First description of the female and morphological variation of Achalinushunanensis Ma, Shi, Xiang, Shu & Jiang, 2023 (Serpentes, Xenodermidae), with range extension of this species and A.yunkaiensis Wang, Li & Wang, 2019.

Background: The odd-scaled snake genus Achalinus, which is widely distributed in northern Vietnam, China and Japan, is a poorly-known group of snakes. Numerous species within this genus have been described based on few specimens or only a single type specimen. Achalinushunanensis Ma, Shi, Xiang, Shu & Jiang, 2023 was described based on only two male specimens from Huaihua City and Changsha City, Hunan Province, China. To date, this species has only been recorded in Hunan Province and the information on females is not available. During our herpetological surveys in 2024, two Achalinus specimens were collected from Guizhou Province, China. We compared morphology and mitochondrial DNA sequence data of these two specimens with all the species of the genus Achalinus. Both datasets strongly supported classification of the adult female specimen from Dushan County to A.hunanensis and the adult male specimen from Xifeng County to A.yunkaiensis.

New information: In this study, we describe the first female specimen of A.hunanensis in detail and provide revised diagnoses of this species based on newly-collected and examined specimens and update the distribution of A.hunanensis and A.yunkaiensis.