Prey includes mainly bivalves, including Clinocardium
cockles, butter clams, littleneck clams, and geoduck clams; but also snails, sand dollars, barnacles, and tubicolous polychaetes; may scavenge dead fish and squid. The purple olive snail Olivella biplicata
shows a strong escape response to this species (it buries itself), as does the sand dollar Dendraster excentricus
. Known to feed on small Dungeness crabs in California. May fight with Pycnopodia helianthoides
over food if they both encounter it. The tube feet next to the mouth can be extended many centimeters (up to the seastar's redius) to pull up bivalves from the sediment. May also dig in sediment after prey, which may take several days. The stomach may be everted up to 8 cm to digest prey in the shell. Spawns in spring and summer in Washington. A small snail, Balcis rutila
, may be embedded in the body wall. A smaller subspecies (P. brevispinus
) lives in Tomales Bay in eelgrass, and has fewer spines.