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

A sea slug (Runcina coronata)

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



Runcina coronata is a shell-less species up to 6 mm long. The head is blunt at the front, with no tentacles. The body is dark brown, with paler areas on the head. Three small posterior gills protrude at the right hand end of the mantle which distinguish the genus from similar sea slugs e.g. Limapontia senetra.

Recorded distribution in Britain and Ireland

Recorded from the south coast of England, Wales, the Isles of Scilly, western Scotland and north to the Orkneys.

Global distribution

From the Atlantic and Mediterranean coasts of France and Portugal.


Occurs intertidally in clear coralline rockpools.

Depth range


Identifying features

  • Up to 6 mm long.
  • Body dark brown or olive green with paler areas on head.
  • Head truncate at front, with no tentacles.
  • Two curved white lines across the body, one just behind the head and one at the posterior end of the body.
  • Three simple gills project from beneath mantle rim on right hand side.

Additional information

Runcina coronata and the sacoglossan Limapontia senestra are the only European opisthobranchs in which the shell makes no appearance at any stage in its embryonic development (Thompson, 1976). Spawning in Runcina coronata occurs in the spring months. The egg masses contain 20-30 eggs (Thompson, 1976).

Listed by

- none -

Further information sources

Search on:


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

  4. MarLIN (Marine Life Information Network), 2005. SEArchable BEnthic Data (SEABED) Map [on-line]. Data Access Sub-programme, Marine Life Information Network for Britian and Ireland,

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

  6. Rudman, W.B., 1999b. Runcina coronata [on-line].,

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

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


This review can be cited as:

Oakley, J.A. 2007. Runcina coronata 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 17-08-2018]. Available from:

Last Updated: 07/06/2007