A taxonomic review of the freshwater shrimp genus Caridina H. Milne Edwards, 1837 (Decapoda, Atyidae) from southern Thailand, with descriptions of five new species

A comprehensive taxonomic review of the genus Caridina in southern Thailand is presented, integrating extensive field surveys with comprehensive morphological and molecular analyses to document the species diversity. Phylogenetic tree reconstructed from partial sequences of two mitochondrial genes (16S rRNA and COI) indicated 18 distinct lineages, recognized as species in our study, belonging to six species groups, from southern Thailand. Five of these are new to science and are described as C. kuehnei sp. nov ., C. nangroma sp. nov ., C. srivijaya sp. nov ., C. takkola sp. nov ., and C. tambralinga sp. nov . Including historical records, there are 21 species of Caridina found in southern Thailand of which almost half are endemic to the region. Updated distribution maps and a key to all known species in the region are also provided. Our findings highlight that while morphological identification is challenging due to significant intraspecific variation and interspecific similarity, molecular data is essential for helping taxonomists to delineate species boundaries.