Joy ride or dinner?

March 28, 2008
From: Gary Cobb

Concerning message #21011:

Hi Bill and everyone!
Well, while you are on the subject of hitch hikers ... here is Glossodoris atromarginata with Gymnodoris sp.  My opinion is that the Gymnodoris is trying to get to its meaty heart and eat it. The Glossodoris seems to be in a position that seems to me to be in pain ... what do you thiink??
By the way, I did not see the Gymnodoris while in the water, only after reviewing the photos did I notice this happening!

Locality: Wait-a-while, Mooloolaba, Sunshine Coast, 14 m, Queensland, Australia, Pacific Ocean, 11 October 2003, Subtidal. Length: 10 mm. Photographer: Gary Cobb.

Gary Cobb

Cobb, G.C., 2008 (Mar 28) Joy ride or dinner?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Gary,

Thanks for your interesting photo. If I had a penny for every time someone sees something interesting in a photo for the first time I would be a rich man!

Your photo has an uncanny resemblance to Heidi Hösel's photo, which you refer to [#21011], of a Gymnodoris on Pectenodoris. The Gymnodoris in your photo is the one I have labelled Gymnodoris sp. 5. Concerning your theory of it eating the 'meaty' heart of the Glossodoris, I am afraid the heart of these animals is quite fragile. It essentially consists of a couple of layers of muscle fibres rather than a big block of muscle. I guess that as the blood is very thin and watery not a great effort is needed pump it around. I suspect if the Gymnodoris is eating, it is eating part of the body wall. Another possibility is that the Gymnodoris has just taken on an animal which is too big for it. I guess if they have an inbuilt instinct to bite or grab a potential prey item they can make mistakes.

If anyone has similar observations they would be very welcome. It is an interesting addition to the nudibranch feeding page.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Mar 28). Comment on Joy ride or dinner? by Gary Cobb. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Gymnodoris sp. 5.

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