Aeolidiella alderi from sthn England

May 13, 2005
From: Judith Oakley

Can you have a look at these photos and let me know if this is a grey sea slug or could it possibly be Aeolidiella glauca? It doesn't seem to have the typical 'v' behind the head of the grey, and the 'fur' isn't parted down the back. It was found at Batten Bay, near Plymouth and had a yellowy/orange tinge.

Locality:  Batten Bay, nr Plymouth, Devon, England. Depth: lower shore.
Length: 1 inch. 8 May 2005. Intertidal under rock. Photographer: Judith Oakley

Thank you
Judith Oakley
Marine Biological Association of UK and Ireland

Oakley, J.A., 2005 (May 13) Aeolidiella alderi from sthn England. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Judith,
I am afraid I am not sure what you mean by a 'grey sea slug' - common names are not very universal. I am pretty sure your animal is Aeolidiella alderi. One way of distinguishing A. alderi from similarly shaped and coloured aeolid nudbranchs is that the most anterior row of cerata appear to be shorter than the other cerata and usually white. This forms what Bernard Picton [message #3845] has described as a 'ruff of white'. If you look at the close-up of the 'ruff' you can see the opaque cnidosac in these shortened cerata are much larger than usual, and occupy more than half the length of each ceras, giving them their white colouration.

A white ruff is of course a reference to the high decorative collar worn in Elizabethan times, so this is a very appropriate species to find in Plymouth, with its naval connections with Sir Francis Drake and Queen Elizabeth 1.

Best wishes,
Bill Rudman

Rudman, W.B., 2005 (May 13). Comment on Aeolidiella alderi from sthn England by Judith Oakley. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Aeolidiella alderi

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