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

White piddock (Barnea candida)

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



Barnea candida has a white shell with a yellowish or light brown periostracum, and has pronounced sculpturing anteriorly composed of concentric ridges crossed by ribs with spines. The shell is fragile, narrowly elongate and oval, up to 6.5 cm in length. Barnea candida have large foot muscles and visceral mass, and are unable to retract completely within their shells. The anterior and posterior margins are rounded. The hinge line has a slender projection (apophysis) just below the beak of each valve which serves as the attachment area for the large foot muscles. The umbones are positioned in the anterior third of the shell with an accessory plate, the protoplax, placed dorsally in front of them. The margin is crenulate with spines about the posterior pedal gape, smooth elsewhere. The siphons of Barnea candida are of equal length and united. These can reach 4 to 5 times the length of the shell. The inhalent siphon has 10 to 12 large, and several small, hairs surrounding its opening whilst the exhalent siphon has none. Both siphons are pale brown in colour and minutely papillose, and are tipped with a narrow band of red brown.

Recorded distribution in Britain and Ireland

Occurs around the southern half of Britain but almost entirely absent from the north of Britain and the coast of Ireland.

Global distribution

Occurs from Norway south to the Mediterranean and west Africa.


Burrows into wood, peat and soft rocks on the lower shore and sublittoral.

Depth range


Identifying features

  • Fragile, date-shaped shell up to 6.5 cm in length.
  • A single dorsal plate, the protoplax, lies in front of the umbones.
  • Anterior and posterior margins rounded.
  • Posterior margin gapes.
  • Radiating ribs bear spines anteriorly.
  • A slender calcareous projection (apophysis) below both beaks.
  • The siphons are united and may extend 4 to 5 times the length of the shell.

Additional information

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Further information sources

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

  2. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

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

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

  5. 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.]

  6. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

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

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

  9. Turner, R.D., 1954. The family Pholadidae in the western Atlantic and the eastern Pacific Part 1 - Pholadinae. Johnsonia, 3, 1-64.


This review can be cited as:

Ballerstedt, S. 2006. Barnea candida White piddock. 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 25-09-2018]. Available from:

Last Updated: 30/05/2006