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

A bivalve mollusc (Thracia villosiuscula)

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



Thracia villosiusucla is a rather flat sub-rectangular bivalve. It can be up to 3 cm long and shell white in colour and quite brittle. The surface of the shell has fine granulation and this can be seen with a X10 hand lens. The shiny covering layer of shell (periostracum) can be brown and sometimes reddish-brown. The posterior margin is obliquely truncated and slightly gaping. The beak (umbo) of the left valve sits in a hole in the beak of the right valve, and the right valve is slightly larger and more convex than the left. The bivalve does not contain either cardinal or lateral teeth.

Recorded distribution in Britain and Ireland

Reported from most parts of the British Isles but uncommon. The extent of distribution is uncertain because of the difficulty of separating Thracia villosiuscula from Thracia phaseolina.

Global distribution

From Norway south to the Mediterranean.


Thracia villosiuscula burrows deeply in coarse sands and coarse fine gravels from the lower shore and shallow sublittoral to depths of about 55 m.

Depth range


Identifying features

  • Brittle, white bivalve up to 3 cm long.
  • Obliquely truncate posterior margin, slightly gaping.
  • Right valve slightly larger and more convex.
  • Umbo of left valve sitting in a hole in the umbo of the right.
  • Hinge line with a small triangular chondrophore but neither cardinal or lateral teeth are present.
  • Proportionally longer posterior hinge line.

Additional information

Difficult to distinguish from Thracia phaseolina but can be told apart by finely granular shell surface, granulations visible with X10 hand lens.

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. Hayward, P.J. 1994. Animals of sandy shores. Slough, England: The Richmond Publishing Co. Ltd. [Naturalists' Handbook 21.]

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

  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. Tebble, N., 1976. British Bivalve Seashells. A Handbook for Identification, 2nd ed. Edinburgh: British Museum (Natural History), Her Majesty's Stationary Office.


This review can be cited as:

Neish, A.H. 2005. Thracia villosiuscula A bivalve mollusc. 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 21-09-2018]. Available from:

Last Updated: 17/10/2005