Rostanga risbeci? from Japan.

January 18, 2002
From: Jun Imamoto

Dear Bill.
I took these pictures of a sea slug which looks like Rostanga in a tide pool. Most Rostanga species which I know of are mainly orange. Therefore, I haven't been able to identify this sea slug.

I had advice that it looked like Rostanga risbeci from Mr. Hideyuki Takasu (Nudibranchs of Hachijo Island). Is it the same as the Rostanga risbeci which you commented on to Ms. Rie Nakano?

[Photograph data]
Date: 13 Jan 2002
Place: Shimoda, Izu Peninsula, Sagami Bay, Japan
Depth: 0.3m (Intertidal)
Size: about 12mm
Water temperature: 15C degrees.

Best Regards,
Jun Imamoto

Imamoto, J., 2002 (Jan 18) Rostanga risbeci? from Japan.. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jun,
It is difficult to be sure externally between species of Rostanga and Jorunna, but the shape of the gills - short and numerous, make me pretty certain that this is a species of Rostanga. And from its colour I would say that it fits Dr Baba's description of Rostanga risbeci very well. Dr Baba said it had been found feeding on a black sponge so perhaps next time you are at Shimoda could could see if you can find a black sponge. If you are lucky you might find an animal laying its egg ribbon on the sponge because in my experience species of Rostanga almost always lay their egg ribbons either on their food sponge or very close by.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Jan 18). Comment on Rostanga risbeci? from Japan. by Jun Imamoto. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Rostanga risbeci

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