150031-2, 150078, 150085. PITCAIRN ISLAND and OENO: several lots
from all the main collecting sites (UMZC, R. C. Preece coll.).
Description. Shell brownish-yellow, long, thin, cylindrical with gradually tapering
spire. Surface glossy faintly marked with growth-lines. Apex somewhat obtuse.
Whorls 4.25-4.75, somewhat flat, separated by rather shallow suture. Bodywhorl large, representing about 65% of the total height. Base of shell rather
flattened. Aperture small and oval, outer lip simple and rather straight.
Columella lightly thickened, nearly vertical or only slightly sinuous. Parietal
lamella weakly to moderately well developed, extending for about half a
whorl.
Dimensions (in mm). Total height 2.72*0.15; height of last whorl 1.78*0.11;
total breadth 1.44 0.08; apertural diameter 0.76 f0.05; apertural axis
1.04+0.08 ( n = 28).
Remarks. This shell differs from L. oblonga, with which it commonly occurs,
by its smaller shell, shorter spire, composed of less than five whorls, and
proportionately larger body-whorl. The whorls are also flatter and the base
of the shell less convex. It has a more cylindrical shell than PaciJcella
variubilis, with which it also occurs, and has shallower sutures and less convex
290
R. C. PREECE
whorls. This species is common on various herbaceous plants at many sites
on Henderson and elsewhere. Its specific identity is uncertain.
Subfamily Tornatellininae
Genus Elasmias Pilsbry, 1910
Elasmias sp.
Fig. 5V-Y
Elasmias sp. Cooke & Kondo, 1961, p. 256; Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from the start of East
Trail; various sites all along the N-S trail and on Pinnacles trail (UMZC, R.
C. Preece coll.); BPBM 149449, 149483-7, 149531-2, 149607, 149610,
149675-7, 149836, 149971, 150021-3. PITCAIRN ISLAND: many lots from
plants bordering road in Adamstown, Eme Fence Valley, Aute Fence, Jack
Williams’ Valley, John Mills’ Valley, Palva Ridge, Big Ridge, Brown’s Water
(UMZC, R. C. Preece coll.); BPBM 135153, 141949-54, 141963-7, 163201.
OENO: BPBM 150124.
Remarks. According to Cooke & Kondo (1961: 219-222, fig. 96) Elasmias is
the most widespread of the ‘tornatellinid‘ genera, a fact which must partly
be due to human agency as it is easily dispersed with cultivated plants. It
is an arboreal genus which can be found on the underside of leaves of
plants such as Pisonia and Nesoluma (Henderson) and on the leaves of various
cultivated plants on Pitcairn (coconut, taro, banana, ginger, Cordyline). No
specimens were found on Oeno in 1991 but a note accompanying the single
example (BPBM 150124) collected there by the Mangarevan Expedition said
that it occurred on Polypodium [ = Phymatosorus]. Several specimens from
Pitcairn are relatively large and globose and have fine, close spiral striae
(Fig. 5W) and resemble E. apertum (Pease, 1865). The Henderson specimens
are narrower (Fig. 5, X, Y) and have a deeper suture, stronger parietal
lamella and narrower columellar plate. Their specific identity is uncertain. It
is noteworthy that fossil specimens of Elasmias, apparently identical to the
modern Henderson form, occurred below the main Polynesian occupation
horizon in one of the caves (Hen-6) behind the North Beach, demonstrating
that it is not a recent arrival to this island.
Subfamily Tornatellidinae
Genus Tornatellides Pilsbry, 1910
Tornatellides (Tornatellides) oblongus oblongus (Anton, 1839)
Fig. 5T
Strobilus oblongus Anton, 1839, Verzeichniss der Conchylien, 46.
Tornatellides oblongus (Anton): Pilsbry & Cooke, 1915, Manual of Conchology
23: p. 198, pl. 44, fig. 13.
Tornatellides (Tornatellides) oblongus oblongus (Anton): Cooke & Kondo, 1961,
p. 248-255.
Material examined. PITCAIRN ISLAND: several sites in Adamstown, Jack
PITCAIFW LAND SNAILS
29 1
Williams’ Valley, McCoy’s Valley, John Mills’ Valley, Big Tree T’Malai,
Glennis Big Tree (UMZC, R. C. Preece coll.); BPBM 141889-93, 141923-4,
141947-8, 141955-62.
Remarks. This species occurs on most of the high islands in the south-east
Pacific from Nukuhiva (lat. 8’52’s) in the north to Rapa (lat. 27’36’s) and
from Pitcairn (long. 130’06’W) in the east to Rarotonga (long. 159’46’W) in
the west (Cooke & Kondo, 1961). It is essentially a lowland species generally
found “at altitudes of a few feet above high water mark on the flat just
back from the beach to about 200 feet” (Cooke & Kondo, 1961: 251). On
Pitcairn it was widespread and occurred on the ground under rotting leaves
of Pandanus, coconut, breadfruit and banana.
Tornatellides (Tornatellides) oblongus paruulus Cooke & Kondo, 1961
Fig. 5U
Tornatellides (Tornatellides) oblongus parvulus Cooke & Kondo, 1961, pp. 255256; Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: 530 m from the North Beach
rim along N-S trail, also at Mid Camp and at 8100 m; BPBM 149408-9,
149479, 149507, 149558-61, 149742, 149782, 149787-9, 149804-6, 149851,
149900-1, 149914-5, 149939, 149948, 149997-9, 150069, 150074-6, 150080,
150086.
