The Pacific geoduck (ˈɡuːiˌdʌk ; Panopea generosa) is a species of very large saltwater clam in the family Hiatellidae. The common name is derived from the Lushootseed(Nisqually) name, gwidəq.
The geoduck is native to the coastal waters of the eastern North Pacific Ocean from Alaska to Baja California. The shell of the clam ranges from to over in length, but the extremely long siphons make the clam itself much longer than this: the "neck" or siphons alone can be in length. The geoduck is the largest burrowing clam in the world. It is also one of the longest-living animals of any type, with a typical lifespan of 140 years; the oldest has been recorded at 179 years old. The precise longevity of geoducks can be determined from annual rings deposited in the shell which can be assigned to calendar years of formation through crossdating. These annual rings also serve as an archive of past marine variability.
The name Geoduck is derived from the Lushootseed (Nisqually) name for the animal, gwidəq. The etymology of gwidəq is disputed. The lexical suffix =əq means "many" in Lushootseed. The Oxford English Dictionary claims it is composed of a root word of unknown meaning and =əq instead meaning "genitals" (referring to the shape of the clam), while other researchers claim it is a phrase meaning "dig deep".
It is sometimes known as a mud duck, king clam or, when translated literally from Chinese, an elephant-trunk clam (). A group of geoducks is called a "bag".
Between 1983 and 2010, the scientific name of this clam was confused with that of an extinct clam, Panopea abrupta (Conrad, 1849), in scientific literature.
Native to the west coast of Canada and the northwest coast of the United States (primarily Washington and British Columbia), these marine bivalve mollusks are the largest burrowing clams in the world, weighing in at an average of at maturity, but specimens weighing over and as much as in length are not unheard of.
A related species, Panopea zelandica, is found in New Zealand and has been harvested commercially since 1989.