Dermatobranchus ornatus - Feeding & mantle glands

April 8, 2008
From: Gaetan White

Dear Bill
I cannot imagine how I (and many adults and school kids whom i have introduced the Forum to, especially in remote asian localities) could thank you for your constant work, and the top educational level of info and exchanges.

Whilst searching for previously seen (twice the previous day) shovelnose ray accompanied by a juvenile (Rhinobatus (djiddensis, sp.) Sven Jakubith and myself grabbed a few pics of this sole Dermatobranchus ornatus. It seemed well intent on staying enravelled on the coral (what is it?) and totally stripping it of its surface and polyps. Originally I thought it was Maiazoon orsaki [flatworm], so did not bore you with that, but "Sea Slug Forum" curiosity made me contact Sven to see if he had better pics (definitely visible rhinopores). What intrigued me in the first place was the unusual orange border around its foot! In the middle photo one can clearly see some (chemical) cells around the underneath edge of the mantle. Please correct my layman's terminology.

Locality: Elephant head, 20 m., Thailand, Similan, 23 january 2007 sun rise, Large sandy slope between boulders. Length: 100 mm. Photographer: Gaetan WHITE and Sven JAKUBITH.

Thank you again,

White.G.A and Jakubith.S., 2008 (Apr 8) Dermatobranchus ornatus - Feeding & mantle glands. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

ear Gaetan,
I'm glad you find the Forum valuable. As your contribution illustrates, 'science' gets quite a lot of valuable new information from questions such as yours.

As you will see from earlier messages to the Forum, it seems pretty certain that D. ornatus feeds on gorgonian soft corals. Your photos and observations certainly add to that idea, as the 'coral' in your photos is a gorgonian. There is also quite a lot of evidence to show that soft corals produce an array of nasty, distasteful chemicals which are useful in defending them from predation. We also know that some molluscs which feed on soft corals, such as the egg cowries, and the aeolid Phyllodesmium longicirrum, re-use some of the soft coral's molecules for their own defence by storing them in parts of their bodies. This makes your observation of possible glands under the mantle edge particularly interesting as such glands are often not visible when the animal is collected and preserved.

Last year a paper was published by a joint group from Italy and China (Zhang et al, 2006) reporting a number of possible dietary metabolites in Dermatobranchus ornatus. They linked these metabolites with similar compounds in a gorgonian, Muricella sp.  from the same locality, and suggested that the nudibranch was transforming and bio-accumulating some useful dietary metabolites from the gorgonian into selected body parts as defensive substances.

Your 'glands' could well be where the Dermatobranchus is storing these metabolites. Thanks for this very interesting observation, which I am sure will be followed up by the Italian research group.

  • Zhang, W., Gavagnin, M., Guo, Y-W.,  Mollo, E. & Cimino, G. (2006)  Chemical Studies on the South China Sea Nudibranch Dermatobranchus ornatus and Its Suggested Prey Gorgonian Muricella sp. Chinese Journal of Organic Chemistry, 26 (12): 1667-1672

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Apr 8). Comment on Dermatobranchus ornatus - Feeding & mantle glands by Gaetan White. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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