Lamellaria sp. 1 (23mm)
ANIMAL OF THE WEEK
Lamellaria sp. 1 (foot view of the above 23mm individual)
Opisthobranch-like Animal of the Week Data
Frequency on Okinawa:
- Class: Gastropoda
- Subclass: Prosobranchia
- Order: Mesogastropoda (Vetigastropoda)
- Family: Lamellariidae (Velutinidae)
- Very rare, only a single(?) individual collected
[data for the twelve collected Lamellaria specimens in brackets above; some are perhaps the same species]
- Individual Collection No: RFB #3803-A
- Location: Seragaki, Okinawa (26o 30.4'N, 127o 52.6'E) [all twelve Lamellaria specimens from two locales: Horseshoe Cliffs & Seragaki]
- Date: 22 June, 2000 [Mar '89, May '89, Jul '89(2), Sep '89, Nov '89, Aug '91, Feb '92, May '95, Jul '95, Jun '00, Jun '01]
- Depth: 10ft (3m) [5ft, 5ft, 5ft, 5ft, 5ft, 10ft, 10ft, 30ft, 160ft, 180ft 205ft, 235ft]
- Water temperature at collection depth: 81oF (27oC)
- Size: TL 23mm [3mm, 4mm, 12mm, 12mm, 14mm, 15mm, 16mm, 18mm, 20mm, 20mm, 21mm, 23mm]
- Specimen deposited: RFB Personal Research Collection
- Photo Data: Originally image taken with digital film
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:
- 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;
- 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.
The above featured Lamellaria sp. 1, is considered to be very rare on Okinawa's main island in as much as this is the only collected specimen. However, it could well be that several of the twelve collected specimens are of the same species. This animal was found during a mid-morning scuba excursion during a relatively high spring tide. It was located beneath a slab of coral rubble in a mixed sand and coral rubble environment. My experience in finding these small prosobranchs is that they are normally found on the surface of small compound tunicates; Lamellaria so closely resembles the host tunicate upon which it lives and feeds that only a careful close inspection allows it to be detected. This was the case with the above featured specimen.
Dave Behrens (1980) lists some of the nomenclatural problems associated with members of the family in the waters of the North Eastern Pacific. Bill Rudman (1998) discusses on the Sea Slug Forum some of the taxonomic problems associated with this group, notably the problem involving many of the species being named from dead shells, which are often very similar in shape. Until someone undertakes some detailed research on the family there will continue to be identification problems. There are lots of good photographs of living animals but no serious attempt has been made as yet to match the living animals with the dead shells.
I've added a page of thumbnail images which link to an additional page illustrating all twelve of the Okinawan specimens.
In addition to the above animal, I've also have links to the following animals which are similar in appearance to opisthobranch molluscs:
- Behrens, D.W. 1980. The Lamellariidae of the North Eastern Pacific. Veliger 22(4):323-339.
- Rudman, W.B., 1998 (October 28). What are lamellariids & velutinids? [In] Sea Slug Forum. http://www.seaslugforum.net/lamellar.htm
Page Date: 11 Aug '03
Page Modification Date: 01 Oct '13
Digitally manipulated photo
Copyright © 2013 Robert F. Bolland