DESCRIPTION AND FEMALE GENITAL STRUCTURES OF A NEW SPECIES OF THE DEMERSAL CALANOID COPEPOD RIDGEWAYIA FROM SOUTHERN JAPAN

A new species of the demersal calanoid copepod Ridgewayia, R. boxshall i n.sp., is described from southern Japan. This is the first record of the genus in Japan. It is distinguishable from other congeners by the antennule and leg 5 of both sexes. In order to identify evolutionary trends, detailed observations were also carried out on the female geni tal structures using light and scanning electron microscopy for compar ison with other calanoids. Their organization is characterized by two egg-laying ducts opening through paired gonopores into a small cavity, the genital atrium, covered by a genital operculum and opening to the outside through a distal atrial slit. No seminal receptacle is presen t. The unique morphological features and in situ feeding habit of Ridg ewayia are also noted.