All clams are mollusks, part of a phylum of invertebrates including squids and snails. They have soft, unsegmented bodies.
Clams are differentiated at the family level of taxonomy, which precedes genus and species. Clams are bivalve filter-feeders, obtaining their food by passing ocean water through their bodies. Clam shells are made of calcium carbonate varying in strength and shape. A soft-shell clam can be crushed easily by most children. Breaking a hard-shell clam exoskeleton takes a hammer, or a stomped foot. Broken soft clamshells are insignificant as a beach hazard. Broken hard clamshells are razor-sharp in the manner of metamorphic rock, as found in Cyprus or Italy. They will slice open an errant foot in less than a second.
Here is a list of the most commonly-eaten American clams, and a brief description of each.
Ensis directus: common to the East Coast of the United States, razor clams are of the family Solenidae and also called Atlantic jackknife clams. They are not generally sought out, and most often consumed as bycatch. The flesh is tough, and requires pulverizing and/or marinating in an acidic compound to break down proteins and make the meat easier to chew. They are often confused with another razor clam, the pacific razor clam, Siliqua patula, which is quite tasty (I like them prepared with black bean sauce)), or the smaller Atlantic razor clam, Siliqua costata.
Mya arenaria: these most-prized clams for summer dining are known by many different English terms, including longnecks and common sand gapers (owing to the manner in which they eject water into the air from under the sand). They are of the family Myidae and very easy to prepare. Leaving the clams overnight in seawater so that they spit out any sand, then boiling them whole in a large pot is all that is necessary.
Mercenia mercenaria: this clam is the most-commonly harvested variety on the East Coast. They are of the family Veneridae, a reference to the Birth of Venus (Aphrodite) famous in Greek and Roman myth. Venus is said to have been born as an adult from the ocean, standing upon a large clam shell. In common speech, the smallest M. mercenaria are known as littlenecks. Hardshell clams two to three inches, of about five years old are known as cherrystones. Quahaugs are hardshell clams larger than 3.5 inches. They are never eaten raw, and most often minced for use in chowder or clam pie.
Panopea abrupta: this large clam is native to the Pacific, and can be found from Alaska to Baja California. In appearance it resembles an Eastern steamer clam, except seven or eight times larger. Geoducks, pronounced “gooey-ducks” are of the family Hiatellidae. They can reach twenty pounds and live up to one hundred fifty years. They are prized especially in the Pacific Northwest and in Japan, Hong Kong and China for the sweetness of their flesh.
Atlantic surf clams (Spisula solidissima) , some times called sea clams or simply surf clams are hard shelled clams found underwater even at low tide and they get up to about 8" long (20 cm). They naturally occur from Maine to Delaware and are farmed elsewhere.|