The upper, aboral, surface is smooth and velvety, made more so by the absence of spines and a light layer of mucous.

This starfish can grow to about 30 centimetres (12 in) in diameter[3] and has a distinctive smell that resembles garlic and sulphur.

[4][5] The range of the leather star includes the western seaboard of North America from Cook Inlet, Alaska[2] to northern Mexico.

The worm also associates with various other marine invertebrates, but if separated from its host, will search out another member of the same species.

The worm may nip off the heads of small tube-dwelling polychaetes as the starfish moves around, but is not harmed by its host.