Costasiella kuroshimae

Photo Courtesy of Atsushi Ono
Costasiella kuroshimae Ichikawa, 1993

Atsushi Ono, author of Opisthobranchs of Kerama Islands , was kind enough to make available this beautiful Sacoglossid for the Slug Site. Costasiella kuroshimae was described in 1993 as being of typical aeolid body shape with a flat tapering cerata. Its white head has a unique color pattern. The pattern is made up of dark marks in the midline and a dark streak across the head just in front of the rhinophores. This species also has a dark grey-black streak on the dorsal midline behind the eyes. The rhinophores are white with black tips. The cerata are green with white tips, and are covered with iridescent specks. Some specimens have a yellow-orange ring on the cerata.

Unfortunately the description of Costasiella kuroshimae was brief and somewhat incomplete as pointed out in Bob Bolland's Opisthobranch of the Week , last week. This situation has complicated the taxonomy of the genus on a whole from this region and is responsible for some experts to set the genus aside as it is now a total mess. This results in species being referred to as Costasiella c.f. kuroshimae as seen on Bill Rudman's Sea Slug Forum . Sloppy science only make matters worse.

Only a few millimeters in length, Costasiella kuroshimae feeds on the green algae, Avrainvillea . This species is named after Kuro Island, in the Yaeyama Islands, of Japan where it was first found. The geographic range pieced together from Ichikawa's vague description suggest it likely also occurs throughout the Kerama Islands, Okinawa, as indicated by Atsushi Ono and Bob Bolland.

Dave Behrens
Danville, Calif
Mar. 2003

Webmaster, Atsushi Ono, and Jerry Allen
May 2002
Photo courtesy of Akiko Miyamoto

Atsushi Ono is the owner of a dive service on Zamami Island in the Keramas off Okinawa that caters mainly to Japanese Divers. Atsushi evidently relocated from a small town north of Tokyo some fifteen years ago to Zamami Island. He subseqeuntly started a diving service. In fact, the economy of Zamami Island seems to based entirely on diving! For those of you who don't speak Japanese that is not a problem communicating with Atusushi, his written english is very good! Atsushi has a passion that so many of us also share and that is the observation and study of sea slugs. Atsushi published a field guide "Opisthobranchs of Kerama Islands " a couple of years ago that excels in the macro photography of small Japanese slugs. His book is a must for any of those considering travel to that area of the world. We spent many an evening with Atsushi sharing pictures and experiences with branches. His enthusiasm is very intense, one can feel it in both talking and diving with him! Atsushi has been a regular contributor to the Okinawa Slug Site maintained by Bob Bolland.

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. With the impending conflict with Iraq, Japan would seen to be a safe habour in these troubled times.

You can drop Atsushi a note at

Taxonomic information courtesy of:

David W. Behrens

Author: Pacific Coast Nudibranchs
Co-Author Coral Reef Animals of the Indo Pacific
Proprietor of Sea Challengers Natural History Books !

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