The world's largest intertidal clam, the geoduck has made its home along the western Washington coast for some 25 million years. The word geoduck (also spelt "gweduck") is derived from the Lushootseed (Puget Salish) word "gwídəq" meaning "dig deep." This is an appropriate name, considering that the geoduck is probably the deepest-living clam in the world. Its scientific name, Panopea, comes from the name of a sea nymph in Greek mythology.
Panopea first appeared in the fossil record in the late Cretaceous, about 80 million years ago. Panopea snohomishensis is the first geoduck to appear in western Washington, aproximately 25 million years ago, and its fossils are found in rock outcrops on Bainbridge Island, Seattle, Bellevue, and a few localities along the Snohomish River. Panopea ramonensis is found in the 20-million-year-old Clallam Formation at Clallam Bay. Fossil and living geoducks occur all around the north Pacific Rim from California through the Aleutians to Japan and South Korea.
The living geoduck is one of the largest clams in the world. Geoducks can grow to over 5 kilograms with occasional specimens weighing in at 10 kilograms! Growth rings in geoduck shells (or valves) show ages to 140 years and older, making this clam one of the longest-living marine animals on record.
Shells of young geoducks grow approximately 2 cm per year in length, but after four years their growth rate slows. Young geoducks dig down into the sand; once they get about 1 meter below the surface they stop digging; the digging foot is reabsorbed, and the geoduck loses the ability to reposition itself. Geoducks are filter-feeders, like most other clams: they draw water in through one siphon, pass it over their gills to extract oxygen, and expel it out the other siphon. At the same time, mucus on the gills grasp phytoplankton, which are then passed to the mouth.
Geoducks can be found from the intertidal zone to depths of more than 120 meters. Geoducks are a highly prized delicacy. On the Olympic Peninsula the geoduck is an important species for sports and recreational fisheries.