The general colour is brown with the inside of the shell being glossy white with a purple patch at the hinge and a large, central adductor muscle scar.

[3][4] Crassadoma gigantea is found on the Pacific Coast of North America, from British Columbia south to Baja California and Mexico.

Its favoured habitats include inside crevices and under boulders, or cemented to rock surfaces, corals or man-made structures such as harbour pilings.

[6] Crassadoma gigantea is cryptic and difficult to detect because of the sponges, sea anemones, hydroids, barnacles, bryozoans, worms and algae which tend to grow on the shell.

[5] It has been found experimentally that rock scallops grow at a faster rate when living in deep rather than shallow water, perhaps because they are then less hindered by these fouling organisms.

Rock scallops can live for at least 20 years [4] but by about halfway through their adult life, growth slows, and energy is concentrated into gamete production.