Description: This nudibranch has a pale fawn coloration with some superficial orange pigment on the dorsum. The numerous cerata have white cnidosacs which are particularly large in the anterior cluster, giving a white collar or ruff to the animal. There is little surface pigment on the ceratal surfaces. The rhinophores have paler pigment increasing in density towards the tips.

Habitat: This is an intertidal species which feeds on a variety of sea anemones, particularly Cereus pedunculatus, Diadumene cincta and Sagartia elegans. It has direct development, i.e. with no veliger larval stage. The spawn is a convoluted spiral thread containing large eggs.

Distribution: Found only in the south and west of the British Isles, with a few records from western Ireland. This species extends along the south coast of England to the Isle of Wight and the Medina estuary. On the French Atlantic coast it is frequent but sporadic in occurrence. It is also found in the Mediterranean Sea.

Key Identification Features:

• Body with sparse superficial pigment.
• First cluster of cerata with elongated cnidosacs giving white "ruff".

Distribution Map from NBN: Aeolidiella alderi at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Aeolidiella alderi at iNaturalist World Species Observations database.

WoRMS: Aeolidiella alderi at World Register of Marine Species. Accepted name: Aeolidiella alderi (Cocks, 1852). AphiaID: 138710.

Classification: Biota; Animalia; Mollusca; Gastropoda; Heterobranchia; Euthyneura; Ringipleura; Nudipleura; Nudibranchia; Cladobranchia; Aeolidioidea; Aeolidiidae; Aeolidiella