Remarks. Shells of T. 0. paruulus are much smaller than those of T. 0. oblongus.
Mean heights and breadth are 2.47f0.13 and 1.54&0.06 mm for the former
( n = 25) and 3.06f0.12 mm and 1.82f0.08 mm ( n = 13) for the latter.
Measurements of these forms from Pitcairn and Henderson reveal a clear
separation with minimal overlap (Fig. 6), although Cooke & Kondo (1961)
3.4
3.2
1
0
0
0
t
0 0
0
0
0 0
0 0
2.2 I
1.4
0
1
1.6
,
I
1
1.8
Breadth (mm)
I
2.0
2.2
Figure 6. Plot of height versus breadth of shells of Tornatellides oblongus. (0)
T. o. oblongus
from Adamstown, Pitcairn and ( 0 ) T. o. parvulus, 530 m along the N-S trail, Henderson
Island.
292
R.C. PREECE
did wonder whether the size difference might be ecophenotypic. This is the
only representative of the genus Tornatellides known from a non-volcanic
island south of the equator and was the only form that Cooke & Kondo
thought merited separation as a possible sub-species.
Family Pupillidae
Subfamily Nesopupinae
Genus Pupisoma Stoliczka, 1873
Pupisoma orcula (Benson, 1850)
Fig. 3M, Q R
Helix orcula Benson, 1850, Ann. Mag. nut. Hist. 2(vi), p. 251.
Pupisoma sp. Cooke & Kondo, 1961, p. 256.
Pupisoma cf. orcula (Benson, 1850): Serpell et al. 1983, p. 10
Material examined. HENDERSON ISLAND: several lots from each of the
main collecting stations (UMZC, R. C. Preece coll.); BPBM 149026-8, 149448,
149517-22, 149528-9, 149584, 149605-6, 149674, 149714, 149732, 14974950, 149793, 149821, 149827-8, 149835, 149875-7, 149950-2, 149970, 150007,
150039-41. PITCAIRN ISLAND: several lots from each of the main collecting
stations (UMZC, R. C. Preece coll.).
Remarks. Specimens from the Pitcairn Islands compare well with material of
this species in the Benson collection (UMZC) which are probably syntypes.
This species has a closed umbilicus and a characteristic apical sculpture (Fig.
3M), which compares well with illustrations of Australian specimens published
by Solem (1988; figs 21-23). On both Henderson and Pitcairn, specimens
could be found under leaves or under loose bark and lichen. Specimens
were also frequent at the extremities of thin branches and occasional
specimens occurred under fallen branches.
P. orcula has a wide range and is known from South Africa, India, Japan,
Indonesia, New Guinea, Hawaii (Pilsbry, 1922-6: 228), Australia (Solem,
1988) and there are other records as close as Makatea in the Tuamotus
(Pilsbry, 1927-35: 116).
Genus Nesopupa Pilsbry, 1900
Nesopupa cf. pleurophora (Shuttleworth, 1852)
Fig. 3J-L
Pupa pleurophora Shuttleworth, 1852, Bern. Mittheil. p. 296.
Nesopupa cf. pleurophora (Shuttleworth, 1852): Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several batches from all the main
sites on the plateau (UMZC, R. C. Preece coll.); BPBM 142025, 149462,
149730-1, 149757, 149792, 149832-4, 149855, 150038, 150081. PITCAIRN
ISLAND: Adamstown, Jack Williams’ Valley, Brown’s Water, Big Tree
T’Malai, Palva Ridge, Breadfruit Valley, John Mills’ Valley, Middle Hill (all
UMZC, R. C. Preece coll.); BPBM 141897 (2 shells).
PITCAIRN LAND SNAILS
293
Descrz$tion. The shell is dark reddish-brown and covered with a series of
coarse, irregular periostracal ribs. Apex has a granular microsculpture. There
are eight (or occasionally up to 10) apertural barriers. Angular and parietal
barriers are strongly developed, the latter turned inward. A small subparietal
can sometimes be seen set further back in the roof of the aperture. There
is a moderately strong columellar fold turned up as its end and a weak
subcolumellar tooth that is not always visible from direct frontal view. Upper
and lower palatals are subequal, not long and converge inwardly. The end
of upper palatal is sharply downturned. There may be one or two interpalatals
which are both much smaller and there is a small tubercular suprapalatal.
Remarks. This species was common and generally found climbing trees or
other plants, although it occasionally occurred under fallen branches. The
shells from the Pitcairn Islands match descriptions and specimens of N.
pleurophora from Tahiti and the Marquesas Islands.
Nesopupa sp. nov.
Fig. 3N-P
Nesopupa sp. nov. Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: several lots from all the main
collecting stations (UMZC, R. C. Preece coll.); BPBM 142024, 149430,
149471-2, 149527, 149603, 149715, 149748, 149758, 149831, 149859, 149985,
150006, 150028.
Remarks. This is a smaller species than N. pleurophora and has a paler,
smoother shell that lacks the coarse periostracal ribbing. There are fewer
apertural barriers: single strong parietal and angular folds, (the former turned
slightly inward), a moderately strong columellar tooth, and upper and lower
palatal barriers. The former is peg-like, whereas the latter is a lamella fold
that extends further into the mouth. A weak interpalatal is sometimes visible.
