Hidden diversity in China's Sky Islands: Three new freshwater snail species of Erhaiidae (Gastropoda, Truncatelloidea) from the Yunnan-Guizhou Plateau

Alpine freshwater ecosystems in southwestern China, particularly those exhibiting sky-island characteristics (geographically isolated high-elevation habitats surrounded by contrasting lowlands), represent critical yet understudied hotspots for aquatic biodiversity evolution. The minute gastropod genus Erhaia (<3 mm shell height) exemplifies this pattern, with species distributed across fragmented high-elevation streams from the Himalayas to eastern China.

Despite 20 described species, the group’s diversity is likely underestimated due to their small size, collection neglect, and the lack of recent records — including the type species, E. daliensis, which has not been recollected since its original description. During field surveys conducted in 2023–2024, we rediscovered E. daliensis at its type locality in Yunnan, Chinas, and identified three new species: E. xiaoboqiani H. Chen, Y. - M. He, H. - Q. Xiang & X. - P. Wu, sp. nov., Erhaia guizhouensis H. Chen, Y. - M. He, H. - Q. Xiang & X. - P. Wu, sp. nov., and Erhaia bailong H. Chen, Y. - M. He, H. - Q. Xiang & X. - P. Wu, sp. nov. from mountain streams in Yunnan and Guizhou.

Combining morphological and molecular evidence (mitochondrial COI, 16 S; nuclear 18 S, 28 S), we formally describe these taxa and discuss their biogeographic implications for understanding diversification in sky-island-like freshwater systems.