[3] The exterior of the valves is covered in a shiny brown periostracum, hence one of its common names, "varnish clam".

[4] Right and left valve of the same specimen: These clams are found in the mid to high intertidal zone, buried in sand, gravel, or silt, from just below the surface to 20 centimetres (7.9 in) deep.

They have greater tolerance for salinity conditions than native clams and are sometimes found in brackish waters near freshwater seeps.

It is hypothesized that planktonic larvae were released by a ship disposing of ballast water she had pumped aboard in Asia.

A 2006 study of reproductive ecology and dispersal potential suggested that a "lengthy planktonic phase, combined with favourable oceanographic circulation patterns, has contributed to the rapid dispersal and geographic range expansion of the varnish clam in the Northeast Pacific.

[6] Where they find suitable habitat, these clams can reach densities of as high as 800 individuals per square meter.

This species also has the ability to gather material from the surrounding sand with its foot, sweeping detritus to its mouth.

These clams are preyed upon by raccoons, glaucous-winged gulls, Lewis' moonsnails, black oystercatchers, crows, and others.

[3]  Nuttallia obscurata is also eaten by Dungeness and red rock crabs, both of which appear to prefer it to native littleneck clams, because it is easier to eat.