information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

A sea slug (Aeolidiella alderi)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.



This species has a flattened and slender shape with a length of up to 37 mm. Pale cream or fawn in colour, with superficial orange pigments on its back. There are 14-16 transverse rows of finger-like extensions (cerata) on either side of its back, ten of which are mobile & elongated. The tips of the cerata are white or pale in colour, particularly at the anterior end of the body, forming a white ruff around the body. Generally the cerata, rhinophores and oral tentacles are white or pale yellow, the colour increasing in density towards the tip. Oral tentacles are slightly longer than the rhinophores, which are smooth or slightly wrinkled but neither of which have lamella. The alimentary canal is visible, and its colour may vary depending on diet from pale green and pink to dark brown.

Recorded distribution in Britain and Ireland

Recorded from St. Abbs Harbour, east Scotland; Poole harbour and Plymouth Sound, England; Lough Hyne, Mulroy Bay and the Garvan Isles, Ireland, and Loch Sunart, west Scotland.

Global distribution



This is an intertidal species which feeds on sea anemones.

Depth range


Identifying features

  • Two oral tentacles, longer than rhinophores.
  • Numerous cerata.
  • Tips of the cerata are white or pale in colour, particularly at the anterior end of the body, forming a white ruff around the body.
  • The body is pale cream/fawn in colour.
  • Up to 37 mm in length.

Additional information

Spawn forms a convoluted spiral thread containing 200-1200 large eggs. Development is direct, i.e. there is no larval stage. Aeolidiella alderi feeds on a variety of sea anemonies mainly Cereus pedunculatus, Diadumene cincta and Sagartia species (Picton & Morrow, 1994). The body of Aeolidiella alderi is more slender than Aeolidia papillosa (Thompson & Brown, 1984).

Listed by

- none -

Further information sources

Search on:


  1. Crothers, J.H. (ed.), 1966. Dale Fort Marine Fauna. London: Field Studies Council.

  2. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  3. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  4. MBA (Marine Biological Association), 1957. Plymouth Marine Fauna. Plymouth: Marine Biological Association of the United Kingdom.

  5. Picton, B. E. & Morrow, C.C., 1994. A Field Guide to the Nudibranchs of the British Isles. London: Immel Publishing Ltd.

  6. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.

  7. Sanderson, W.G., 1996. Rare benthic marine flora and fauna in Great Britain: the development of criteria for assessment. Joint Nature Conservation Committee, Peterborough. JNCC Report, no. 240.

  8. Seaward, D.R., 1982. Sea area atlas of the marine molluscs of Britain and Ireland. Peterborough: Nature Conservancy Council.

  9. Thompson, T. E. & Brown, G. H., 1976. British Opisthobranch Molluscs. London: Academic Press. [Synopses of the British Fauna, no. 8.]

  10. Thompson, T.E. & Brown, G.H., 1984. Biology of Opisthobranch Molluscs, vol. II. London: Ray Society.

  11. Thompson, T.E., 1976. Biology of Opisthobranch Molluscs, vol. 1. London: The Ray Society.


This review can be cited as:

Rowley, S.J. 2007. Aeolidiella alderi A sea slug. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23-09-2018]. Available from:

Last Updated: 13/08/2007