Rostanga australis from South Australia

June 25, 2002
From: John Chuk

Dear Bill,
Here are images of Rostanga australis and its egg ribbon found at Rapid Bay Jetty, South Australia. The species was common at the site and was always found on a dark blue sponge, often many specimens on the one sponge. The feeding scars were obvious as feeding exposed the pale orange to pink inner tissue of the sponge. Several sponges were found to be hollowed right out with the nudibranchs found on the inner surface. The first image is of such a specimen, which is very well camouflaged against the sponge. The shot was taken on 31 January 2002 at a depth of 5m and the specimen measured 30mm in length. I had to search to find it. The tell tale was the nearby egg ribbon which is shown in the lower left image. This ribbon measured 20mm in diameter.

Many egg ribbons were found and all were very similar in shape and size. They typically consisted of one and a half to two whorls of a flattened ribbon with a ragged crenulated margin. The colour varied from pinkish-orange to pale yellow.

The lower right image is of a specimen photographed on 1 February 2002 in situ on a sponge with many egg ribbons nearby. This specimen measured 16mm in length and was found at a depth of 6m.

Best wishes,
John.

jchuk@giant.net.au

Chuk, J., 2002 (Jun 25) Rostanga australis from South Australia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/7330

Thanks John,
This and your message of this species from Victoria are very useful additions to our knowledge of the species - effectively doubled our knowledge of the species. It appears that the blue sponge your animals were feeding on is a different growth form of the same animal I have illustrated from Yorke Peninsula where it grew as a series of flask-like structures. I wonder if there is some symbiotic algae or bacteria which is giving the sponge a blue layer in South Australia?
Cheers,
Bill Rudman

Rudman, W.B., 2002 (Jun 25). Comment on Rostanga australis from South Australia by John Chuk. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/7330

Factsheet

Rostanga australis

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