OCCASIONAL MOLLUSCAN PAPERS 2008 1: 1 – 5. ISSN 1793-8708 (print edition) Date of Publication: 8 th October 2008 ISSN 1793-8716 (online edition) © molluscan.com Chan et al.: New Species of Amphidromus from Rotti Island 1 ON A NEW SPECIES OF AMPHIDROMUS (SYNDROMUS) (GASTROPODA: PULMONATA: CAMAENIDAE) FROM ROTTI ISLAND, INDONESIA Chan, Sow-Yan*, Tan, Siong-Kiat** & John B. Abbas*** * VBox 888313, Singapore 919191. Email: chansowyan@gmail.com **Raffles Museum of Biodiversity Research, Blk 6, Science Drive 2, Singapore 117546. Email: dbstsk@nus.edu.sg *** Blok D- 2, No 10, Sunter Garden, Sunter, DKI, Jakarta. Email: john123abba@yahoo.com ABSTRACT A new species of polymorphic and colourful arboreal snail belonging to the family Camaenidae is described from Rotti Island (off southwestern end of Timor), southeastern Indonesian Archipelago. Amphidromus (Syndromus) rottiensis new species is diagnosable using shell morphology and geographically close congeners of the subgenus Syndromus, namely A. (S.) contrarius Müller, 1774 and A. (S.) poecilochrous Fulton, 1896 are used for comparison. The new species being described here appears distinct enough to justify a specific status, and suggests an ancestral affiliation closest to A. (S.) contrarius and A. (S.) poecilochrous. KEYWORDS Systematics, taxonomy, Gastropoda, Camaenidae, Amphidromus, Syndromus, subgenus, new species, Rotti, Samau, Timor, Lesser Sunda Islands, Nusa Tenggara, Indonesia. INTRODUCTION The Camaenidae is a large and diverse family of terrestrial snails with more than a hundred known genera (Vaught, 1989) occurring in tropical Australasia and the Americas (Abbott, 1989). The Syndromus, a subgenus of Amphidromus, evolved and radiates into some of the most colourful and distinctive forms in the Lesser Sunda Islands of eastern Indonesia. Based on the checklist of Laidlaw & Solem (1961), A. (S.) contrarius was the only recorded Syndromus from Rotti Island. Primarily, A. (S.) rottiensis can be differentiated from A. (S.) contrarius by the lack of a small calloused nodule on the parietal wall near the posterior angle of the aperture (see Laidlaw & Solem, 1961; Pilsbry, 1900). The three colour forms (patterned, unpatterned and pink) of A. (S.) rottiensis within an isolated population demonstrates a classic example of the intra-population variability concept. MATERIALS AND METHODS Geologically, Rotti Island (=Pulau Rote) of 1214 square kilometers is located about 20 kilometers southwest of the southwestern end of Timor, belonged to the Australian continental plate, and of limestone in origin (Monk et al., 1997). Sawu, Rotti, Samau (=Pulau Semau) and