Opisthobranch of the Week Data
Berthelinia schlumbergeri 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. Gosliner (1987) considers South African specimens of Berthelinia to be B. schlumbergeri, as this is the oldest species name for the group.
Berthelinia schlumbergeri is considered to be very rare on Okinawa as I have collected only the above single individual. I'd been watching for these unusual little animals for several years here and I had been unsuccessful, until the 16th of July, 1991, when I found three or four individuals on a relatively small colony of the green alga, Caulerpa racemosa. When I found the animals I didn't have my camera so I collected only a single specimen, to be photographed later at home (and unfortunately, a poor photo at that); the others were left intact as found, with the idea of returning with a camera the following day. As is the way of the "Great Okinawa Typhoon Gods", a storm moved in later in the day we went into a fairly good blow, and due to the rough waters I couldn't return to the divesite for a week; when I did get back with the camera gear I found the storm had totally erased the Caulerpa colony. No doubt, there's something here about the proverbial "A bird in the hand . . . ." I've continued to watch for additional animals in every reasonably encountered Caulerpa colony that I find, but I'm still without success at the present time.