The taxonomy of the polyclad flatworms is fairly well-known and some attention has been given to study of their physiology. Investigations of an ecological nature, however, are scarce; in fact, no ecological studies have been made on the Pacific Coast of North America. Else- where, Pearse and Wharton (1938) investigated the general ecology of Stylochus frontalis, associated with oysters on the coasts of Florida, and occasional notes have appeared, reporting on polyclads as predators on oysters and barnacles (Book, 1925: Wolke, 1954; Loosanoff, 1956: Skerman,1960)