Bivalves

Click on photo to enlarge. Scale line in photo equals 1cm unless otherwise specified.
* Species which are commonly encountered on the beach.

Nisqually Reach, WA Thetis Island, BC, intertidal

Cryptomya californica (Conrad, 1837)
California Softshell-Clam
intertidal to 80m Peru to southern Alaska; Japan size to 37mm
This is occasionally found intertidally. It prefers a somewhat muddy location. The shell is thin and fragile. It exhibits a chondrophore like all Myidae. This is the spoon-shaped projection at the top of the left valve.

Semiahmoo Spit, WA Thetis Island, BC
showing siphon and part of foot, submerged in water

Mya arenaria Linnaeus, 1758
Eastern Softshell-Clam *
intertidal to 73m size to 170mm
southern California to northern Alaska; circumboreal, reaching south to Japan, Spain and North Carolina
This was introduced to California over 130 years ago and has naturalized itself all the way to Alaska. It is commonly found in both mud and sand. The shell shape can be somewhat variable but it is usually somewhat pointed at the front. The periostracum is thin and readily flakes off.

Mya truncata Linnaeus, 1758
Truncated Softshell-Clam
intertidal to 100m size to 85mm
northern Washington to northern Alaska; circumboreal and panarctic, reaching south to Japan, New England and Western Europe
This is rarely found intertidally in its southern range, but commonly found intertidally in Alaska. It prefers mud and sand. It can be distinguished from M. arenaria by its blunt posterior end and more of the periostracum remains adhered to the shell. Also, the siphon has a tough covering that can remain attached to the shell even after the animal has died and been eaten, as shown by the photo above.

Platyodon cancellatus (Conrad, 1837)
Boring Softshell-Clam
intertidal to 100m size to 76mm
northern Mexico to northern BC
This is occasionally found intertidally. It bores into hard-packed clay, mudstone or soft sandstone. The shell has a blunt posterior end and a sculpture of low, wavy commarginal ribs.

Family Myidae