Clam

1. Any of various usually burrowing marine and freshwater bivalve mollusks of the class Pelecypoda, including members of the genera Venus and Mya, many of which are edible. In October 2007 an Arctica islandica clam, caught off the coast of Iceland, was discovered to be at least 405 years old.
2. The word "clam" has given rise to the metaphor "clam up", meaning to refuse to talk or answer, based on the clam behavior of quickly closing its shell when threatened. The suspect clammed up when confronted by the police.