Question: What is the  large marine bivalve mollusc species with the scientific name "Panopea generosa"?

Context paragraphs:
Solecurtus strigilatus: Solecurtus strigilatus, commonly known as the rosy razor clam, is a species of saltwater clam, a marine bivalve mollusc in the family Solecurtidae.  This mollusc is a suspension feeder and can burrow with great rapidity to escape predators.  It is an unusual bivalve in that its shell valves are too small to contain all the soft tissue, and the animal is unable to retreat into its shell.

Tresus capax: Tresus capax is a species of saltwater clam, marine bivalve mollusk, common name the fat gaper, in the family Mactridae.  It also shares the common name horse clam with "Tresus nuttallii" a species which is similar in morphology and lifestyle.  Both species are somewhat similar to the Geoduck ("Panopea generosa" which is in the family Hiatellidae), though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg).  The two species commonly known as horse clams inhabit the Pacific coast intertidal zones: the pacific gaper, "T. nuttallii", more abundant south to California; and the fat gaper, "T. capax", more abundant north to Alaska.  Both have oval and chalky-white or yellow shells with patches of brown periostracum (leather-like skin) on the shell.  These clams are also commonly called gapers because their shells are flared around the siphon and do not completely close, rather like geoduck clams.  Like geoducks, they are unable to completely retract the siphon within the shell, though less flagrantly as the siphon on "Tresus" species is not as large.

Lutraria lutraria: Lutraria lutraria is a species of large marine bivalve mollusc in the family Mactridae.  Its common names include the otter shell and the common otter shell.  It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand.

Panopea smithae: Panopea smithae is a species of large marine bivalve mollusc in the family Hiatellidae, found in the waters surrounding New Zealand.  Unlike its relative "Panopea zelandica", it lives in deeper waters, ranging from deep harbours to the outer continental shelf.

Panopea glycimeris: Panopea glycimeris is a species of large marine bivalve mollusc in the family Hiatellidae.

Zenatia acinaces: Zenatia acinaces is a species of moderately large marine bivalve mollusc in the family Mactridae.

Panopea abrupta: Panopea abrupta is an extinct species of large marine bivalve mollusc in the family Hiatellidae.  Between 1983 and 2010, this species of clam was confused with the Pacific Geoduck, "Panopea generosa", in the scientific literature.

Geoduck: 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".

Panopea zelandica: Panopea zelandica, commonly known as the Deepwater Clam or New Zealand geoduck (geoduck), is a large species of marine bivalve mollusc in the family Hiatellidae.  "Panopea zelandica" is also sometimes called a King Clam or a Gaper in reference to the shell not being closed at either end.

Crassula aequilatera: Crassula aequilatera, known as the triangle shell, is a surf clam, a moderately large marine bivalve mollusc in the family Mactridae.

Supporting paragraphs: Panopea abrupta Geoduck
Answer: Geoduck