Cothurnia limnoriae is a commensal suspension-feeding attached ciliate of wood-boring isopods (gribbles, Limnoria spp.) on the Pacific coast. The gribbles Limnoria quadripuncata and L. tripunctata were introduced to California in the 19th century. This ciliate was first reported by Koifoid and Miller from San Francisco Bay in 1927, but may have been present with the first recorded Limnoria in 1870. Cothurnia limnoriae feeds on bacteria and other suspended particles.