This appears to be an undescribed species known only from Henderson,
where it was common under blocks of limestone and from ground litter.
Unlike N. pleurophora it was not found climbing trees. A full description will
be published elsewhere.
Subfamily Vertigininae
Genus Columella Westerlund, 1878
cf. Columella sp.
Material examined. OENO: single dead shell (UMZC, R. C. Preece coll.)
Remarks. A single juvenile shell is tentatively attributed to this genus. It was
found in a sample of beach-drift from the edge of the lagoon. The genus
has a holarctic range and is also known from Hawaii but has not been
confirmed from elsewhere in Polynesia.
294
R. C . PREECE
Genus Pronesopupa Iredale, 1913
Pronesopupa sp.
Fig. 3S, T
Material examined. HENDERSON ISLAND: single lot from under lichen on
tree at Mid Camp, dead shell from 400 m along Pinnacles trail. PITCAIRN
ISLAND : Aute Valley, Brown’s Water, Breadfruit Valley, John Mills’ Valley,
Palva Ridge, Big Ridge, Middle Hill, Adamstown (all UMZC, R. C. Preece
coll.).
Remarks. The genus Pronesopupa has not previously been reported from the
Pitcairn Islands, although it is known from the Kermadec, Marquesas and
Hawaiian islands (Pilsbry, 1920-1). In general, the Pitcairn specimens have
more distinct periostracal spines than those from Henderson (Fig. 3S, T) but
otherwise they are similar and probably conspecific. They are similar to P.
boettgeri spinigera Pilsbry from Hawaii but are slightly larger than the holotype
(BPBM 11031) of that sub-species. Pronesopupa was especially common on
Pitcairn where it occurred on both lichen-covered and smooth-barked trunks
of various trees including rose-apple (Syqgium jambos).
Family Subulinidae
Subfamily Subulininae
Genus Subulina Beck, 1837
Subulina octona (Bruguiere, 1792)
Bulimus octonus Bruguiere, 1792, Encycl. Meth. Vers 1, p. 325.
Material examined. PITCAIRN ISLAND: Breadfruit Valley, John Mills’ Valley,
Glennis Big Tree, West Harbor (UMZC, R. C. Preece coll.); BPBM 141974-6.
Remarks. A common circumtropical species that is almost certainly introduced
on Pitcairn.
Genus Opeas Albers, 1850
Opeas pumilum (Pfeiffer, 1840)
Bulimus pumilus Pfeiffer, 1840, Arch. Naturges. 1840, p. 252.
Material examined. PITCAIRN ISLAND: Adamstown, Breadfruit Valley, Jack
Williams’ Valley, West Harbor, Brown’s Water (UMZC, R. C. Preece coll.);
BPBM 138568-70, 141973, 141984.
Remarks. This species has been widely introduced from its home in the
American tropics and now occurs on many islands in the Pacific. Almost
certainly a modern introduction to Pitcairn.
Genus Allopeas H. B. Baker, 1935
Allopeas clavulinum (Potiez & Michaud, 1838)
Bulimus clavulinus Potiez & Michaud, 1838, Gall. Moll. Douai 1, 136, pl. 14,
figs 9, 10.
PITCAIRN LAND SNAILS
295
Material examined. PITCAIRN ISLAND: Adamstown, Breadfruit Valley, Jack
Williams’ Valley, Brown’s Water, Radio Station, Tuatama, Down Rope, West
Harbor, McCoy’s Valley (UMZC, R. C. Preece coll.).
Remarks. This species ranges from the Mascarene Islands to Australia, Japan
and Polynesia. It is also common in greenhouses and hot-houses in the
Northern Hemisphere. It is almost certainly a recent introduction to Pitcairn.
Allopeas gracile (Hutton, 1834)
Bulimus gracile Hutton, 1834, J. Asiat. SOC.Bengal 3, 84-5, 93.
Material examined. PITCAIRN ISLAND: Jack Williams’ Valley, Adamstown,
Brown’s Water, McCoy’s Valley (UMZC, R. C. Preece coll.).
Remarks. Literature references to this species are completely unreliable due
to confusion with similar species. Following Naggs (1992) Allopeas has been
raised to full generic rank with A. grucile as its type species. A. gracile is a
synanthropic species with a circumtropical range. Evidence that it was
dispersed by the Polynesian settlers onto Pacific Islands was presented by
Christensen & Kirch (1981: 81) who demonstrated that it was present on
Tikopia, Solomon Islands, as early as 900 BC. Probably a recent introduction
to Pitcairn.
Family Endodontidae
Genus Minidonta Solem, 1976
Minidonta hendersoni Cooke & Solem in Solem, 1976
Fig. 7A-D
Thaumatodon sp. Cooke & Kondo, 1961, p. 256.
Minidonta hendersoni Cooke & Solem in Solem, 1976, pp. 134-135; Serpell et
al. p. 10.
Figure 7. A-D, Minidonta hendersoni. Henderson Island, plateau behind North Beach. Scale
bar = 0.5 mm (A-C); 0.1 mm (D).
