Twelve new species of the streptaxid snail genus Discartemon Pfeiffer, 1856 are described from southern Thailand and western Malaysia, D. afthonodontia sp. n., D. circulus sp. n., D. deprima sp. n., D. discadentus sp. n., D. discamaximus sp. n., D. expandus sp. n., D. flavacandida sp. n., D. kotanensis sp. n., and D. megalostraka sp. n. from southern Thailand, as well as D. conicus sp. n., D. epipedis sp. n. and D. triancus sp. n. from western Malaysia. All 15 previously described species are revised and commented upon based on examined material. Streptaxis paradiscus Möllendorff, 1900 is considered a junior subjective synonym of the type species D. discus (Pfeiffer, 1853). Details of the genital anatomy of twelve species, and the radula and pallial system, are provided for the first time. An identification key is provided.
A total of 30 specimens belonging to five species, namely; Cryptozona siamensis, Sarika resplendens and Sarika sp. from the family Ariophantidae as well as Quantula striata and Quantula sp. from the family Dyakiidae were collected from the Langkawi Island in Northern Peninsular Malaysia. All specimens were identified through comparisons of shell morphology and amplification of a 500 bp segment of the 16S rRNA mtDNA gene. To assess phylogenetic insights, the sequences were aligned using ClustalW and phylogenetic trees were constructed. The analyses showed two major lineages in both Maximum Parsimony and Neighbour Joining phylogenetic trees. Each putative taxonomic group formed a monophyletic cluster. Our study revealed low species and intraspecies genetic diversities based on the 16S rRNA gene sequences. Thus, this study has provided an insight of land snail diversity in populations of an island highly influenced by anthropogenic activities through complementary use of shell morphological and molecular data.