Opisthobranch of the Week Data
The following presentation is one featuring a member of one of the two holoplanktonic* orders of opisthobranch molluscs (Thecosomata and Gymnosomata) featured on these pages. The featured animal is Diacria trispinosa, which is a thecosome belonging to the family Cavoliniidae. Members of both orders are sometimes referred to as pteropods ("winged foot") and sea butterflies. The original foot of the animal has developed into a pair of "wings" (parapodia), which increase the animals' capacity of both buoyancy and locomotion.
The above featured animal is one which was collected from a "grunge"** sediment collection from Horseshoe Cliffs, but unfortunately without additional data. I've occasionally found shells of family members in such collections while on SCUBA in relatively deep waters here and a small series of these are shown on a second page. This second page also has an excellent image of D. trispinosa taken in the Keramas by Atsushi Ono and used here with his kind permission.
Tomohiko Kurihara has a great image of a living specimen of D trispinosa photographed in the ocean, taken at the Ipponmatsu dive site, Osezaki, Japan.
For additional information on this fascinating group of opisthobranchs see the following two Wikipedia sites concerning the Superfamily Cavolinioidea and a presentation involving both description, and a family and species list.
* Holoplanktonic: planktonic organisms living in open water, as opposed to the meroplankton which are found only "part time" in the plankton.
** "grunge": A term used to describe sediment collections. While on SCUBA, usually in relatively deep water, a chunk of coral or rock rubble is picked up by hand and a hand scoop of sediment is collected from beneath the rubble and transferred into a Zip-Loc bag and inspected later at home. The material is then washed and dried. Numerous micro-molluscs, et al, have been collected in past years in this manner and sent to the L.A. Co. Mus. Nat. Hist. The term grunge, as used in the current context, is not to be confused with the style of rock music that incorporates elements of punk rock and heavy metal, popularized in the early 1990s. (grin)