Opisthobranch of the Week Data
Julia exquisita belongs to a remarkable group of bivalved gastropods and their shells are well known from the fossil record. These little sacoglossan opisthobranchs were originally described as bivalves (pelecypods), based on fossil solitary shells, but in the late 1950's Kawaguti & Baba (1959) described the living animals. Some workers have divided the group into multiple genera, but many of the species apparently differ in only minor variations of shell morphology. Kathe Rose Jensen, who is currently working in Thailand, offers the following information concerning the genus Julia (pers. comm.):
The genus Julia is unfortunately so poorly known that it is almost impossible to say which of the species names in current circulation are valid and which are synonyms. The only species that seems to be discernible on external features alone is Julia zebra Kawaguti, 1981. Other species names used for Japanese specimens are Julia japonica Kuroda & Habe, 1951 and Julia mishimaensis Kawaguti & Yamasu, 1982. The oldest valid name for Indo-Pacific species of Julia is J. exquisita Gould, 1862, and until someone gets enough material from different locations in the region to perform a detailed analysis of anatomy and variation in shell morphology, I suggest that we use this name for the species with a uniformly green shell.
Julia exquisita is unknown from Okinawa Island as of mid-March, 2001, but the close proximity of Okinawa to the Kerama Islands suggests the possibility that it is also present here on Okinawa. The above featured, but uncollected animal, is one which was photographed in the waters of Zamami Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. This featured animal was photographed by Atsushi Ono during July of 2000 off of Furuzamami Beach in approximately 5m of depth. Atsushi's photograph is used here with his kind permission. It should be noted that Atsushi considers the species to be very rare in the Kerama Islands as he has seen only the above featured single individuals (per. comm.). Not a great deal is known of the feeding habits of J. exquisita, although Marshall & Willan (1999) report the animal feeds on fine, filamentous green algae.
There are photos of the valves of J. exquisita on Guido T. Poppe's Conchology site; Bill Rudman has a series of the valves of the species displayed on the Sea Slug Forum as well, nicely illustrating how variable the valve color may be.
The only species of this interesting group of sacoglossans which I've personally collected here on the main island of Okinawa is an animal which I'm currently calling Berthelinia schlumbergeri.