First description of the female of Achalinus vanhoensis Ha et al., 2022 (Squamata, Xenodermidae), with a new distribution record from northern Vietnam

Achalinus vanhoensis Ha et al., 2022 was previously known only from the adult male holotype collected in Van Ho, Son La Province, northwestern Vietnam. The second known specimen and first known female of the species are reported from Cuc Phuong National Park, Ninh Binh Province, northern Vietnam. Morphologically, the female differs from the male holotype mainly in having a proportionally shorter tail (tail length/total length ratio 0.192 vs. 0.264), more ventrals (202 vs. 176), and fewer subcaudals (74 vs. 84). These differences may reflect sexual dimorphism in A. vanhoensis . However, as the species is currently known from only one specimen of each sex, additional specimens are required to determine whether these differences represent consistent sex-related variation or individual variation. Molecular phylogenetic analyses showed that the newly collected specimen clustered with the holotype with moderate support and exhibited an uncorrected COI p -distance from it of 3.8%, supporting its identification as A. vanhoensis . The new record extends the known range of the species approximately 112 km southeastward and lowers its documented elevational limit from 1,121 to 440 m a.s.l. An updated identification key to the nine species of Achalinus recorded from Vietnam is also provided, and it is provisionally recommended that A. vanhoensis be assessed as Data Deficient (DD) under the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee 2024).