cnidarian,
coelenterate radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms
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
planula the flat ciliated free-swimming larva of hydrozoan coelenterates
hydra small tubular solitary freshwater hydrozoan polyp
siphonophore a floating or swimming oceanic colony of polyps often transparent or showily colored
