White clam

In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs. The word can also be used in a more limited sense, to mean bivalves that burrow in sediment, as opposed to ones that attach themselves to the substrate (for example oysters and mussels), or ones that can swim and are migratory, like scallops. In addition "clam" can be used in an even more limited sense, to mean one or more species of commonly consumed marine bivalves, as in the phrase clam chowder, meaning shellfish soup usually made using the hard clam. Many edible bivalves have a roughly oval shape; however, the edible Pacific razor clam has an elongated, parallel-sided shell, whose shape suggests that of an old-fashioned straight razor.