Four new species of genus Acmella W.T. Blanford, 1869 (Gastropoda, Assimineidae) from Southern Thailand

This study explores the diversity of microsnails inhabiting limestone caves in Southern Thailand. It describes four new species of the genus <i>Acmella</i> W.T. Blanford, 1869 (Gastropoda, Assimineidae): <i>Acmella krueangensis</i> <b>sp. nov.</b> from Ranong Province, <i>A. thamsingensis</i> <b>sp. nov.</b> and <i>A. changphueakensis</i> <b>sp. nov.</b> from Chumphon Province, and <i>A. kanchanaditensis</i> <b>sp. nov.</b> from Surat Thani Province. These species are distinguished by shell morphology, particularly the number of striae on the last whorl and the protoconch sculpture. Phylogenetic analyses based on mitochondrial cytochrome c oxidase subunit I (<i>COI</i>) gene sequences further support their distinctiveness and clarify their taxonomic placement. The results enhance the understanding of <i>Acmella</i> diversity in Thailand and shed light on biogeographical patterns found in this genus and the adaptations needed to survive under the conditions of cave systems.