A clam is an edible marine bivalve mollusc housed in two matched, roughly equal hinged shells that clap shut around a sweet, briny, faintly chewy body. The name covers dozens of species — the hard-shell quahog (Mercenaria mercenaria), sold by size as littleneck, topneck, cherrystone and chowder clam; the thin-shelled soft-shell "steamer"; the Manila clam; the giant razor and geoduck — most of them dug or dredged out of sand and mud. Sweeter and less iodine-sharp than an oyster, the clam is eaten raw on the half-shell, steamed by the bucket, simmered into chowder and tumbled with garlic and wine in pasta alle vongole.