A bivalve mollusc (Thracia villosiuscula)

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



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 -


  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. 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.

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


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland - restricted access. Occurrence dataset: https://doi.org/10.15468/4bsawx accessed via GBIF.org on 2018-09-25.

  3. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) records for Great Britain and Ireland. Occurrence dataset: https://doi.org/10.15468/aurwcz accessed via GBIF.org on 2018-09-25.

  4. Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: http://www.ericnortheast.org.ukl accessed via NBNAtlas.org on 2018-09-38

  5. Merseyside BioBank., 2018. Merseyside BioBank (unverified). Occurrence dataset: https://doi.org/10.15468/iou2ld accessed via GBIF.org on 2018-10-01.

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

  7. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-07-14

  8. Outer Hebrides Biological Recording, 2018. Invertebrates (except insects), Outer Hebrides. Occurrence dataset: https://doi.org/10.15468/hpavud accessed via GBIF.org on 2018-10-01.


This review can be cited as:

Neish, A.H. 2005. Thracia villosiuscula A bivalve mollusc. 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 14-07-2024]. Available from: https://www.marlin.ac.uk/species/detail/1898

Last Updated: 17/10/2005