A sea slater (Idotea emarginata)

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



A dorso-ventrally flattened crustacean with an elongated rounded oblong shaped body. Males range in length from 7 to about 30 mm and females from 9 to 18 mm. Males brown in colour, occasionally with white markings. Females generally darker but with white bands along the sides of the body or alternating white and darker transverse bands. The distinct head bears two dorso-lateral eyes, a pair of short antennules, and a pair of antennae. Most of body is taken up by a thorax composed on seven sections (somites). The body ends in a short abdomen (two somites) and a distinct tail-piece (the pleotelson). The pleotelson in adults is characteristic, with slightly convex sides and a posterior end that is rounded in juveniles but bears two side processes in the adult giving a notched or emarginate appearance.

Recorded distribution in Britain and Ireland

Probably distributed all around the coasts of Britain and Ireland but poorly represented in surveys.

Global distribution



A sublittoral species living on seaweeds but also found on cast-up seaweed in the intertidal.

Depth range


Identifying features

  • Dorso-ventrally flattened and oblong, oval body.
  • Abdomen (pleon) consists of two complete somites and one partial suture.
  • Pleotelson bears two processes in adults giving a notched or emarginate appearance.
  • Antennule extends beyond the third section of the antenna.
  • Antennal flagellum longer than its peduncle and up to a fifth of the body length.
  • Tops of the legs bear broad coxal plates in the adult that are the full length of somites 2 or 3 to 7.

Additional information

No text entered

Listed by

- none -


  1. Bruce, J.R., Colman, J.S. & Jones, N.S., 1963. Marine fauna of the Isle of Man. Liverpool: Liverpool University Press.

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

  3. MBA (Marine Biological Association), 1957. Plymouth Marine Fauna. Plymouth: Marine Biological Association of the United Kingdom.

  4. Naylor, E., 1972. British marine isopods. London: Academic Press. [Synopses of the British Fauna, no. 3.]

  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.


  1. Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01

  2. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  3. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-05-18


This review can be cited as:

Tyler-Walters, H., 2005. Idotea emarginata A sea slater. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 18-05-2024]. Available from: https://www.marlin.ac.uk/species/detail/2105

Last Updated: 10/01/2005