Yixiong Cai
During a taxonomic revision on Caridina of East and Southeast Asia, a group of amphidromous and anchialine Caridina species, i.e., Caridina serratirostris, C. celebensis, C. rubella, C. troglodytes, C. magnovis, C. rintelenorum, and C. henriettae, widely distributed in the Indo-Pacific region has been found to exhibit distinct and unique morphological characters, e.g., rostra moderately long and straight, armed with many dorsal teeth, at least six of them on the carapace; telson terminating in a posteromedian projection; stylocerite long, reaching to or beyond the end of the basal segment of the antennular peduncle; and preanal carina with a spine, and with slender walking legs. Genetically, the group forms a monophyletic clade, either alone or together with the genus Marosina. The clade is well-separated from other species/species groups of Caridina. By taking a conservative taxonomic approach, the genus Marosina is thus redefined to accommodate members of the C. serratirostris species group. The revised genus Marosina can be separated from the typical Caridina species (represented by Caridina typus species group) by the structure of the endopod of the male first pleopod, which does not have an appendix interna, and the long stylocerite, which reaches to or beyond the end of the basal segment of the antennular peduncle, and the high number of postorbital teeth on the carapace. The paper provides a revised diagnosis of Marosina, with a key to all species assigned to it. Diagnosis, taxonomic remarks, habitat, and distribution information for all species are provided. The ecology, biogeography, and conservation of the genus are briefly discussed.