Macoma nasuta (Conrad 1837)

Buried in mud flats; also found in gravel, sand, or muddy clay

Geographical Range: Kodiak Island, Alaska to Cabo San Lucas, Baja California, Mexico

Depth Range: Low intertidal to 50 m

Like all members of family Tellinidae, this clam has a rounded shell with neither valve very flat nor very inflated, and the anterior and posterior ends are shaped differently. There are two adductor muscle scars of similar size on each valve. The umbones are near the middle of the dorsal side. It has no radial ribs. The hinge has a true hinge plate with two cardinal teeth on both valves. The hinge ligament is mostly external. The valves have a pallial sinus and a continuous pallial line. The valves gape only slightly, if at all, at the posterior end. The siphons are long and separate. Macoma nasuta has a long hinge ligament, no lateral teeth on its hinge plate, is less than twice as long as high, and the posterior end of both valves is bent to the right. The pallial sinuses are large, extend to beneath the anterior adductor muscle scars, and are very close to the pallial line ventral to them. Length to 11 cm but usually not more than 6 cm. Shells are chalky white and usually unstained, with some grayish-brown periostracum.

How to Distinguish from Similar Species: This is the only clam in this area that has the posterior ends of the valves bent strongly to the right. Tellina bodegensis, a much less common relative, may also be bent slightly to the right.

Biology/Natural History: This common clam lies on its left side instead of vertically, at a depth of 10-20 cm. It rocks back and forth while digging. The siphons extend out the right side and up to the surface, which are well accomodated by the twist to the right of the shell. The siphons are used to suck debris from the surface of the sediment like a vacuum cleaner. The clams digest mainly diatoms and some flagellates from the sediments. They ingest large quantities of sediment but reject 97% of it, producing copious pseudofeces. Hinton says the clam moves to another location when the sediment in an area has been thoroughly picked over. Predators include the moon snail Polinices lewisii. The clam was an important food of the coastal Indian tribes and to Chinese immigrants in San Francisco but is little used commercially today because of the debris that is usually in the gut. This species is very hardy and can be found in areas that have very poor circulation, and can live in very soft, silty mud. The pea crab Pinnixa littoralis or P. faba may live in the mantle cavity, as may the Nemertean worm Malacobdella grossa. The species spawns in early summer in Oregon.