296
K.C. I’IIEECE
Material examined. HENDERSON ISLAND: several stations around the North
Beach (living), dead shells around East Beach, North West Point, South Point
(UMZC, R. C. Preece coll.); BPBM 149858 (holotype), 149858 (33 other
shells), 149428-9, 149461, 149470, 149573-4, 149602, 149631, 149707-8,
149712-3, 149728-9, 140756, 149830, 149858.
Remarks. In common with most other endodontids, this is a ground-dwelling
species that occurred under coral limestone or under fallen logs, such as
those of miro (T’espesia populnea). Although dead shells of this Henderson
endemic were widespread over the whole island, including the South Point,
living and fresh shells were only found in the vicinity of the North Beach.
Family Charopidae
Subfamily Charopinae
Genus Sinployea Solem, 1982
Sinployea pitcairnensis, sp. nova
Fig. 8A-C
Material examined. PITCAIRN ISLAND: Jack Williams’ Valley (19 shells),
John Mills’ Valley (9 shells), Brown’s Water (1 shell) (UMZC, R. C. Preece
coll.)*
Descr$tion. Shell discoidal, relatively large (diameter 3.9-4.6 mm), with 4.54.75 normally coiled whorls. Apex and spire slightly and evenly protruded,
upper spire flat, last whorl descending more rapidly. Apical whorls 1.25,
Figure 8. Sinployeu pitcuitnmis sp. nov. Holotype, Pitcairn Island, Jack Williams’ Valley.
Scale bar = 1 mm.
PITCAIRN LAND SNAILS
297
with faint traces of spiral microsculpture. Post-nuclear whorls with prominent,
protractively sinuated rounded radial ribs, 65-85 on the body-whorl, whose
interstices are usually about 5-6 times their width. Ribs/mm 5-10.
Microsculpture of fine radial riblets, 8-10 between each pair of major ribs.
Sutures deep, whorls rounded above, flattened laterally above periphery and
on basal margin. Whorl contour with slight angulation on the periphery.
Aperture ovate, lip simple, slightly deflected above. Umbilicus open, about
a third of the diameter of the shell. Colour light yellow-reddish brown with
darker transverse stripes or flammulations on both apical and umbilical
surfaces.
Type locality. Jack Williams’ Valley, Pitcairn Island.
Holotype. 122670a, collected 2/11/1991 by R. C. Preece. Paratypes: same as
material examined.
Dimensions. Measurements (in mm) and other features of the holotype and
three paratypes from the type locality follow (see Solem, 1976, fig. 5, for
methods):
breadth(b)
holotype
(122670a)
paratype
(126670b)
paratype
(122670~)
PaatYPe
(122670d)
height(h) umbilicus(u) b/u ratio
ribs
ribs/mm
whorls
4.58
1.83
1.66
2.75
81
6
4.75
4.33
2.00
1.41
3.07
72
5
4.25
4.33
2.41
1.33
3.25
76
6
5
3.91
1.83
1.16
3.37
69
6
4.75
Remarks. This species appears to belong to the genus Sinployea, which has
the widest geographical range and greatest number of species for any
Polynesian endodontoid genus, although it has hitherto not been recorded
east of the Society Islands (Solem, 1982). This broad distribution has been
attributed to their usual semi-arboreal habitat which is likely to increase the
chances of dispersal on logs up-rooted during severe storms. The Pitcairn
species did not climb tree-trunks but was found under logs and amongst
ground litter, always at low density.
Family Helicarionidae
Subfamily Microcystinae
Genus Philonesia Sykes, 1900
Philonesia (Pitcairnia) pitcairnensis Baker, 1938
Fig. 9G-I
Helix brunnea Pfeiffer, L. 1848, p. 33; 1868, p. 54 non Anton, 1839.
Philonesia (Pitcairnia) pitcairnensis Baker, 1938, pl. 18, figs 10-1 1; 1940: 109.
Material examined. PITCAIRN ISLAND: McCoy’s Valley (UMZC, R. C.
Preece coll.); BPBM 11322 (holotype), 135125-34; NMW, 26 shells in MelvillTomlin coll; BMNH, 4 broken shells labelled ‘brunnea Anton, Pitcairn’s Island
under dead leaves H. C.’ [Hugh Cuming].
R. C. PKEECE
Figure 9. A-C, ‘Microcystis verticillata Pse’, Pitcairn. Melvill-Tomlin collection (NMW, Acc. No.
55.158). D-F, ‘Mimucystis aurulenta Beck‘. Pitcairn. Melvill-Tomlin collection, Acc. No. 7383
(ex R. H. Beddome coll.). G-I, Philonesia pitcairnensis, Pitcairn, Holotype (BPBM 11322). J-L,
PhiZonesia filiceti, Pitcairn. J, unbanded yellow morph; K, hyaline banded; L, two-banded
morph. M-0, Philonesia sp. Pitcairn (BPBM 164802 pars).
PITCAIRN LAND SNAILS
299
Remarks. Pfeiffer (1848, p. 33 and 1868, p. 54) listed ‘Helix brunnea Anton’,
a taxon originally described from South America, from Pitcairn Island based
on material in the Cuming collection. This attribution is most improbable
and re-examination of the Cuming shells in the Natural History Museum
suggests that they are immature shells of P. pitcairnensis. Pfeiffer (1848, p.
