Aeolidiella alderi and parasite

February 20, 2001
From: Jean-Pierre Bielecki

Dear Bill
Here are some pictures of an aeolid I suppose to be Aeolidiella alderi found :

in Mediterraean Sea, December 2000
Dive site : étang de Thau, Sète, southern France. Depth: 3m , Size: 1 cm.

This is the first time I have seen this purple extension on its back which I suppose is its digestive gland. What is its exact function. Is it a permanent or temporary structure and is it normal?
Best regards.
Jean-Pierre

bielecki.jeanpierre@free.fr

Bielecki, J-P., 2001 (Feb 20) Aeolidiella alderi and parasite. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3829

Dear Jean-Pierre,
As you will see in a separate message, Bernard Picton has confirmed this is A. alderi. The purple extensions are very interesting. They are not part of the aeolid but are the egg sacs of a crustacean parasite which is living in the body cavity of the aeolid. I am planning to put some information on the Forum concerning crustacean parasites when I get a moment.

There are a number of examples of parasites and 'commensals' already illustrated on the Forum. I have added an enlargement here [on right] of Daniel Geiger's photo of Spurilla neapolitana from Banyuls sur Mer, Mediterranean Coast, France, 1990. Four purplish white egg sacs can be seen amongst the cerata. Also have a look at the Symbiosis & Commensalism page and the Parasite page for some general information. See also the page on Ismaila, a common nudibranch parasite in South America. There are a number of photos on the Forum of egg masses protruding from aeolids in a very similar manner to the ones in your photo. There is also a photo in a message from Erwin Koehler, which also shows these egg masses in S. neapolitana from Spain.

Best wishes
Bill Rudman

Rudman, W.B., 2001 (Feb 20). Comment on Aeolidiella alderi and parasite by Jean-Pierre Bielecki. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3829

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