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geoduck (gōō´ēdŭk´), common name of a Pacific clam, Panope generosa. The largest intertidal burrowing bivalve in the world, the geoduck may weigh up to 12 lb (5.4 kg). The shell is thin, lacks teeth, and may attain a length of 8 in. (20 cm). The valves, or two parts of the shell, are always open in the adult, because the body and siphons are too large to be retracted. Geoducks are found from British Columbia to S California, with the largest population in Puget Sound. They inhabit mud flats, burrowing to a depth of 3 or 4 ft (90–120 cm), where they live in semipermanent burrows. Although they are edible, they are not widely marketed due to their inaccessibility: They are exposed for only a few hours a month during minus tides, at which time they can be obtained with a shovel. Digging geoducks is considered a sport in Washington, where there is a limit of three per day. Geoducks are classified in the phylum Mollusca, class Pelecypoda or Bivalvia, order Eulamellibranchia, family Saxicavidae.