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Hard Clam or Quahog
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Bivalvia Order: Veneroida Family: Veneridae Genus: Mercenaria Species: M. mercenaria
Binomial name
Mercenaria mercenaria Linnaeus, 1758

The hard clam (Mercenaria mercenaria) or quahog, is a bivalve mollusc native to the eastern shores of North America, from Prince Edward Island to the Yucatán Peninsula. Older sources may give it the systematic name Venus mercenaria. It is one of many unrelated bivalves referred to as clams. Confusingly, the ocean quahog is a different species, Arctica islandica.

The hard clam has many alternative names in addition to quahog. It is also known as the Northern quahog, round clam, or chowder clam. Furthermore, in fishmarkets there are specialist names for different sizes of hard clam. The smallest clams are called countnecks, next size up are littlenecks, then topnecks. Above that are the cherrystones, and the largest are called quahogs or chowder clams.

Of all these names, the most distinctive is quahog (pronounced /ˈkwɔːhɒg/ "KWAW-hog", /ˈkoʊhɒg/ "KO-hog", or /kwəˈhɒg/ "kwa-HOG"}}). This name comes from the Narragansett word "poquauhock" (the word is similar in Wampanoag and some other Algonquian languages), and is first attested in North American English in 1794.^[1] As New England Indians made valuable beads called wampum from the shells (especially the purple color), the species name mercenaria is related to the Latin word for "money."

Many areas where aquaculture is highly important have bred specialized versions of these clams, in an attempt to distinguish themselves in the marketplace. These clams are quite similar, except that their shells bear distinctive markings; for example those from Wellfleet, Massachusetts have pronounced wavy or zigzag lines on their shells, which are meant to be reminiscent to a line of Ws running across the shell — an attempt to capitalize on the town's reputation for oysters. Those that have been specially bred with markings have more recently been breeding with wild stocks, so it is not uncommon for wild clams to have these markings.

Hard clams are quite common throughout New England, north into Canada, and all down the Eastern seaboard of the United States to Florida, but are particularly abundant between Cape Cod and New Jersey, where seeding and harvesting them is an important commercial form of aquaculture; for example, the species is an important member of the suspension-feeding, benthic fauna of the lower Chesapeake Bay, while tiny Rhode Island, situated right in the middle of "quahog country," has supplied a quarter of the USA's total annual commercial quahog catch. The quahog is the official shellfish of the state of Rhode Island List of U.S. state shells. The species has also been introduced and is farmed on the Pacific coast of North America and in Great Britain and continental Europe. It reproduces sexually.

Quahog Parasite Unknown (QPX) is a parasite that affects Mercenaria. While little is known about the disease, research is currently underway in several laboratories^{[attribution needed]}. 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.

Steamed Clams

In coastal areas of New England, restaurants known as raw bars specialize in serving littlenecks and topnecks raw on an opened half-shell, usually with a cocktail sauce with horseradish, and often with lemon. Sometimes, littlenecks are steamed and dipped in butter, though not as commonly as their soft-shelled clam cousin, the "steamer." Littlenecks are often found in-the-shell in sauces, soups, stews, "clams casino" or substituted for European varieties such as the cockle in southern European seafood dishes. The largest clams, quahogs or chowders and cherrystones (with the toughest meat), are used in such dishes as clam chowder and stuffed clams or are minced and mixed into dishes that use the smaller, more tender clams.

The term "red tide" refers to an accumulation of a toxin produced by marine algae. Filter-feeding shellfish — such as clams, oysters, and mussels — are affected. The toxin affects the human central nervous system. Eating contaminated shellfish, raw or cooked, can be fatal.

Some algal blooms make the seawater appear red, but red tide blooms do not always discolor the water nor are they related to tides.

Clams bought from a market should always be safe as commercial harvesters are extremely careful about red tides: They close beds that are even remotely threatened and keep them closed for up to three or four weeks after they are clean of any red tide. Any commercial clam fisher who breaks these rules is in line for a major fine in the first instance and will most likely have their license to harvest or sell clams revoked; furthermore they are liable for any damages.