ˌhīdrəˈzōə noun plural
Usage: capitalized
Etymology: New Latin, from hydr- (hydroid) + -zoa
: a class of coelenterates that includes various simple and compound polyps and jellyfishes having no stomodaeum or gastric tentacles and differing widely in appearance, structure, and habits, some being attached polyps which have no free-swimming stage, others being always free-swimming and the majority having an alternation of a free-swimming sexual generation with an attached asexual generation — see hydroida , milleporina , siphonophora , stylasterina , trachylina