Opisthobranch of the Week Data
Polycera risbeci is considered to be rare in Okinawan waters; Atsushi Ono reports (per. com.) seeing over ten individuals, however, the species has not as yet been seen in the waters of Okinawa's main island. The above featured animal was found and photographed on mixed silty-sand and coral rubble by Atsushi in December of 1998 from the Sakubaru dive site off Aka Island, Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. Atsushi has kindly furnished the above image of this approximate 5mm sized animal and is used here with his permission.
The following description of the species is taken from Marshall & Willan (1999):
This is a very small dorid nudibranch that cannot retract the gills into a pocket beneath the mantle. The mantle is without a notal brim separating it from the foot and the tail is long and pointed. The mantle's surface is smooth except for indistinct pustules on the dorsum and sides. A series of nine papillae are present around the oral veil. The rhinophores are large and lamellate, and there are three gills.
The body is vivid greenish yellow with thin, interrupted, transverse brown lines. The papillae on the head are paler than those on the rest of the body. The rhinophores are pale brown with yellow flecks on the lamellae. The gills are pale yellow.
Polycera risbeci is distinctive in possessing brown transverse lines on the body.
The diet is unknown. Polycera risbeci lays a white spawn coil with only a few whorls.
The only other described Polycera species from Okinawan waters of which I'm aware are P. abei, P. fujitai, and P. risbeci, all from the Kerama Islands.