Coriocella sp. 1 superficially resembles an opisthobranch mollusc, it is in fact classified into an entirely different group of molluscs, the Prosobranchia. The conventional schema of mollusc classification is to divide the Class Gastropoda into the following three Subclasses:
The following introduction to the Genus Coriocella is taken from Wikipedia:
Coriocella is a genus of small slug-like sea snails, marine gastropod molluscs in the family Velutinidae.
The ear-shaped shell is extremely thin, even membranous in part and concealed in the mantle. It has a small spiral turn at the apex. The aperture is very large. The shell lacks a columella.
The soft body is elliptical and much depressed. The borders of the mantle are very thin, notched in front and spreading out widely. The oval foot is very small. The head is scarcely distinct. The two short and rather thick tentacles are contractile and concealed under the shield. The eyes are situated at the base of the tentacles.
Species within the genus Coriocella include:
- Coriocella fella Er. Marcus & Ev. Marcus, 1970
- Coriocella herberti Drivas & Jay, 1990
- Coriocella hibyae Wellens, 1991
- Coriocella jayi Wellens, 1995
- Coriocella nigra Blainville, 1824 - type species of the genus Coriocella
- Coriocella safagae Wellens, 1999
- Coriocella tongana (Quoy & Gaimard, 1832)
I've added a second page with a "foot view" of the same featured animal; this image shows a bit of the lower head detail as well as the crawling surface of the foot.
Atsushi Ono (1999) has an apparent identical animal (80mm) which was photographed in the Kerama Islands (located 30 ~ 40 kilometers west of the Okinawa Capitol, Naha) as depicted in his book on page ten.
I've recorded two separate species of Coriocella on Okinawa's main island: