OKINAWAN
OPISTHOBRANCH OF THE WEEK

Thorunna australis (Risbec, 1928) 18mm

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        Thorunna australis is considered to be rare in the waters of Okinawa's main island. I've collected three individuals. The above featured animal was found crawling near the base of a vertical pier piling, which was covered with numerous invertebrates (cnidarians, bryozoans, pelecypods, and poriferans) during a daytime SCUBA excursion.

        Thorunna australis is superficially similar in appearance to another Okinawan chromodorid, Hypselodoris maculosa. Bill Rudman (1998) points out:

"This species has some similarities to some colour forms of Hypselodoris maculosa but whereas that species has multiple longitudinal white lines Thorunna australis has only one on either side of the mantle. Both species have reddish bands on the rhinophores, always one in T. australis but up to three in H. maculosa."
The color pattern of the above featured animal fits the description in Rudman's (1986) paper as follows:
"On each side of the mantle from along side the rhinophores there is a thin opaque white line which runs back to just behind the gill pocket, and on the outside of each of these lines are purple-red spots forming a submarginal row...."
Here are images of two additional specimens of T. australis, illustrating some of the color variation seen within the species.

        Thorunna australis is one of six described species of Thorunna known from Okinawan waters. The six species are:

Literature Cited:


Page Date: 6 Dec '99
Page Modification Date: 05 Nov '07
Digitally manipulated photo
Copyright © 2007 Robert F. Bolland