Taxonomic and distributional revision of Pareas boulengeri (Reptilia, Squamata, Pareidae), including two new species from eastern and central China

The Boulenger’s slug snake (Pareas boulengeri Angel, 1920) has previously been documented as relatively widely distributed across the eastern, southern, and southwestern regions of China. In the present study, integrated morphological comparisons and molecular phylogenetic analyses were undertaken to reevaluate the taxonomic status of P. boulengeri and to describe two new species: Pareas dabieshanensis sp. nov. and Pareas orientalis sp. nov.

Phylogenetic reconstruction based on CYTB gene sequences indicated that populations previously identified as P. boulengeri comprise three distinct lineages: true P. boulengeri, P. dabieshanensis sp. nov., and P. orientalis sp. nov. The two new species exhibit significant genetic divergence from their congeners, with uncorrected pairwise distances of 4.1–4.5 %, consistent with interspecific divergence within the genus. Morphologically, P. dabieshanensis sp. nov. is distinguished by the presence of two subocular scales, the absence of preocular scales, and higher ventral (184–187) and subcaudal (68–74) counts.

P. orientalis sp. nov. is characterized by a single preocular scale and fused subocular and postocular scales. The revised distributions restrict P. boulengeri to southwestern China, while the new species are confined to the Dabie Mountains (Anhui, Hubei, Henan) and eastern China (southern Anhui, Jiangsu, Jiangxi, Zhejiang), respectively. The non-overlapping ranges of P. dabieshanensis sp. nov. and P. orientalis sp. nov., bisected by the Yangtze River, suggest that this major hydrological system acted as a biogeographic barrier driving speciation.

This study expands the genus Pareas to 33 recognized species (27 in China) and underscores the prevalence of cryptic diversity within morphologically conserved lineages.