Coriocella sp. 1 (68mm)
ANIMAL OF THE WEEK
Opisthobranch-like Animal of the Week Data
Frequency on Okinawa:
- Class: Gastropoda
- Subclass: Prosobranchia
- Order: Mesogastropoda (Vetigastropoda)
- Family: Lamellariidae (Velutinidae)
[brackets indicate range for all Okinawa-collected specimens of the species]
- Individual Collection No: RFB #3306
- Location: Horseshoe Cliffs, Okinawa (26o 30.0'N, 127o 50.9'E) [only a single collected individual]
- Date: 11 September, 1994
- Depth: 180ft (55m)
- Water temperature at collection depth: 76oF (24oC)
- Size: TL 68mm [only a single collected individual]
- Specimen deposited: California Academy of Sciences
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:
- The opisthobranchs include the sea slugs and their relatives the sea hares, sea butterflies, and others. The bodies of most member of this group show evidence of detorsion. Shells may or may not be present; if present they may be reduced and/or internally located. Opisthobranchs usually lack a mantle cavity and operculum. Many species lack gills and respiration takes place through the skin, which may bear numerous projections and folds that increase the area for gas exchange. The head bears 1-2 pairs of tentacles. This diverse group of organisms is divided into around nine Orders. There is some disagreement about whether these form a monophyletic group.
- Prosobranchs are the largest subclass of gastropods. Most species are marine, but many freshwater species and a few terrestrial forms are also known. Prosobranchs have an operculum (lacking in pulmonates), and most have a spirally coiled shell. The head includes eyes that are located on tentacles. The mantle cavity is anteriorly directed and near the head. They are divided into three Orders, Archaeogastropoda, Mesogastropoda, and Neogastropoda.
- Pulmonates are the land snails and slugs (a few species are marine). A coiled shell is usually present, but it is lost in some groups. Some detorsion has occurred in many species. The Subclass derives its name from the fact that the mantle cavity forms lungs; these are filled with air as a result of contractions of the mantle floor. One or two pairs of tentacles are found on the head, depending on whether the snail or slug is terrestrial (two pairs) or aquatic (one). The nervous system is highly concentrated. Pulmonates are dioecious and hermaphroditic as are prosobranchs, but pulmonates develop directly (there is no larval form).
There is a fair amount of confusion concerning the family designation of this group of prosobranchs. I've opted to use the Family Lamellariidae which is composed of about six genera (Dave Behrens, pers. comm.), including, Coriocella, Lamellaria, Marsenina, Marseniopsis, and Mystinconchya.
Coriocella sp. 1 is considered to be very rare on Okinawa's main island as I have seen and collected only the above featured animal. This unusual animal was found during a mid-morning dive from beneath a large slab of coral rubble in an area of mixed sand and strewn coral rubble. 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) depicted in his book on page ten. 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.
I've recorded two separate species of Coriocella here on Okinawa's main island:
- Ono, Atsushi. 1999. Opisthobranchs of Kerama Islands, TBS-BRITANNICA & Co., Ltd., Japan. 184pp.
Page Date: 18 Nov '02
Page Modification Date: 25 Aug '03
Digitally manipulated photo
Copyright © 2003 Robert F. Bolland