- Hydrozoa, class Hydrozoa - coelenterates typically having alternation of generations; hydroid phase is usually colonial giving rise to the medusoid phase by budding: hydras and jellyfishes
--1 is a kind of class
--1 is a member of Cnidaria, phylum Cnidaria, Coelenterata, phylum Coelenterata
--1 has members:hydrozoan, hydroid; genus Hydra; Siphonophora, order Siphonophora; Sertularia, genus Sertularia