A new species of the genus Pleuroxus Baird (Cladocera: Anomopoda: Chydoridae) from Jeju Island, South Korea.

A new species of the genus Pleuroxus Baird (Cladocera: Anomopoda: Chydoridae) is described from Jeju Island, South Korea. P. jejuensis sp. nov. is the closest relative of the aduncus-like species from southern hemisphere instead of P. aduncus s. str. It shares with P. wittsteini Studer, 1878 in: (1) brown colour; (2) absence of denticles on postero-ventral portion of valve; (3) unusually short postpore distance; (4) grouped postanal teeth. P. jejuensis sp. nov. differs from P. wittsteini in: (1) smaller postpore distance; (2) submarginal setules on inner side of the posterior valve margin; (3) prominent postero-dorsal angle of the postabdomen; (4) only two postanal teeth in each group; (5) longer proximalmost basal spine of the postabdominal claw; (6) very short accessory seta on limb I. The wittsteini-like chydorines seem to be remnants of an old, pan-continental species group.