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

A sea slug (Tritonia nilsodhneri)

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



A slender sea slug that grows up to 34 mm. It is pale salmon-pink or pure white in colour and has no markings on its body. It is extremely well camouflaged on its prey, the sea fan Eunicella verrucosa as it has eight pairs of gills along its back that closely resemble the feeding polyps.

Recorded distribution in Britain and Ireland

A south-westerly distribution in the British Isles with the most northern limit at St. John's Point, Co. Donegal (NW Ireland).

Global distribution



Found on its prey, the sea fan Eunicella verrucosa.

Depth range


Identifying features

  • Slender body without markings.
  • Six processes on the oral veil.
  • Approximately eight pairs of gills on the dorsum.
  • Rhinophores have smooth edged sheaths and branched tips.

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. Moore, J., 2002. An atlas of marine Biodiversity Action Plan species and habitats and Species of Conservation Concern in Wales, 2nd edn. Report to the Countryside Council for Wales, CCW Contract Science Report no. 509.

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


  1. 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.

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

  3. NBN (National Biodiversity Network) Atlas. Available from:

  4. OBIS (Ocean Biogeographic Information System),  2019. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2019-05-25


This review can be cited as:

Wilson, E. 2008. Tritonia nilsodhneri 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 25-05-2019]. Available from:

Last Updated: 17/04/2008