Biodiversity & Conservation

Hard-shell clam - Mercenaria mercenaria

Mercenaria mercenaria

Image National Museum Wales - External view of Mercenaria mercenaria valve. Image width ca 12 cm.
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Distribution map

Mercenaria mercenaria recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Mercenaria mercenaria is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Mollusca Snails, slugs, mussels, cockles, clams & squid
Class Bivalvia Clams, cockles, mussels, oysters, and scallops
Authority Linnaeus, 1758
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland This species has a limited distribution in British waters with isolated records from Burnham-on Crouch, the south coast of England, Pembrokeshire and Loch Sunart, Scotland. There are no records in Ireland.
Habitat information icon Habitat information Found buried in muddy sediment on the lower shore and shallow sublittoral and in bays and estuaries. Prefers sandy environments to depths of 15 m.
Text page icon Description Mercenaria mercenaria has a thick shell, roughly triangular in shape overall, light brown to grey in colour with a violet border and often with varying concentric bands on the shell . These concentric bands are conspicuous and are closely spaced around the margins but more widely spaced around the umbo. The inner shell surface is shiny with a purplish-blue tinge around the muscle scars. The sculpture of the shell consists of thin concentric ridges that are sharp and raised in early growth stages but worn away in older shells. It can grow up to 12 cm in length. The beak extends well beyond the the main shell. The pallial line is short and triangular with a finely rippled inner margin. Each valve has three conspicuous teeth. The internal anatomy is distinctive. The exhalent and inhalent siphons are joined with a fringe of tentacles around the inhalent siphon. The siphons are yellowish or brownish orange at the ends and often streaked with dark brown or opaque white. The foot is large and white in colour.
Identifying features
  • The shell has a sculpture of concentric grooves and striations.
  • The shell is light brown to grey in colour forming fine bands.
  • The inner shell surface is shiny with a purplish-blue tinge around the muscle scars.
  • Grows up to 12 cm in length.
  • Each valve has three conspicuous teeth.
  • Jointed siphons with a fringe of tentacles on the inhalent siphon.
  • A large foot that is white in colour.
Additional information icon Additional information Commonly known as the Quahog and used to make clam juice. This is a non-native species unsuccessfully introduced into British waters several times since the middle of the nineteenth century. The first live specimen was found in 1864 in the Humber. Merceneria mercenaria was successfully introduced from the USA into Southampton Water in 1925. Due to the colouration of the shell, the native American Indians utilised the shell as 'wampun' for use as currency, hence its scientific name.

This review can be cited as follows:

Michelle Carter 2005. Mercenaria mercenaria. Hard-shell clam. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 24/05/2013]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=3792>