Three new species of the karst-associated snorkel snail genus Rhiostoma (Caenogastropoda, Cyclophoridae) from Thailand revealed by integrative taxonomy

Integrating morphological and molecular datasets provides a robust framework for validating hidden biodiversity and describing novel taxa. In this study, three new species of the operculate land snail genus Rhiostoma are described from the isolated limestone karst ecosystems of northern and northeastern Thailand: Rhiostoma phuphamanense Prasankok & Pimvichai, sp. nov ., R. erawanense Prasankok & Pimvichai, sp. nov ., and R. lampangense Prasankok & Pimvichai, sp. nov . These novel clades are readily distinguished from all known congeners by discrete combinations of shell morphology (size, shape, and whorl counts). Multi-locus phylogenetic analyses (COI and 16S rRNA) paired with multi-approach species delimitation consistently supported the monophyly and distinct evolutionary clades of these three species, separating them from closely related sister taxa. Genetic divergence data further validated these boundaries, with the minimum uncorrected pairwise p-distance separating the three new species from other Rhiostoma clades exceeding 9.4% for the COI gene. Notably, R. erawanense sp. nov . exhibits extreme narrow-range endemism, currently restricted entirely to the microhabitats surrounding Tham Erawan (Erawan cave) in Phrae Province. Ultimately, the discovery of these three highly localized species significantly advances our understanding of Southeast Asian malacofaunal richness and underscores the urgent need for targeted habitat conservation within Thailand’s rapidly degrading regional karst landscapes.