Descriptions of two Cypridopsinae (Ostracoda, Crustacea) species from the Nansei Islands, Japan, with the first records of non-marine ostracods from the Daito Islands.

A new species, Potamocypris kusuokai sp. nov., is described based on males and females collected from Kitadaitojima, the northern-most of the Daito Islands, part of the Nansei Island archipelago in southwestern Japan. In addition, four other non-marine ostracod species found during sampling of the Daito Islands are reported, and these, together with the new species, are the first non-marine ostracods to be recorded from these remote Pacific islands. Potamocypris sudzukii Okubo, 1992, described from female specimens collected from Okinawa and Kuroshima, also part of the Nansei Islands, is redescribed based on a paratype specimen. This species is transferred to the genus Siamopsis Savatenalinton, 2017, which previously was only known from Thailand, extending the known distribution of the genus eastwards by about 2500 km. Plesiocypridopsis arsenia (Tressler, 1937), from the Philippines, is also transferred to Siamopsis, based on its original description. An overview of the current state of knowledge of non-marine ostracods of the Nansei Islands is provided.