33) lists ‘Helicopsis glandula Beck‘ in the synonymy of H. brunnea, whereas
Baker (1940: 174) does the converse, listing H. brunnea in the synonymy of
‘Hiona ? (Minorbis 3) glandula’ (qv.). Both these taxa probably refer to P.
p itcairnensis.
Baker (1940) proposed P. pitcairnensis as the type species of the sub-genus
Pitcairnia. P. pitcairnensis has a dark brownish horn-coloured shell quite
different from the larger and highly coloured shell of P. jiliceti. It was less
common than P. jiliceti and recently only immature shells were found amongst
ground litter and on ferns at one site. Given its frequency in past collections,
it may have become rare in recent years, although the season of collection
might be important.
Philonesia (Pitcairnia) jiliceti (Beck, 1837)
Fig. 9J-L
[Nanina] Microcystis jiliceti Beck, 1837, Index: 2 (nude) Nanina jiliceti Beck,
Nov. sp.: 3.
Helix adamsii Pfeiffer, L. 1845, Proc. 2001.SOC.Lond. for 1845, part XIII, p.
66 (in part);
Helix adamsi Pfeiffer, L. 1848-77. Monographia Heliceorum Kventium 3: p. 33;
4: p. 13; 5 : p. 54; 7: p. 65.
Nanina adamsi (Pfeiffer) Tryon, 1886, Manual 2: 112, pl. 37, figs 22-25.
Helix ornatella (Beck) Pfeiffer, 1848, Monogr. 1: 32 (in part), Conch. Cab. 1:
234, pl. 29, figs 23-26.
Material examined. PITCAIRN ISLAND: Jack Williams’ Valley, John Mills’
Valley, McCoy’s Valley, Palva Ridge, Glennis Big Tree, Aute Fence, Breadfruit
Valley (UMZC, R. C. Preece coll.); BPBM 106221, 11323, 135101-21,
135140, 135152; NMW, two lots in Melvill-Tomlin coll. One labelled ‘jilicetz’
(18 shells), another labelled ‘Microcystis adamsi Pfr’ (2 shells ex R. H. Beddome
coll.); BMNH Acc. No. 1563, 5 shells in V. W. MacAndrew coll. labelled
‘Microcystis ornatella’, said to come from Opara [i.e. Rapa].
Remarks. This highly polymorphic species possesses a shell that can be
unbanded (yellow), hyaline-banded (diffuse white bands), mid-banded, twobanded or four-banded (fig. 9J-L). The ground colour is always yellow. As
with many banded snails, fusions of adjacent bands can also occur to give
a predominantly dark-coloured shell. One particularly striking morph has
both white and brown subsutural bands. There are sharp differences between
the banding frequencies at neighbouring sites (Table 2). This species could
be found climbing on the leaves of banana and Cordyline and also ferns
(Davallia solida).
Baker (1940) has pointed out that Cuming appears to have mixed his
specimens of Microcystis ornatella from Rapa and his Pitcairn shells of P.
jiliceti. Several museum specimens of P. jiliceti from Pitcairn are consequently
R. C. PREECE
300
TAR~.E
2. Banding polymorphism in the shells of Philonesia Jiliceti at two sites on Pitcairn
Jack Williams’ Valley
~
~~
~~~
28
31
0
20
1
0
Yellow (unbanded)
Mid-banded
Four-banded
Hyaline banded
Two brown bands
Two brown and one white band
~~
(3.5.0(%1)
(38.75%)
(O(/o)
(25.Onio)
(1.25%)
(O‘RI)
Palva Ridge
~
~
~~~~~~~~~~~
7 (26.%?%)
1 (3.84oh)
7 (26.Y’Wn)
0 (0%)
0 (O(YI1)
11 (42.3VlJ)
labelled ‘M. ornatella’, which is known only from Rapa (Baker, 1938: 61). In
the case of the MacAndrew material in the BMNH, I suspect that the
converse has also happened. P. filiceti appears to be endemic to Pitcairn
Island.
Genus Diastole Gude, 1913
Diastole glaucina Baker, 1938
Fig. 4D-F
Diastole glaucina Baker, 1938, p. 50, pl. 17, fig. 7; Cooke & Kondo, 1961, p.
256; Serpell et al. 1983, p. 10.
Material examined. HENDERSON ISLAND: North West Point, 4 live juvenile
shells (UMZC, R. C. Preece coll.); BPBM 11400 (holotype), 142011-23,
149966, 150018-20.
Remarks. The shell is superficially similar to immature shells of Orobophana,
the only other shell of this size (5-6 mm) on Henderson, but is much more
delicate and tightly coiled, always dark reddish-brown, with a sharper
peripheral keel and completely different sculpture (Fig. 4D-F). Unlike most
of the other Henderson endemic snails, D. glaucina does not appear to be
widely distributed over the island at present. Indeed living specimens were
only found on lichen-covered tree trunks on the plateau a short distance
inland from the North West Point. This is precisely the same locality where
it was originally found by the Mangarevan Expedition on June 21, 1934.
Fossil specimens were collected in pre-Polynesian occupation levels in a cave
(Hen-6) behind the North Beach.
Diastole tmuistriata sp. nov.
