This sea star has five stout rays that range in length from 4 to 10 inches. The rays are arranged around an ill-defined central disk. While most of them are purple, they can be orange, orange-ochre, yellow, reddish, or brown. The aboral surface contains many small spines called ossicles that are arranged in a netlike or pentagonal pattern on the central disk. The Pisaster has tube feet that have suckers on their distal ends which allow them to attach to the rocky substrate and live in heavily wave-swept areas.