Large specimens exceeding 40 cm in length and weighing several kilograms. Mature forms reddish, brownish, and or greenish, overlaid with a network of dark lines arising from scattered roundspots. Young specimens usually reddish, marked with banding on upper, inner surfaces. The shell is internal.

Among seaweed, sometimes in kelp canopy.

Low intertidal to over 18 m; Humboldt Bay, California to Gulf of California, Mexico.