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Members of the terrestrial snail family Dyakiidae from Southeast Asia show a distinct geographical distribution pattern and possess different degrees of complexity in their amatorial organ gland. This study is the first molecular phylogeny of ten of the 12 genera in this family, performed to provide insights into the origin of Dyakiidae and the evolution of their shells and amatorial organ gland structure. A new genus and new species, Pseudoquantula lenticularis Jirapatrasilp & Panha gen. & sp. nov., was uncovered based on its distinct morphological characters and molecular divergence. All other genera were retrieved as monophyletic except for Dyakia. Mainland Southeast Asia was inferred to be the ancestral range of the Dyakiidae, and the lineages then dispersed to and diversified in Borneo. Cladistic analysis showed that all 14 morphological characters used in this study were homoplastic. These results disagree with the previous amatorial organ transformation series, in which neither Pseudoplecta nor Quantula was ancestral to the other genera. The enigmatic genus Pseudoplecta, which lacks an amatorial organ gland, exhibited secondary loss.

Ampullariidae include the largest of all freshwater snails and are of ecological, evolutionary and anthropogenic importance in Southeast Asia (SEA). Native ampullariids belonging to the genus Pila face various threats but are understudied, with their species taxonomy being confused and data on their distributions being scarce. We provide a comprehensive update on the nomenclature, status and distribution of Pila species in Thailand, based on DNA barcoding and geometric morphometric analysis of recently collected material. We confirm that at least five Pila species are extant in Thailand: Pila virescens, P. celebensis, P. turbinis, P. gracilis and P. pesmei. Pila celebensis, which has distinctive egg masses among all the known Southeast Asian Pila, appears to be sister to a clade comprising other SEA and some African Pila. Our results suggest that Pila may have dispersed into SEA on at least two separate occasions. Two singletons collected from northern and eastern Thailand may constitute separate species, but this requires further study. Intraspecific diversity of the mitochondrial cytochrome c oxidase subunit I gene was relatively high for P. celebensis, P. gracilis and P. pesmei (maximum uncorrected p-distances varied from 7% to 9%), and may include cryptic species. Conversely, P. virescens showed low intraspecific p-distances (c. 0%) among clades collected from different localities. This strongly suggests that introductions by humans may be the major cause of this pattern, and our own observations—we found that this species is being cultured and is commonly sold in markets for human consumption—are consistent with this. Pila turbinis was the rarest species, with live snails being collected from only two localities. Throughout Thailand, invasive confamilial Pomacea species appear to be replacing native Pila species, particularly in the Chao Phraya basin. While Thai Pila exhibit surprisingly high genetic diversity, with cryptic species likely being present, widespread invasive snails pose a major threat to their survival and urgent conservation action is needed.

The Streptaxoidea are an ancient and species diverse group that is poorly understood. Examination of the reproductive anatomy of Diaphera showed it to be notably distinct from that of most other streptaxid genera but to exhibit similarities with the reproductive anatomy of Sinoennea (Enneinae), Careoradula (Strepaxinae), Discartemon (Strepaxinae), Augustula (Strepaxinae), and a species of Imperturbatia (Gibbinae). Our molecular phylogenetic analysis placed the two genera with high-spired shells, Sinoennea and Diaphera, in an isolated position as a sister group to the Streptaxidae sensu stricto. This basal divergence within the Streptaxoidea provides support to the proposed recognition of a new family, the Diapheridae. None of the genera possessing low-spired shells, Careoradula, Discartemon, Augustula, and Imperturbatia, were available for inclusion in the molecular analysis and we therefore provisionally restrict the Diapheridae to Diaphera and Sinoennea. However, based on their reproductive anatomy Careoradula, Discartemon, Augustula and a species of Imperturbatia may cluster with the Diapheridae when included in a molecular analysis. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160, 1–16.

Extensive series of Amphidromus Albers, 1850 were collected from low-altitude areas (30-500 m above sea level) in Thailand, Laos, Malaysia, Singapore and Indonesia between 1993 and 2004. Data on shell colour, genital and spermatophore morphology, and radular structure are presented. Five species of Amphidromus (Amphidromus) are reviewed, of which four occur in Thailand. Intraspecific variation between populations of Amphidromus (Amphidromus) atricallosus (Gould, 1843) is considered; three subspecies are accepted and a new subspecies described. Subspecies of A. (A.) inversus (Muller, 1774) and A. (A.) schomburgki (Pfeiffer, 1861) are reconsidered, and a new subspecies of the latter is described. A dichotomous key to the species and subspecies of Amphidromus (Amphidromus) in Thailand is provided.