Smooth nut clam (Ennucula tenuis)

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



A bivalve with a thin, triangular shell up to 1.3 cm in length. Both valves are similar in size and shape but are slightly asymmetrical, with the beak positioned behind the mid-line. The inside of the shell is nacreous (iridescent). The outer surface of the shell is white to a bluey grey but can be covered with a yellow, greenish-yellow, or dark brown layer (periostracum). The outside of the shell bears fine radiating grooves (striations) with slightly bolder concentric lines.

Recorded distribution in Britain and Ireland

Widespread around Britain and Ireland but absent from the English Channel, off the coast of south east England and western coasts of Ireland.

Global distribution

Ennucula tenuis is widely distributed in the northern hemisphere, from Greenland and Barents Sea, south to Gibraltar and the Florida Straits, and from the Alaskan Arctic and Siberia, south to California and Japan. It is also found in the Mediterranean.


Ennucula tenuis inhabits sandy mud, mud, and muddy gravel inshore in ca 10 m down to depths of around 200 m.

Depth range

Inshore in 10 m to outer continental shelf depths of up to 200 m

Identifying features

  • Triangular in outline.
  • Shell up to 1.3 cm in length and the height is approximately 75% of the length.
  • Shell bears faint radiating striations, visible with a hand lens, and slightly bolder concentric lines.
  • Both valves are similar in size and shape (equivalve).
  • The valves are asymmetrical with the beak positioned behind the mid-line (inequilateral).
  • Outer shell is white to bluey grey and the inner shell is nacreous (iridescent).
  • The hinge line has 16-18 teeth in the anterior group and 6-10 posteriorly.
  • The periostracum is glossy yellow, greenish-yellow or dark brown.

Additional information

Ennucula tenuis is a sub-surface feeder that plays an important role in ecosystems, due to its bioturbation activity.

Listed by

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  1. Bour, A., Haarr, A., Keiter, S. & Hylland, K., 2018. Environmentally relevant microplastic exposure affects sediment-dwelling bivalves. Environmental Pollution, 236, 652-660. DOI
  2. De Kluijver, M.J., Ingalsuo, S.S. & de Bruyne, R.H., 2021. Mollusca of the North Sea. Marine Species Information Portal. Leiden, The Netherlands: ETI Bioinformatics.  Available from:

  3. Oliver, P.G., Holmes, A.M., Killeen, I.J. & Turner, J.A., 2016. Marine Bivalve Shells of the British Isles. Amgueddfa Cymru - National Museum Wales. Available from: [Cited:  3 July 2018].

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


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

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

  3. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-06-12


This review can be cited as:

Lloyd, K.A., 2021. Ennucula tenuis Smooth nut clam. 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 12-06-2024]. Available from:

Last Updated: 22/09/2021

  1. Bivalve
  2. Mollusc
  3. Ennucula
  4. Nuculoma
  5. Nucula
  6. Smooth nutclam