Expanded morphological definition and molecular phylogenetic position of the Tam Dao mountain stream keelback Opisthotropis tamdaoensis (Squamata: Natricidae) from Vietnam

The description of Opisthotropis tamdaoensisZiegler, David & Vu, 2008, which was based on the male holotype only, is expanded herein on the basis of four newly collected specimens from the type locality of the species, including three adult females. Based on the enlarged sample size and thus extended range of morphological characters in O. tamdaoensis, not all characters mentioned in the original description as being distinctive between the latter species and O. lateralisBoulenger, 1903, a morphologically similar species, could withstand, such as number and arrangement of preocular, temporal and subocular scales, as well as total size. Presently, the number and arrangement of supralabials in concert with the dorsal colour pattern and the course of the dark lateral stripe still serve as good diagnostic characters to morphologically distinguish O. tamdaoensis from O. lateralis. Thus, on the basis of the new morphological and for the first time also molecular data, the validity of O. tamdaoensis as a distinct species is confirmed. The molecular analyses based on the mitochondrial cytochrome b gene revealed O. tamdaoensis to be distinct by about 6% genetic divergence from O. lateralis, with which it forms a sister relationship.