Purple Mahogany Clam

The valves are thin, relatively shallow, and almost oval in shape. They can reach 6.4 centimetres (2.5 in) long. Individuals can achieve a maximum weight of 45 grams (1.6 oz). The exterior of the valves is covered in a shiny brown periostracum, hence one of its common names, "varnish clam". The periostracum is often worn away at the umbo. There are concentric rings on the outside of the valves which can be observed where the periostracum has been removed. The interior of the valves is deep purple to almost white in some individuals. The prominent hinge ligament is external to the valves. Nuttallia obscurata has a large white, muscular foot that it uses to dig in the sand and for propulsion. The animal has two long, white, separate siphons.

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. The species is native to Japan, Korea, and China. It has been naturalized in British Columbia, Washington and Oregon. Its range includes the coast of Vancouver Island, the Strait of Georgia, Puget Sound, and south along the coast to Coos Bay. It is considered an invasive species in North America.

Nuttallia obscurata can live at least six years. They begin life as free-swimming plankton. This planktonic stage can last from 3 to 8 weeks before they settle to the bottom as recognizable clams. They become reproductively mature at one year old. This species is protandrous, where the young forms are male and then become female later in life. In each population, there are males and females in approximately equal numbers, and 4-5% of the population is hermaphroditic. In some populations, the sex ratio skews towards males for reasons that are not known. Females have been observed to produce between 40,000 and 6,000,000 eggs during the summer breeding season. These oocytes are 55 micrometres (0.0022 in) in diameter. Fertilization takes place by broadcast spawning.

British Columbia, Washington, and Oregon, all have recreational fisheries for Nuttallia obscurata.

No large-scale commercial fishery exists for this species, although small commercial landings are ongoing in both British Columbia and Washington. Marketing efforts have produced another common name, savory clam, for this species.

Nuttallia obscurata is subject to paralytic shellfish poisoning. They retain biotoxins longer than other clams, so care should be taken when harvesting them.