cnidarian, coelenterate - radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms

planula - the flat ciliated free-swimming larva of hydrozoan coelenterates

class Hydrozoa, Hydrozoa - coelenterates typically having alternation of generations; hydroid phase is usually colonial giving rise to the medusoid phase by budding: hydras and jellyfishes

hydra - small tubular solitary freshwater hydrozoan polyp

siphonophore - a floating or swimming oceanic colony of polyps often transparent or showily colored

sertularian - feathery colony of long-branched stems bearing stalkless paired polyps