Gaper or Horse Clam    Tresus capax


The Gaper clam weighs in from one to four pounds and the shell can be up to 8 inches long.  The Gaper clam burrows as it grows reaching the surface with long siphons. However the Gaper only goes around 25 inches into the sediment.  


At the surface the tips of the siphons can be used to distinguish between the Gaper clam and the Geoduck clam, the tip of the geoduck is fleshy while the Gaper has hard valves on each side of the siphon opening.  


There are also two species of Gaper in Puget Sound.  Capax or fat gaper is more common, however a southern cousin, Tresus nuttalli or Pacific Gaper, can be present in the same bed.  The Fat Gaper has a more oval shell and soft siphonal valves while the shell of the Pacific Gaper is oblong with hard valves. Both species harbor one of several pea crab species that live permanently in their mantle cavity feeding off plankton brought in by the clam.  


These clams are attacked by crabs, moon snails and the giant pink sea star.