Twenty-five marine hydroid species were encountered in studies on Hueneme Shelf. Fourteen species appear to occur primarily in areas of soft substrates. These species exhibited distinct patterns in depth distribution and specific substrate preference. Clytia bakeri and Phialella ?rugosa characterized the shallow region of the study area (3 to 11 m), Tubularia sp. A, Plumularia alicia, Hydrallmania distans, Aglaophenia dispar, Clytia universitatis, and Lovenella nodosa characterized the mid-depths (11 to 33 m), and Plumularia mobilis, Monobrachium parasitum, Thuiaria ?alba, Euphysa sp., Corymorpha palma, and Aglaophenia lophocarpa characterized the deeper region (24 to 60 m). These patterns were stable over several years. Factors probably operative in these distribution patterns include sediment stability, availability of substrates, and food. Favored substrates were polychaete worm tubes, shells, and shell debris. <br />These observations constitute range extensions for eight of the species. Two species are probably undescribed. Natural history information is presented on all species.