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

A sea slug (Rostanga rubra)

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



Rostanga rubra is usually bright scarlet in colour and up to 2 cm in length. The body is domed and warty.The deep red coloration is derived from the red sponges Microciona atrasanguinea and Ophlitaspongia papilla on which it feeds. There may be scattered black spots dorsally and a characteristic yellowish patch between the rhinopores. Two finger-like oral tentacles project from the sides of the head. The mantle bears many short, blunt tubercles dorsally, together with defensive spicules. Up to ten simple pinnate gills may be present in a tight circle, which retract into a deep pocket or cup.

Recorded distribution in Britain and Ireland

All British coasts except the southeast. Predominantly recorded on the west coasts of England and Wales.

Global distribution

Recorded north to western Norway and south to the Mediterranean.


This conspicuous species feeds on red sponges e.g. Microciona atrasanguinea and lives in shallow water. It occurs on the lower shore and shallow sub-littoral on rocky coasts.

Depth range


Identifying features

  • Usually bright red in colour but may be pale orange-yellow.
  • Black flecks and a yellowish patch between rhinopores.
  • Body domed and warty.
  • Ten short gills in tight circle.
  • Up to 2 cm long.
  • Two oral tentacles project from sides of the head.

Additional information

Spawns in June and July.

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. 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. Rudman, W.B., 2002b. Rostanga rubra [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. & Brown, G.H., 1984. Biology of Opisthobranch Molluscs, vol. II. London: Ray Society.


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset accessed via on 2018-09-25.

  2. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland - restricted access. Occurrence dataset: accessed via on 2018-09-25.

  3. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland. Occurrence dataset: accessed via on 2018-09-25.

  4. Fenwick, 2018. Aphotomarine. Occurrence dataset Accessed via on 2018-10-01

  5. Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1990 to 1994. Occurrence dataset: accessed via on 2018-10-01.

  6. National Biodiversity Network (NBN) Atlas website. Available from:

  7. OBIS,  2019. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2019-01-20


This review can be cited as:

Oakley, J.A. 2007. Rostanga rubra 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 20-01-2019]. Available from:

Last Updated: 24/01/2007