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

A sea slug (Hero formosa)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



A beautiful and delicate species of sea slug with a single row of bushy, branched appendages down each side of the body and across the front of the head. It can grow up to 38 mm in length and is pale pinkish-brown in colour with white spots scattered down the body and a white centre line along the back. The head bears a pair of greatly enlarged curved oral tentacles.

Recorded distribution in Britain and Ireland

Most recent records are from the Isle of Man, the west coast of Scotland, near Oban and the Rockall Trough.

Global distribution



Found on wrecks and muddy sand habitats with scattered shell and rocks. Has a considerable depth range.

Depth range


Identifying features

  • Branching ceratal processes along sides of body and across front.
  • White centre line down middle of back.
  • Large propodial tentacles at the front of the foot.
  • Smooth rhinophores with white tips lie behind the most anterior pair of cerata.
  • Anal papilla is lateral, on right side.

Additional information

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Listed by

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Further information sources

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  1. 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.]

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

  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:

Wilson, E. 2005. Hero formosa 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 20-08-2018]. Available from:

Last Updated: 31/10/2005