Costasiella usagiIchikawa, 1993
I canít tell you how much I love seeing all the fabulous photos of sacoglossids found In Rie Nakanoís new book Opisthobranchs of the Islands of Japan and Atsushi Onoís companion book Opisthobranchs of Ryukyu Islands . Here is Costasiella usagi described by Ichikawa in 1993. It can be found on page 68 of Ono-sonís book. This strikingly colored species is one of over three dozen sacoglossid nudibranchs presented in the two books.
Looking very much like an aeolid nudibranch, members of the genus Costasiella have rolled rhinophores. Although quite variable in color, as indicated on Bill Rudmanís Sea Slug Forum , Ichikawa's description the color is described as: "The head and tail are not pigmented, and the rhinophores are black. The median cerata are grey, while the outer ones are black. All the cerata possess a white end and a black tip. Moreover, all the cerata bear longitudinal striations reaching from the base of each ceras to the white apical portion. ... The ventral side of the foot is white. .... Smaller specimens have the median cerata colored green, instead of grey."
The geographic range of this species seems to be throughout the tropical western pacific, including northern Australia, Guam and Japan. Specimens measure about 3-7 mm in length and are reported to feed on the algal species, Avrainvilla.Costasiella usagi was also presented a couple of weeks ago on Bob Bolland's Okinawa Slug Site as the slug of the week!
Between this web site, Bob's Site, and Bill Rudmanís Sea Slug Forum and the many new high quality books we are seeing come out today, we are all very lucky.
Ichikawa, M. (1993) Saccoglossa Opisthobranchia) from the Ryukyu Islands. Publications of the Seto Marine Biological Laboratory, 36: 119-139.
I feel so strongly about the Ono-san's dedication to the study of Opisthobranchs that he is going to receive my unqualified recommendation for anyone planning a branching trip to Okinawa. His operation is first class and can be totally focused on branching if you bring enough people.
David W. Behrens
Pacific Coast Nudibranchs
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