Opisthobranch of the Week Data
Diaphorodoris mitsuii is considered to be very rare in Okinawan waters; I've not personally seen nor collected any specimens of this attractive little onchidoridid and it is currently unknown from Okinawa's main Island, but two animals have been collected and photographed by Atsushi Ono in the Kerama Islands. * The close proximity of the main island of Okinawa to the Kerama Islands, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on Okinawa's main island. The above featured animal is one which was photographed in the waters of Zamami Island by Atsushi Ono during August of 2005, in 2m of water amid branches of dead Acropora coral. Atsushi's photograph is used here with his kind permission and he considers the species to be very rare in the Kerama Islands, having seen only two individuals there (pers. comm.).
Baba described Diaphorodoris mitsuii (as Lamellidoris mitsuii) from a single specimen, approximately 5mm in length, dredged from Susaki, Izu. The following original description of the species is from Baba (1938):
Length of animal about 5 mm. Body elongate-elliptical, bluntly rounded at both ends. Back covered sparsely with small conical tubercles. Oral tentacles broad lobiform, with a slit-like mouth between them. Rhinophore-sheath with smooth margin. Branchial plumes 6, small, simply pinnate, completely retractile within a cavity with smooth margin. Foot produced behind in a fairly long tail, the anterior end abruptly rounded and simply labiate. Integument with spicules.
General body-colour yellow, margin of mantle with orange-yellow line fading out to yellow to the edge.
In addition, Rudman & Darvell (1990) point out a distinctive feature of the species is the distinct mid-dorsal ridge on the posterior end of the foot which, is apparent in Atsushi's photograph above.
Apparently Diaphorodoris mitsuii has a wide distribution; there are photos of the species recorded in the Sea Slug Forum (Rudman, 2001) from Hong Kong, Japan, and South Korea. The Forum features images of both yellow and white-bodied animals.
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.