3 NEW SPECIES OF THE DEMERSAL CALANOID COPEPOD PLACOCALANUS (RIDGEWAYIIDAE) FROM OKINAWA, SOUTHERN JAPAN

Three new species of Placocalanus are described from sandy bottoms off Nagannu Island, Okinawa, southern Japan, at a depth of ca 50 m. This is the first record of the genus in the Indo-Pacific region. A number of differences in segmentation and setation in appendages are found be tween the Pacific and Atlantic species. In particular the Pacific spec ies have a reduced number of setae of the legs compared with their Atl antic congeners. Specialized characters of Placocalanus such as the la terally compressed prosome, expanded proximal plate of the antennule a nd markedly modified leg 1 are discussed from a functional point of vi ew. Cooccurrence of several species of a genus is common among demersa l calanoid copepods, and is briefly discussed.