Fig. 4G-I
Material examined. PITCAIRN ISLAND: Jack Williams’ Valley (2l), McCoy’s
Valley (2l),John Mills’ Valley (as), Big Tree T’Malai (1 shell), (UMZC, R.
C. Preece coll.).
Descr$tion. Shell thin, light-horn coloured, rather small (3.3-4 mm), somewhat
depressed, trochiform, with rounded apex and sharply keeled periphery.
Whorls 4.25-4.5, separated by relatively shallow suture. Apical whorls with
PITCAIRN LAND SNAILS
30 1
spiral threads intersecting fine radial riblets. These become progressively
stronger and more regular after the 2nd whorl so that on the 3rd whorl
there are about 80 riblets/mm. The spiral threads are of minor importance.
In later whorls the sculpture is weaker. Aperture quite narrow and sharply
angulate. Columella has only an indistinct thickening. The umbilicus is
narrow and little more than a chink. The umbilical surface is lightly flattened
and covered with a series of wavy sub-parallel spiral lines (about 8jO.l mm).
Dimemions
height (mm)
~
Holotype (122675a)
Paratype (122675b)
~
diameter (mm)
~
2.36
2.24
~~~
4.00
3.56
whorls
-
4.5
3.5
Type locality. McCoy’s Valley, Pitcairn Island.
Holotype. 12675a collected 21/11/1991 by R. C. Preece. Paratypes: same as
material examined.
Remarks. This species was found amongst ground litter at four sites on
Pitcairn. Many of the shells were not fully grown and it was not possible to
measure more adult shells. It differs from D. conula (Pease), a widespread
species in parts of the Pacific, in its smaller size, less distinct columellar
thickening and apical microsculpture. It is also smaller than D. glaucina and
the shell is fawn-coloured, rather than reddish-brown, and the microsculpture
is dominated by radial, rather than spiral elements (Fig. 41).
Family Zonitidae
Subfamily Vitreinae
Genus Hawaiia Gude, 1911
Hawaiia minuscula (A. Binney, 1840)
Helix minuscula Binney, 1840, J Boston SOC.N.H. 3, p. 435.
Hawaiia minuscula (A. Binney): Baker, 1941, pp. 322-323.
Material examined PITCAIRN ISLAND: Jack Williams’ Valley, Radio Station,
Brown’s Water, McCoy’s Valley (UMZC, R. C. Preece coll.); BPBM 135137,
138558-61, 141870, 141895-6, 141968, 163200. OENO: single lot (UMZC,
R. C. Preece coll.).
Remarks. Apparently native in the nearctic region but widely spread by
humans throughout Europe and the islands of the Pacific including the
Pitcairn Islands.
Subfamily Gastrodontinae
Genus Zonitoides Lehman, 1862
Zonitoides (Zonitellus) arboreus (Say, 1817)
Helix arboreus Say, 1817, Nich. Encycl., pl. 4, fig. 4.
Material examined. PITCAIRN ISLAND: site at western end of Adamstown,
under rotting vegetation (UMZC, R. C. Preece coll.).
302
R. C. PREECE
Remarks. Appears to be native over the entire nearctic region and extends
into the tropics where it can often be abundant in moist, acid woodland.
Widely introduced as a greenhouse alien in Europe. Almost certainly
introduced on Pitcairn.
Family Limacidae
Genus Deroceras Rafinesque, 1820
Deroceras sp.
Material examined. PITCAIRN ISLAND: several sites in Adamstown, Brown’s
Water, John Mills’ Valley, Jack Williams’ Valley, near Radio Station, Glennis
Big Tree (UMZC, R. C. Preece coll.).
Remarks. Externally these slugs resemble the common European species D.
reticulatum but they were smaller and greyer. Internally they approached D.
laeve but they were far larger than is usual for this species. The specific
identity remains uncertain. No examples of any slugs from Pitcairn were
present in the spirit collections made by the Mangarevan Expedition in 1934
and preserved in the Bishop Museum, Honolulu. It would therefore appear
that these are recent introductions.
Additional species present in museum collections
The following taxa are represented in museum collections but were not
rediscovered on the recent Expedition.
Hiona (Minorbis) verticillata (Pease, 1868)
There are three shells from Pitcairn labelled ‘Microcystis verticillata Pse’ in
the NMW (Melvill-Tomlin coll. Acc. No. 55.158). These have a pale glassy
shell (about 4.5 mm in diameter) with a depressed spire composed of about
4 whorls, rounded periphery and no umbilicus (Fig. 9A-C). Pease’s (1868:
228) original description of Nanina verticillata from Moorea suggests a similar,
but slightly larger, shell to the Pitcairn specimens, but it has not been
possible to make critical comparisons with type material.
‘Microcystis aurulenta Beck, 1852’
Specimens from Pitcairn bearing the above name are represented in the
BMNH, two shells in the V. W. MacAndrew coll. Acc. No. 1563 and two
shells in the NMW in the Melvill-Tomlin coll. (Acc. No. 7383 ex Col. R.
H. Beddome). Both batches represent the same taxon which has a light
brown shell about 5 mm in diameter, with a depressed spire, bluntly keeled
periphery and no umbilicus (Fig. 9D-F). Faint spiral sculpture is visible near
the apex. Baker (1940), tentatively listed ‘Helix aurulentu Pfeiffer, 1853’ in the
synonymy of Philonesia jiliceti, but this is clearly an unrelated taxon.
