The diet of Onchidoris

April 22, 2001
From: Brian Tarbox

Interested in the diet of Genus Onchidoris, east coast of the US.
Thank you
Brian Tarbox

Tarbox, B., 2001 (Apr 22) The diet of Onchidoris. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Brian,
I would prefer the Forum to be a means of spreading information both ways. For example, when someone sends in a photo for identification I am happy to attempt an identification and hopefully in return we will all get some information to increase our knowledge on where the species lives, colour variation etc. So with your question, is there any chance of some information from you in return? There seems to be quite a gap in out knowledge of the opisthobranch fauna of the east coast of North America, so any information from you on why you are interested in east coast Onchidoris would be of value. For example, if you are studying them and have photos of them I would love to be able to increase the Forum's coverage of that east coast fauna.

I know very little, and can find very little about the genus on the east coast of North America. Probably the best source of information would be Sherman Bleakney's 1996 Seaslugs of Atlantic Canada and the Gulf of Maine. In that he records two species, O. bilamellata (Linnaeus, 1767) and O. muricata (Muller, 1776) neither of which are represented on the Forum. O. bilamellata is rather unique in feeding on barnacles. It usually hides under rocks at low tide and crawls up to the barnacle zone when the tide is in, to rip of one of the barnacle's valves and feast on the animal within. O. muricata on the otherhand is more typical of the onchidorids, feeding on colonial bryozoans such as Electra and Membranipora.

It may be superfluous, since I don't know what your interest is, but one problem with studying these animals is identifying them in the field and distinguishing them from related species of the genus Adalaria. Characters such as the radular morphology, the size and number of eggs and the type of larval development are often needed to be sure of an identification - and these are not the easiest characters to use in the field.

Look forward to hearing from you,
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Apr 22). Comment on The diet of Onchidoris by Brian Tarbox. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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