geoduck a large edible clam found burrowing deeply in sandy mud along the Pacific coast of North America; weighs up to six pounds; has siphons that can extend to several feet and cannot be withdrawn into the shell
clam -
To be moist or glutinous; to stick; to adhere.
Wikipedia
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves. 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 which burrow in sediment, as opposed to ones which attach themselves to the substrate, or ones which can swim and are migratory, like scallops.
OmegaWiki Dictionary
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clam A marine or freshwater mollusks belonging to the class Bivalvia, whose body is protected by two symmetrical shells.