Confusingly, the "ocean quahog" is a different species, Arctica islandica, which, although superficially similar in shape, is in a different family of bivalves: it is rounder than the hard clam, usually has a black periostracum, and there is no pallial sinus in the interior of the shell.

The smallest legally harvestable clams are called countnecks or peanuts, next size up are littlenecks, then topnecks.

[5][6] Native polities on the eastern Atlantic seaboard made valuable beads called wampum from the shells, especially those colored purple; the species name mercenaria is related to the Latin word for commerce.

Today people living in coastal New England still use Algonquian words for the clam, as they have done for thousands of years.

These are quite similar to common "wild type" Mercenaria clams, except that their shells bear distinctive markings.

[7] Hard clams are quite common throughout New England, north into Canada, and all down the Eastern seaboard of the United States to Florida; but they are particularly abundant between Cape Cod and New Jersey, where seeding and harvesting them is an important commercial form of aquaculture.

The species has also been introduced and is farmed on the Pacific coast of North America and in Great Britain and continental Europe.

[9] This research is fueled by the need to inform aquaculturists, who suffer financially because of the mortality rates in clams that QPX inflicts and the ensuing years in which runs must be left fallow to clear the disease.

Although QPX disease was first recorded on the Atlantic coast of Canada in the early 1960s, it did not become a major economic problem until its appearance in cultured clams at Prince Edward Island, Massachusetts in 1992, and Virginia in 1997.