Acanthodoris rhodoceras from California

October 16, 2003
From: Marina Tidwell

Hi Bill,
My son and I found this little guy in a shallow tidepool close to shore at Leo Carrillo State Beach in Malibu, California yesterday (October 13, 2003). It rolled into a ball when my son picked it up (the picture on the right) and then relaxed and turned right side up. We placed it on the rock to photograph it, but it was just lying on the sand of the pool when first found.

It looks like Archidoris montereyensis except its skin was smooth, it has black or deep green dots instead of rings, and a dark green line (it looks black in the picture) around the circumference of its body.

Any help you can give us would be greatly appreciated.
Marina Tidwell

Tidwell, M., 2003 (Oct 16) Acanthodoris rhodoceras from California. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Marina,
I am pretty sure your animal is Acanthodoris rhodoceras. The smooth body and submarginal blackish line around the edge are good clues. Also the blackish dots you describe look to me to be the tips of collapsed papillae. If you look at the species Fact Sheet you will see this species has pointed black-tipped papillae all over the back. These papillae collapse when the animal is taken out of water as you did to photograph it.

I don't think we know very much about this species apart from Goddard's (1990) report that it feeds on a bryozoan of the genus Alcyonidium sp. I presume he is talking about a flattened smooth sponge-like bryozoan, rather than one of the colonies which are often described as 'lace-corals
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Oct 16). Comment on Acanthodoris rhodoceras from California by Marina Tidwell. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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