Gymnodoris arnoldi from Victoria, Australia

March 21, 2001
From: John Chuk

Dear Bill,
Here is a picture of a nudibranch that I took on a night dive at Portsea Pier, Victoria, Australia on 19/12/2000. The specimen was one of two found in close proximity on the bottom at a depth of 4.5m. It is 13mm in length. I suspect that it is Gymnodoris arnoldi.

The reason for sending this picture is that this animal looks very similar to the specimen found at the same site and listed in the Forum as Polycera? sp.5. What do you think?

Best Wishes.

Chuk, J., 2001 (Mar 21) Gymnodoris arnoldi from Victoria, Australia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear John,
I think you are right on both counts. However, what we should call this animal is not so clear. Bob Burn described it as Nembrotha arnoldi and later placed it in the genus Gymnodoris [see top of page for references]. However I know of no anatomical information on this species. Burn's mention of a spiculate skin make it unlikely that this species belongs in either of these genera. I wouldn't mind some specimens if you find it again.
Best wishes,
Bill Rudman


Nembrotha arnoldi