The Entocommensal Ciliate Fauna of the Pink Sea Urchin, Allocentrotus fragilis

Although there are numerous records of ciliates inhabiting the digestive tracts of other strongylocentrotid echinoids, no information concerning those resident in Allocentrotus fragilis (Jackson, 1912) Mortensen, 1942, has been published. In February 1960, the senior author's attention was directed to the presence of a faunule of ciliates inhabiting this species by Dr. A. R. Moore, Hopkins Marine Station of Stanford University, Pacific Grove, California. During the summer of 1960 the gut contents of several specimens of A. fragilis from widely separated localities along the Pacific Coast were examined for ciliate infestations.