Pacific Geoduck

How to Distinguish from Similar Species: This is our largest local clam. Other members of family Hiatellidae are smaller and have gaping valves but a discontinuous pallial line. Gaper clams such as Tresus capax do not get as large and gape mainly at the posterior end. The Atlantic geoduck, P. bitruncata, does not live here and is smaller.

Geographical Range: Coast of Asia down to Japan; in North America from central Alaska to Newport Bay, CA; Mexico; Panama. In the Salish Sea area they are especially common in Hood Canal and Puget Sound. More common here than farther south.

Depth Range: Subtidal down to 100 m depth

This gigantic clam has fused siphons far too large to fit into the mantle cavity. The siphons can project up to a meter from the shell and cannot be retracted into the shell. The shell is dirty white to cream with a small amount of yellow periostracum. It has well-developed concentric lgrowth ines but no radial ribs. Each valve has one hinge tooth. The shell gapes widely on all sides except the hinge, and very widely on the posterior end. Unlike most members of its family, its pallial line is continuous and wide. The long siphons ares light brown with darker brown on the end. There are no thick pads on the end of the siphons. Shell is quadrate, more rounded on the anterior than the posterior end, up to 23 cm long, animal to 9 kg. The single hinge teeth of the two valves do not match well.

Biology/Natural History: This animal is said to be the largest burrowing clam. It does not mature until age 3-4. Spawning is in the spring. Young clams have spiny shells and often settle on the tubes of polychaetes, where they attach for a time by byssal threads before dropping off and digging into the sediment. It is very long-lived. The copepod Herrmanella panopeae has sometimes been found as a symbiont inside the shell. Adults of this species are poor diggers and do not seem to be able to dig themselves back into the mud if removed. Ricketts et al. state that the shell is lightweight but the shell of the specimen above is probably 1/2 cm thick.

Burrows very deeply in soft bottoms in quiet waters.