Thirteen species of Pilargidae (Annelida: Polychaeta) from the subtidal and intertidal Pacific Coast of Costa Rica are reported. A new species, Sigambra vargasi n. sp., is described and an as yet undescribed species, Sigambra sp. A, is also reported. The occurrence of Sigambra tentaculata (Treadwell), Loandalia riojai Salazar-Vallejo, Pilargis berkeleyi Monro, Ancistrosullis hamata Hartman and Ancistrosyllis jonesei Pettibone are range extensions for these species. The occurrence of Sigambra pellibaneae Hartmann-Schroder, Pirandalia tricuspis (Müller), Cubira incerta Webster, Ancistrosyllis papillosa Jones and Ancistrosyllis hartmanae Pettibone are new re cords of these species for the eastern Pacific Ocean. Synelmis cf. albini (Langerhans) is also reported. A taxonomic key to these species is included.
Keywords: Polychaeta, Pilargidae, Pacific coast, Costa Rica