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

A sea slug (Dendronotus frondosus)

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



Dendronotus frondosus is a large, up to 10 cm long, laterally compressed sea slug with variable colouring. It can be white or pink with mottled brown, red or yellow pigment. Along the back there are paired, branched processes called cerata that act as gills. In between the cerata there are smaller processes that are also branched. On the front edge of many sea slugs is a flap of tissue called the oral veil, which bears branched processes in Dendronotus frondosus. The antenna-like rhinophores are sheathed in tissue and these sheaths terminate in branched processes. Between the branches at the end of the rhinophore sheaths are the ends of the rhinophores themselves, which resemble ribbed pine cones in texture and shape.

Recorded distribution in Britain and Ireland

Common on all British and Irish coasts.

Global distribution



Adult Dendronotus frondosus are found in the shallow sublittoral on the hydroids Tubularia larynx and Tubularia indivisa. Juveniles can be found on the hydroids Obelia sp., Sertularia sp., Halecium sp., and Hydrallmania falcata

Depth range


Identifying features

  • White or pale pink mottled with brown, red or yellow pigment.
  • Nine pairs of highly branched cerata on dorsal surface.
  • Oral veil with highly branched processes.
  • Rhinophores are sheathed, terminating in arborescent (tree-like) processes and a lamellate, corkscrew-like appendage.

Additional information

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Further information sources

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  1. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  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. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

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

  5. 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.

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


This review can be cited as:

Neal, K.J. 2007. Dendronotus frondosus 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 21-09-2018]. Available from:

Last Updated: 31/05/2007