Abstract
BACKGROUND: Calamaria andersoni Yang & Zheng, 2018, was originally described from a single adult male collected in Dehong Prefecture, Yunnan Province, China. Until now, no female specimens had been reported, limiting understanding of sexual dimorphism and diagnostic variation. Based on newly collected material from Mangshi City and Lianghe County, we identified five males and one female as C. andersoni through morphological comparisons and mitochondrial cytochrome b gene analysis. NEW INFORMATION: We provide the first morphological description of the female and revise the species diagnosis based on both sexes. The female is distinguishable by a higher number of ventrals and fewer subcaudals. Genetic data confirmed all specimens as belonging to a well-supported clade of C. andersoni, which is 9.8-10.1% divergent from C. yunnanensis. The known distribution of the species is extended to lower elevations (1,185-1,315 m a.s.l.) within tropical evergreen forests of Dehong. Given its relatively broad elevational range and occurrence in mature forests but no apparent population threats, we propose its conservation status as Least Concern (LC) under IUCN criteria. These findings provide new insight into sexual dimorphism, distribution, and species-level boundaries in Calamaria, emphasising the importance of continued surveys in underexplored montane regions of Yunnan and adjacent northern Myanmar.