Horse Clam
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Scientific Name Tresus nuttallii
Conservation Status Least Concern
Family Bivalve
Habitat PNW Shorelines
Food Plankton

The horse clam (Tresus nuttallii and T. capax) are related to the Geoduck, though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg). Two similar species of horse clams inhabit the Pacific coast intertidal zones: the pacific gaper, Tresus 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. Horse clams are called gapers because their shells are flared around the siphon and do not completely close, rather like geoducks. Like geoducks, they are unable to completely retract the siphon within the shell, though less flagrantly.

Their habitat is the lower intertidal zones on out to waters as deep as 50–60 feet (13-15 m). They prefer sand, mud, and gravel substrates, normally burying themselves 12–16 inches (30–41 cm), so they are much easier to dig than geoducks.

The meat is good and makes excllent chowder. They tend to be ignored by sport diggers in Washington but not in Oregon.

For resource sustainablitily, the Washington State Department of Fish and Wildlife sets size and bag limits for clams.