It's actually a clam

• Large clam
• Has siphons that can extend to several feet and cannot be withdrawn into the shell
• A large edible clam found burrowing deeply in sandy mud along the Pacific coast of North America
• Weighs up to six pounds

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Geoduck \Ge"o*duck\, n. [American Indian name.] (Zo["o]l.) A gigantic clam ( Glycimeris generosa ) of the Pacific coast of North America, highly valued as an article of food.

WordNet Word definitions in WordNet
n. 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the Pacific coast of North America; weighs up to six pounds; has siphons that can extend to several feet and cannot be withdrawn into the shell

Wiktionary Word definitions in Wiktionary
n. A species of large saltwater clam, native to the North American Pacific Northwest, Washington to Alaska, known as (taxlink Panopea abrupta species noshow=1) or (taxlink Panope generosa species noshow=1), in the family Hiatellidae.

Wikipedia Word definitions in Wikipedia
The Pacific geoduck , scientific name Panopea generosa , is a species of very large, edible saltwater clam in the family Hiatellidae . The common name is derived from a Lushootseed ( Nisqually ) word gʷídəq . The geoduck is native to the west coast of North ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
edible Pacific clam, 1883, perhaps from some American Indian word.