Aeolidiella alderi
(Cocks, 1852)

Family: Aeolidiidae


British Isles to Mediterranean Sea


UPPER: Sète, southern France, Mediterranean Sea. [Dive site : étang de Thau] Depth: 3m , Size: 1 cm. December 2000. Photo: J-P. Bielecki. (Note purple eggsacs of copepod parasite).
LOWER: Animal showing characteristic white 'ruff' or collar. Bay of Algeciras (Strait of Gibraltar, southern Spain) at 1 - 6 m. depth. Size: 15 mm. Place: Las Lajas Reef. August, 1999. Photo: Alma Sánchez

The cerata in the anterior-most row differ from the rest in having the digestive gland duct only reaching halfway up. The whitish cnidosac are consequently larger, filling the upper half of these cerata and giving the animal the appearance of having a whitish collar or "ruff". Tardy (1964) has observed that the larger nematocysts in these larger cnidosacs are fired into sea anemones to help subdue them. This species feeds exclusively on sea anemones. It is hard to diferentiate in shape and colour from A. glauca, but it has a quite different reproductive behaviour with A. glauca having planktotrophic larval development while A. alderi has direct development, with no planktonic larval stage. See Bernard Picton's message differentiating A. alderi, A. sanguinea and A. glauca.

• Thompson, T.E. & Brown, G.H. (1984) Biology of Opisthobranch Molluscs, Vol 2 Ray Society: London.

Authorship details
Rudman, W.B., 2001 (February 18) Aeolidiella alderi (Cocks, 1852). [In] Sea Slug Forum. Australian Museum, Sydney. Available from

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