On the oral (lower or ventral) surface a long ambulacral groove stretches from the central mouth to the tip of each arm with four rows of tube feet and clumps of pedicellariae and spines on either side.

Its range extends from Pribilof Islands, Alaska southwards to Monterey Bay, California but it is rarely seen south of Puget Sound.

[2] In bays and other sheltered locations it largely replaces the other common species of the area, the purple sea star (Pisaster ochraceus).

With its tube feet it can exert a powerful traction on the two valves of a mollusc shell, pulling them sufficiently far apart to insert part of its stomach through the gap.

[5] Petroleum hydrocarbons, such as those released as a result of the Exxon Valdez spillage, have a greater effect on the feeding and growth of the mottled star than on one of its main prey species, the mussel Mytilus edulis.

Researchers surmised that pollution of the marine environment with oil might result in the domination of the mussel in the low intertidal zone of the region.

[8][9] Juvenile Alaskan king crabs (Paralithodes camtschaticus) have been observed living as commensals on the surface of the mottled star, sheltering between its arms.

[6] It is also preyed on by gulls in the intertidal zone and by the morning sunstar (Solaster dawsoni) and the sunflower seastar (Pycnopodia helianthoides).