OKINAWAN OPISTHOBRANCH-LIKE
ANIMAL OF THE WEEK

Opisthobranch-like Animal of the Week Data

Taxonomy:

        Once again, as with several earlier presentations, I've decided to depart from the usual opisthobranch presentation with the above featured animal. Although it superficially resembles an opisthobranch, it in fact is 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:

        Scutus unguis is considered to be very common on Okinawa; numerous individuals have been seen here, primarily in the upper 30ft of water. They are commonly seen on the underside of coral rubble slabs as the rubble is overturned. Also, lone Scutus shells are a common sight in the intertidal zone, suggesting a fairly high mortality rate. Scutus species are not slugs but a marine snail with a white shield-like shell on its back. The shell is frequently covered by flaps of the mantle, but sometimes the mantle is withdrawn and exposes a portion of the shell. It belongs to the family Fissurellidae which includes the Slit-Limpets and Keyhole Limpets, named from the slit or "keyhole" opening in their limpet-shaped shell; these openings allow for the discharge of water from the mantle cavity. Scutus species have only a notched shell, as seen in the above image. The relatively large number of questions posted by home aquarists to Bill Rudman on the Sea Slug Forum (Rudman, 2000) supports how slug-like (opisthobranch-like) these animals are.

        In addition to the above prosobranch, I've also have links to the following animals which are similar in appearance to opisthobranch molluscs:

Literature Cited: