Opisthobranch of the Week Data
Elysia yaeyamana is considered to be very rare in Okinawan waters. Both Atsushi Ono and myself have collected only a single individual as of the current date. The above featured animal is the one photographed by Atsushi in the Keramas * from Zamami Island and used here with his kind permission. I've added a second page with two images of the animal collected by RFB (from Horseshoe Cliffs, 15 July, 1992) from the waters of Okinawa's main island. I'm using Atsushi's above photo as it's considerably better than either of my own.
Baba (1936) described Elysia yaeyamana from the waters surrounding Ishigaki Island during 29 June, and 13 July, 1934. Baba mentions collecting "many specimens" from Ishigaki which is located approximately 460km Southwest of Okinawa's capital, Naha.
The following description of Elysia yaeyamana is taken from Baba (1936):
The body is smooth, slender, limaciform and 50-70 mm in length in the living state. The rhinophores are rolled and situated at the antero-lateral corners of the head. The neck is long and the sides of the body are expanded into two mantle lobes which are not very wide. The pericardium, when preserved, is constricted in the middle. The foot is of the full length and width of the body, widened at the antero-lateral sides and narrowed behind.
Nearly the whole surface of the body is of a green or brownish green colour; the outer and inner surfaces of the mantle lobes are covered with paler or whitish mottles. The upper portions of the rhinophores are yellow and the mantle borders are tinged with orange-yellow.
The radula has 13 teeth (exclusive of those in a basal heap) arranged in a single row and the formula is 13 x 0.1.0. The tooth is hamate with a large base and a pointed blade, and the latter bears minute serrulations at the antero-ventral margin.
The present species somewhat resembles Elysia viridis (Montagu) in the body-coloration and type of the radula, but is distinct because of (1) the rhinophores with yellow tips and (2) the mantle lobes elegantly margined with orange-yellow. It does not appear to correspond to any of the known species in the peculiar coloration or in the minutely serrulated teeth, and hence it is described here as a new species to which the name Elysia yaeyamana has been given.
In addition to the above featured Elysia yaeyamana, the following Elysia have been previously featured on these pages:
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.