This important clam is not a native of North America, but was accidentally introduced to Washington State in oyster seed shipments from Japan. The animal quickly acclimated to our waters and is now found from British Columbia to northern California. They are similar in size and appearance to littlenecks; however, they are oblong in shape, being more long than high compared to littlenecks. The internal surface of the shells near the siphon end is normally stained a deep purple color or yellow. The shells completely close. Their siphons are short so they are buried to only about 4" fairly high in the intertidal zone. They inhabit a variety of substrates, from gravel to mud to sand, above the half-tide level, which is higher than the zone where butter and littleneck clams are found. The black siphon tips on Manilas are split. The inside edge of their shell is smooth to the touch. In Puget Sound, they are especially abundant in small outlets and lagoons. Growth is quite rapid with the clams reaching marketable size in two years.
This species has become a welcome addition to Washington's list of clams and is taken commercially by hand diggers and by sport diggers with shovels, forks and rakes. It is a shallow burrower with many found within the first two inches of substrate, and for this reason are easily harvested by hand-digging. Manilas account for 50 per cent of the annual commercial landings of hard-shell clams in Washington.
This clam, like the native littleneck, is normally prepared by steaming. They are summer spawners.