Re: Color forms of Okenia mediterranea

March 8, 2006
From: Cristian Magnani

Concerning message #16033:

Dear Bill
Thanks for your interest. I was very surprised to know that Okenia mediterranea doesn't live on gorgonians. It says in a book by Egidio Trainito " Nudibranchi del Mediterraneo" ( Mediterranean nudibranches) that they do. Actually this books lacks some real pictures and the Okenia is depicted as a colour painting on [a photo of a] branch of deep water red gorgonian ( Paramuricea clavata). in another book "Mediterranen Fauna" by G. Nikiforos Okenia mediterranea is said to lives in "coral zone" the area deeper than 30 meters where gorgonians, encrusting sponges and coelentherates like Leptosammia purvoti lives.

I do believe you are right about the Alcyonidium bryozoan. I do believe the Okenia in my earlier photos are feeding upon Alcyonidium gelatinosum and the white hexagonal structure is the Alcyonidium skeleton while the living bryozoan is below the Okenia. Here is another photo where I think it is easier to see.
Thanks for your precious help Bill !
Nice dives!

Magnani, C., 2006 (Mar 8) Re: Color forms of Okenia mediterranea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Cristian,
I had noticed a couple of the 'photos' in Egidio Trainito's book looked as though the nudibranch was a pianting on a background photo of a 'real' food item. He really should mention this in the caption as I was not sure in the case of Okenia mediterranea, and so it reinforces an error. The idea that this species feeds on gorgonians seems to have started in the Atlas of Mediterranean nudibranchs.

I hadn't realised the brownish-white region in your photos was also part of the bryozoan colony. Thanks for the extra photo. It's nice to be able to confirm the report by Lucas Cervera and his colleagues that this species feeds on Alcyonidium.

  • Cattaneo-Vietti, R., R. Chemello, & Giannuzzi-Savelli, R. (1990) Atlas of Mediterranean nudibranchs [Atlante dei nudibranchi del Mediterraneo], 264 pp., 14 pls. La Conchiglia: Rome.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Mar 8). Comment on Re: Color forms of Okenia mediterranea by Cristian Magnani. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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