“Fat Gaper” (Tresus capax)
Also known as the horse clam (a name it shares with Tresus nuttallii as well) Tresus capax is a species of saltwater Mactrid clam that inhabits the Pacific coast of North America, ranging from California north to Alaska. Tresus capax typically inhabits intertidal areas and will bury itself in sand, mud, and gravel substrates. Like most bivalves T. capax is a filter feeder and will filter the water around itself for nutrients. T. capax is also known to hold a relationship with the small pea crab Pinnixa faba which will enter the bivalve through its large siphon and live inside its mantle cavity.
Image: Minette Layne