Molecular Phylogenetic Analysis of Caridina weberi Species Group around Japan, with the First Record of Caridina tupaia de Mazancourt, Marquet & Keith, 2019 (Crustacea: Decapoda: Atyidae) from Japan

Recently, numerous new species of Caridina weberi species group were described from around Polynesia. This study reports the molecular phylogenetic data of the Japanese specimens belonging to C. weberi species group based on the mitochondrial 16S rRNA and cytochrome c oxidase subunit I gene. The results suggested that C. laoagensis Blanco, 1939, C. macrodentata Cai & Shokita, 2006, C. multidentata Stimpson, 1860, C. prashadi Tiwari & Pillai, 1971 and C. tupaia de Mazancourt, Marquet & Keith, 2019 are distributed in Japan. This is the first record of C. tupaia on Ishigaki-jima Island, Ryukyu Archipelago, southern Japan and the northernmost record of this shrimp. Attempted to find C. okinawa, belonging to C. weberi species group, for the first time in about 50 years, but there were no Atyid shrimps in its type locality. Based on the data of mitochondrial DNA fragments, we suggest that if the divergence estimate in C. weberi species group exceed 3% for 16S rRNA, it may be an interspecific variation. We also reveal the existence of two unnamed species which had been identified as C. macrodentata and C. multidentata. Caridina multidentata is known to be distributed in Japan (type locality), Taiwan, Fiji and Madagascar, however East Asian and Malagasy samples were shown to be distinct species, their divergence estimates were more than 10% for 16S rRNA. We also provide the key to the Japanese species of C. weberi species group.