A new species in the Pareas hamptoni group (Squamata, Pareidae) from southeastern Laos

The slug-eating snakes of the Pareas hamptoni species group consist of approximately 15 species distributed across mainland Southeast Asia into northeastern India and southern China. A single specimen collected from the Dakchung Plateau in Xekong Province of southeastern Laos is shown to be molecularly and morphologically distinct from all related species in the P. hamptoni species group and is described as a new species. Pareas capitulatus sp. nov. is a smooth-scaled species having a distinctively narrow head and pattern on the nuchal region that was recovered as the sister taxon to approximately half of the members of the P. hamptoni species group. The inclusion of additional samples of P. geminatus from northern Laos demonstrated the non-monophyly of that taxon with respect to the morphologically similar P. xuelinensis and P. yunnanensis, all of which have type localities in Yunnan Province of southern China. To reconcile this taxonomic problem, P. geminatus and P. xuelinensis are treated as junior synonyms of P. yunnanensis. With these revisions, three species in the P. hamptoni species group are recognized from Laos: P. capitulatus sp. nov., P. formosensis, and P. yunnanensis. Further field surveys on the Dakchung Plateau and vicinity are needed to determine the geographic distribution and morphological variation in P. capitulatus sp. nov.