Found from Alaska to Cedros Island, Baja Calif, from the low intertidal zone to 216 meters depth. Up to 50 centimeters long. Mottled reddish brown, dark red, brown, or yellow in color (rarely white), with prominent, stiff, conical papillae sometimes tipped in red, and tube feet on its underside. Larger than P. parvimensis, with a more northerly distribution. Feeds on the organic detritus and small organisms in soft sediments. Eaten by the sunflower star Pycnopodia helianthoides and the seastar Solaster endeca. Escapes from these seastars by looping along the bottom like an oversized inchworm, or by flexing its body in a swimming manner. Eaten by humans and the sea otter. Reported to have single-cell ciliated organisms living in its respiratory trees inside the anus. A scale worm Arctonoe pulchra may be found on its body. Adults in Puget Sound eviscerate their internal organs in October and November, and then regenerate new sets of internal organs.
Sea cucumbers are soft-bodied wormlike echinoderms, having a body cylinder with a mouth at one end encircled by tentacles, and the anus at the other. They have the basic echinoderm radial symmetry, but no arms, and the echinoderm skeleton is reduced to small, scattered calcareous bonelike plates, and is usually flexible. Sea cucumbers have a water-vascular system, with or without tube feet, and respiratory trees inside the anus.