Re-description of Trachischium nyalamense Guo, Liu, Jin, Shu, Wu & Che, 2024 (Serpentes, Natricidae), with notes on skull morphology and reproductive biology

Trachischium nyalamense Guo, Liu, Jin, Shu, Wu & Che, 2024 was recently described, based on a single adult male specimen collected from Zhangmu Town, Nyalam County, Xizang Autonomous Region, China. Due to the limited material available, important aspects of its biology and morphology, including sexual dimorphism, skull morphology and reproductive biology, remain poorly understood. In July 2025 and June 2026, three adult female specimens and one adult male specimen, respectively, were collected from the type locality of T. nyalamense . One of these females was found in association with a clutch of seven fertilised eggs in the field. Phylogenetic analyses, based on the mitochondrial 16S and Cyt b gene fragments, showed that the newly-collected specimens clustered with the holotype of T. nyalamense with high support and no genetic differentiation was detected amongst individuals ( p -distance = 0.0%). Further morphological examination revealed that the four newly-collected specimens generally agree with the diagnostic characters of T. nyalamense , differing only in minor features attributable to normal sexual dimorphism. Based on these four new specimens and three hatched juveniles, we provide a detailed re-description of T. nyalamense , including its skull morphology and report its reproductive biology.