Caridina sirindhornae sp. nov., A New Landlocked Atyid Species (Decapoda: Atyidae) from the Middle Mekong Basin, Thailand

A new species of landlocked and geographically restricted freshwater shrimp, Caridina sirindhornae sp. nov., is described from tributaries of the Mekong River in northeastern Thailand. The new species is morphologically similar to C. sumatrensis and C. maeklongensis by sharing characteristics such as a short antennular peduncle, the presence of epipods on the first four pereiopods, similar appendix interna on the male first pleopod, and a prominent subtriangular preanal carina without a spine. However, they can be distinguished by characteristics of the rostrum and egg size. Phylogenetic analyses based on partial sequences of the mitochondrial 16S rRNA and cytochrome oxidase subunit I (COI) genes (540 bp and 1,242 bp, respectively) robustly support the distinctiveness of C. sirindhornae sp. nov. Additionally, the findings show that the new species shares a sister relationship with C. lanceifrons, with a significant 16S rRNA p-distance of 6.74%, remarkably exceeding established species delimitation thresholds within the genus Caridina. This discovery represents the second landlocked Caridina species endemic to the Middle Mekong Basin in Thailand.