A sea slater (Stenosoma lancifer)

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



A small elongate isopod. The males can be up to 22 mm long while the females are smaller. It has fairly small eyes, positioned either side of the head and it is brown in colour. Two thirds of the body is segmented with legs. The first segments of the legs are expanded (coxal plates) which are small and triangular. The body then narrows sharply to an elongate projection (pleotelson) which is shaped like an ink pen nib.

Recorded distribution in Britain and Ireland

Recorded only on the south western coasts of the British Isles.

Global distribution

Found southwards from the British Isles to the Mediterranean.


Synisoma lancifer can be found amongst algae and under stones, particularly around low water of spring tides.

Depth range


Identifying features

  • Chitinous body dorso-ventrally flattened, up to 22 mm in length.
  • Long elongate body brown in colour.
  • Small lateral eyes.
  • All thoracic (pereon) segments have conspicuous lateral expansions (coxal plates).
  • Coxal plates triangular with lateral borders appearing more or less symmetrically serrated.
  • Pleotelson (tail piece) two thirds of the body length and narrowing sharply to an elongate median projection, similar to an ink pen nib in appearance.
  • Telson has deeply concave sides.

Additional information

Similar to Synisoma acuminatum, which is also found in the south west of the British Isles but Synisoma lancifer has broadly rounded pereon segments, with conspicuous coxal plates (see Naylor, 1972).

Listed by

- none -


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

  2. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  3. 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.]

  4. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid

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


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

  2. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.

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

  4. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-06-23


This review can be cited as:

Neish, A.H. 2006. Stenosoma lancifer 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 23-06-2024]. Available from: https://www.marlin.ac.uk/species/detail/1900

Last Updated: 10/11/2006