Dermatobranchus ornatus - Feeding & mantle glands

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