Philonesia sp.
There are two Philonesia shells from Pitcairn in the Bishop Museum that
are neither P. pitcairnensis nor P. jiliceti. One (BPBM 106222) is labelled
‘Microcystis ? adami’, the other is in a pill-box with a typical P. jiliceti (164802
PITCAIRN LAND SNAILS
303
pars) which is labelled ‘Mic.tis ornatella, Fulton coll.’. It is readily separated
from P. Jiliceti by its more conical shape and by its less expanded body
whorl (Fig. 9M-0). Both specimens have two brown bands, one above, the
other below the periphery. The ground colour is pale yellow. This may well
represent an undescribed species but in view of the muddles that have
occurred with some museum Philonesia, confirmation of its occurrence on
Pitcairn is required.
Incertae sedis
There are a few references in the literature to species that are said to
come from Pitcairn. I have been unable to trace any examples of these and
their status requires confirmation.
Pupa Pfeezfferi Boettger, 1881’
Boettger (1881, pp. 68-9, taf. XII, fig. 18) describes and figures a new
pupillid from Pitcairn. The figure does not seem to be a Nesopupa but appears
to be more like a Gastrocopta.
Alaea pitcairnensis Beck and Alaea millium Beck
Listed in Beck’s Index Molluscorum p. 85 from Pitcairn Island. Names and
locality only (nomina nuda).
Hiona ? (Minorbis ?) glandula (Beck, 1837)
Baker (1940: 174) repeats Beck‘s description and reviews all that is known
of this taxon. It might be synonymous with P. pitcairnensis (see earlier
comments).
‘Nanina’ margarita Albers, 1860
Baker (1940: 335) gives a translation of Albers’ description. Nothing further
is known.
CONCLUSIONS
This is the first comprehensive survey of the land snails from the Pitcairn
Islands. Previous studies have been largely concerned with the systematics
of individual families including the Helicinidae (Wagner, 191l), ‘Zonitidae’
(Baker, 1938, 1940, 194I), Achatinellidae including ‘Tornatellinidae’ (Cooke
& Kondo, 1961; Kondo, 1962) and Endodontidae (Solem, 1976). Fosberg,
Sachet & Stoddart (1983) provided a provisional faunal list from Henderson
Island and a slightly more detailed one was given by Serpell et al. (1983)
in their submission to the Foreign and Commonwealth Office when a
proposal to construct an airstrip there was under discussion. Revised faunal
304
R. C. PREECE
lists from each island, together with assessments of the status of each species
are given in Table 3.
The terrestrial molluscan faunas from the two atolls in the group are poor,
like so many others in the Pacific. Only six species of land snail and two
species of semi-terrestrial molluscs (Melampus flauus and Allochroa layardi) are
known from Oeno, whereas Ducie supports only M. flavus and a single
species of ‘Pacijicella’. With the exception of the Columella from Oeno, all
are widespread Polynesian species.
The land snail faunas from the two other Pitcairn islands are much more
diverse, but again have distinct Polynesian affinities. During this survey at
least 16 species of land snails (and two semi-terrestrial pulmonates) have
been recognized on Henderson Island. Most are pulmonates, belonging to
four different families, but three prosobranch families occur, each represented
by single species. About half (-44%) of these land snails are endemic, at
least at the level of sub-species. This figure may rise because further
taxonomic work is likely to reveal the presence of one or two additional
species of Achatinellidae. Paulay (1991) suggested that all the indigenous land
snails on Henderson were endemic but this is certainly an over-estimate.
Analysis of archaeological deposits in caves behind the North Beach
indicates that at least a further six species of land snail formerly occurred
on Henderson. These cannot be matched with any living species and they
are likely to be extinct endemics eliminated at the time of the Polynesian
occupation between 400-900 yr BP (R. C. Preece & M. I. Weisler, unpublished
data). Other evidence suggests that some snails, such as Diastole glaucina and
Minidontu hendersoni, which today have restricted distributions on Henderson,
once occurred over larger areas of the island. D. glaucina co-existed with the
extinct taxa in the North Beach area, whereas M. hendersoni apparently
occurred over the whole island. It is tempting to link the contraction of
their ranges with the period of Polynesian occupation, although further
evidence is needed.
Additional species of Achatinellidae are also likely to be found on Pitcairn
where twenty-six species of land snail (and one semi-terrestrial pulmonate)
were recorded during the recent Expedition. These are again mostly
pulmonates but two prosobranch families, each with single species, also occur.
Eight of these land snail species appear to be endemic. An additional three
taxa from Pitcairn were recognized in museum collections, which may include
further endemic species. At least seven species of land mollusc from Pitcairn
are thought to be recent adventives (Table 3) and at least three others
(Lamellidea oblonga, Pacijicella uariabilis and Pupisoma orcula) are likely to have
been prehistoric introductions. These three species also occur on Henderson,
but this island lacks any modern introductions (e.g. Hawaiia minusculu and
subulinids), such as occur on Pitcairn. The status of five other taxa mentioned
in the literature from Pitcairn remains uncertain.
It is interesting to note a symmetry in the distribution of certain land
snails on Henderson and Pitcairn providing examples of inter-island speciation.
