Horse clams have chalky-white shells with yellow-brown skin-like patches. The horse clam is the only Washington clam whose siphon is tipped with leathery flaps, often with algae or barnacles attached. The siphon cannot be completely withdrawn into the shell.  The shell can reach a length of eight inches.  Horse clams are found in the lower intertidal areas of sand and gravel beaches buried one to three feet.

Butter clams usually have chalky-white shells with concentric rings.  They lack the radiating ridges found on the littleneck clam shells.  The siphon, or neck, can retract completely into the shell. They can grow to five inches in length and are common in the middle to lower intertidal areas.  The butter clam is found in the sandy/gravelly mud at depths between eight to 12 inches. 

Softshell clams have chalky white, fragile shells that are rounded at the foot end and tapered at the siphon end. The siphon cannot be completely withdrawn into the shell.  They are often mistaken for small horse clams. Softshell clams average four to six inches in length, and they are found in mud/sand beaches near the mouths of rivers, buried to a depth of eight to 14 inches.

Cockles are easily recognized by their prominent, evenly spaced, radiating ridges fanning out from the hinge area to the shell margin.  They have mottled, light brown shells and can grow to five inches.  Cockles are found intertidally near on the surface of sand/gravel beaches throughout Puget Sound.

Manila clams, also called Japanese littleneck clams, have oblong, slightly colored and patterned shells with purple staining inside. The shell, like the native littleneck clam has concentric rings and radiating ridges. They can grow up to three inches in length and are found higher in the intertidal area than the native littleneck clam. Manila clams are found on gravel/sand beaches, three to six inches below the surface.

Native littleneck clams have chalky white shells with well-defined circular rings and radiating ridges.  They can grow up to three inches in length and are often referred to as steamers.  Native littleneck clams are rounder than Manila clams and have no purple coloration on the inside of the shell. They are found on gravel/sand beaches in the lower half of the intertidal area and buried to a depth of six inches.  

Geoducks (Goo-ee-duck) are the world's largest burrowing clam and can reach an age of 140 to 160 years. Geoduck shells are chalky-white and may reach nine inches in length, but do not completely close. Their long siphon lacks the leather-like flaps of the horse clam. Geoducks are found on sand/gravel to mud/sand beaches, buried two to three feet deep. While they are less common intertidally, they are abundant subtidally.