Color forms of Okenia mediterranea

March 7, 2006
From: Cristian Magnani

Dear Bill,
Last April 30 2005 while diving on a cargo shipwreck out of Numana on the Italian Adriatic coast we spotted a pair of Okenia mediterranea. We were so glad we had the chance to take a few picture of a nudibranch we had never seen before over there and a stunning one also. Once at home I was very impressed to find out that this slug usually lives on gorgonian. One week later we went back and we found another Okenia mediterranea but in a different color form. Unfortunately i didn't take their length but it was in the 6-7 mm range.

Locality: Numana, 12 metres, Italy, Mediterranean Sea, 04 May 2005, inside iron shipwreck . Photographer: Cristian Magnani.

I send you photos of both color forms
Thanks
Best regards
Cristian

cristianmagnani@hotmail.com

Magnani, C., 2006 (Mar 7) Color forms of Okenia mediterranea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16033

Dear Cristian,
Thanks for your beautiful photos of the two colour forms. They certainly are quite different in colour. I see Luis Tocino has the yellow colour form on his website [http://www.ugr.es/~lstocino/] of Granada opisthobranchs, but has it identified as O. elegans, which is a bit puzzling.

I am also puzzled by the reference to it feeding on gorgonians as most species of Okenia feed on bryozoans and a few on ascidians. Also it has been reported feeding on the ctenostome bryozoan Alcyonidium mytili [see Cervera et al (1991). In your photo of the red-orange spotted colour form your animals are on a reddish encrusting bryozoan. Although ctenostome bryozoans are usually fleshy, non calcareous, arborescent bryozoans, I think Alcyonidium mytili is a pink encrusting form so you might have recorded it on its bryozoan food. Even if it is not that species, it is a bryozoan, and I am pretty sure its presence on the bryozoan is not a coincidence. All in all you photos raise a number of interesting points. Are these colour forms the same species? Does this species really eat gorgonians? What is the bryozoan in your photo?

Lets hope someone can help,with some answers.
Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Mar 7). Comment on Color forms of Okenia mediterranea by Cristian Magnani. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16033

Factsheet

Okenia mediterranea

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