Aeolidiella alderi from Croatia

July 13, 2006
From: Mat Vestjens

Hello Bill,

In June this year I took the attached picture in Selce, Croatia. I believe this must be Aeolidiella alderi, but the colour is rather pale, compaired to earlier specimens I found. Could you confirm this species or do you have a different opinion.

Locality: Selce, 5 metres, Croatia, Adriatic sea, 03-06-2006. Length: 20 mm. Photographer: Mat Vestjens

Best regards,
Mat Vestjens

Vestjens, M.G., 2006 (Jul 13) Aeolidiella alderi from Croatia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Mat,
This is Aeolidiella alderi. The colour of the cerata is not a good character to use in most aeolids, because the colour of the digestive gland duct which runs up inside each ceras is dependent on the colour of the food they have been eating. Also if they have not eaten in a while, the colour can fade considerably so you get a very pale animal, as in your photo.

The best external character in A. alderi, which appears to be unique to this species, is the size of the cnidosac in the anterior row of cerata. In the close-up alongside you can clearly see that the cnidosac in each of the anterior cerata is proportionally much larger - occupying more than half the ceratal length - when compared with other cerata in the animal. Because these larger white cnidosacs replace much of the digestive gland in these anterior cerata, the cerata appear white, and make the aeolid look as though it has a white collar or 'ruff' around its neck.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Jul 13). Comment on Aeolidiella alderi from Croatia by Mat Vestjens. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Aeolidiella alderi

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