Endemic species of Georissa, Tubuaia and Diastole occur on each island,
although it is not clear whether these represent sister species such as Paulay
(1991) has suggested for the sub-species of Tornatellides oblongus. Baker (1941:
349) speculated that Diastole glaucina, the only known endemic ‘zonitid’ from
PITCAIRN LAND SNAILS
30.5
TAH1.t: 3. Synoptic list of the land snails and semi-terrestrial molluscs from the Pitcairn Islands.
E = endemic, MI = modem introduction, PI = prehistoric introduction, W = widespread,
? = status uncertain.
Henderson
~~~
E
E
E
W
W
W
E
E
E
PI?
W?
W?
W
?
PI?
E
W
E
PI?
W?
E
?
E?
MI
MI
MI
MI
E
E
E
E
?
?
E
E
E?
MI
MI
MI
~
~~
~
~~
~~~~~~
~
Subclass Prosobranchia
Hydrocenidae
Georissa minutissima (G.B. Sowerby, 1832)
Geonksa hendersoni, sp. nov.
Helicinidae
Orobophana solidula (G.B. Sowerby in Gray, 1839)
Assimineidae
Assiminea sp.
Subclass Pulmonata
Ellobiidae
Allochroa layardi (H. & A. Adams, 1855)
Melampus j l u u u s (Gmelin, 1791)
Achatinellidae
Tubuaia hendersoni Kondo, 1962
Tubuaia fosbergi Kondo, 1962
Tubuaia uoyana christiani Kondo, 1962
Lamellidea oblonga (Pease, 1865)
Lamellidea cf. micropleura Cooke & Kondo, 1961
Lamellidea sp.
Elasmias apertum (Pease, 1865)
Elasmias sp.
‘Pacificella uariabilis’ (Odhner, 1922)
Paajixella flica, sp. nov.
Tornatellides oblongus oblongus (Anton, 1839)
Tornatellides oblongus paruulus Cooke & Kondo, 1961
Pupillidae
Pupisoma orcula (Benson, 1850)
Nesopupa cf. pleurophora (Shuttleworth, 1852)
Nesopupa, sp. nov.
cf. Columella sp.
Pronesopupa sp(p).
Subulinidae
Subulina octona (Bruguiere, 1789)
Opeas pumilum (Pfeiffer, 1840)
Allopeas clavulinum (Potiez & Michaud, 1838)
Allopeas gracile (Hutton, 1834)
Endodontidae
Minidonta hendersoni Cooke & Solem in Solem,
1976
Charopidae
Sinployea pitcairnensis, sp. nov.
Helicarionidae
Diastole glaucina Baker, 1938
Diastole tenuistriata, sp. nov.
‘Microcystisaurulenta Beck, 1852’
‘Hiona verticillata (Pease, 1868)’
Philonesia filiceti (Beck, 1837)
Philonesia pitcairnensis Baker, 1938
Philonesia sp.
Zonitidae
Hawaiia minuscula (Binney, 1840)
Zonitoides arboreus (Say, 1816)
Limacidae
Deroceras sp.
Pitcairn
Oeno
Ducie
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~
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a
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*
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*
a
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*
*
*
*
*
a
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*
*
*
*
a
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a
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a
a
a
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a
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306
R. C. PREECE
a relatively low non-volcanic island, “may be only a local mutation of D.
conula”. There are no examples of intra-island speciation with the possible
exception of Philonesia on Pitcairn, where two (or maybe three) congeneric
species occur. The paucity of local speciation in the two main islands in the
Pitcairn group may result from a combination of their relatively small size
(Pitcairn), topographic uniformity (Henderson) and young age (both are only
0.5-1 Myr old).
The human impact on Pitcairn has been severe and it is possible that
other endemic taxa may once have occurred there. The non-calcareous nature
of this island, unlike Henderson, makes it unlikely that deposits containing
fossil land snails will ever be discovered there to establish whether this was
the case. Some of the endemic species described here from Pitcairn (Sinployea
pitcairnensis, PaciJicella Jilica and Diastole tenuistriata) survive only in small
remnants of the native vegetation that now cover areas no more than a
hectare or so in extent. These species are currently under severe threat from
the spread of invasive plants, such as the rose-apple, which cast a deep
shade and create an understorey which is inimical to these taxa. It is
important that appropriate measures are taken to ensure the survival of this
native vegetation and its associated molluscan fauna.
ACKNOWLEDGEMENTS
Robert Cowie, Graham Oliver, Fred Naggs and Peter Mordan helped me
examine the collections in their care. Fred Naggs also checked the
identifications of the subulinids, Antonio M. Frias Martins confirmed the
Allochroa, Brian Eversham checked the Deroceras and Beata Pokryszko dissected
some of the pupillids. Gustav Paulay and Robert Cowie commented on an
earlier version of the paper. Special thanks are due to Bill Lee and Ray
Symonds for technical help and to John Rodford who drew Figure 8.
My visit to the islands as part of the Sir Peter Scott Commemorative
Expedition was generously supported by the following major sponsors: The
Royal Society, International Council for Bird Preservation, British
Ornithologists’ Union, J. A. Shirley, Foreign & Commonwealth Office UK,
UNESCO, The Leverhulme Trust and Percy Sladen Memorial Fund. This is
paper 43 of the Sir Peter Scott Commemorative Expedition to the Pitcairn
Islands.
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