What does hydrozoa mean?
Hydrozoa is a taxonomic class within the phylum Cnidaria, the group that also includes jellyfish, sea anemones, and corals. Its members are commonly called hydrozoans and include hydras, many small jellyfish, and numerous colonial organisms. A characteristic life cycle alternates between an attached, usually polyp-like stage and a free-swimming, medusa-like stage, although some species omit one stage or remain in a predominantly polyp form. Hydrozoan colonies may produce specialized feeding, reproductive, and defensive individuals that remain connected. The class is predominantly marine, but hydras and a few other members live in fresh water. The term is primarily used in zoological and ecological classification, where it distinguishes this evolutionary group from other cnidarians.
nounHydrozoa is a class of mostly marine cnidarians that includes hydras, many jellyfish, and coral polyps. Members may have a life cycle involving a free-swimming medusa stage, a attached polyp stage, or both.
- Hydrozoa denotes the taxonomic class containing hydras, most hydrozoan jellyfish, and certain coral-like colonial animals.
"The class Hydrozoa includes species that alternate between a conspicuous medusa and a sessile polyp."
"Researchers found an unusual colonial species within Hydrozoa along the continental shelf."
"The hydra is a small freshwater member of the class Hydrozoa."
In modern taxonomic prose, individual members of the class are commonly called hydrozoans; Hydrozoa normally names the class as a whole.
"Several colonial hydrozoans were observed growing on the reef."
Hydrozoans can live as both stationary polyps and swimming jellyfish, with some species carrying out two very different lives in a single life cycle.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hydrozoa come from?
Hydrozoa combines New Latin hydro-, from Greek hydro meaning “water,” with New Latin -zoa, from Greek zōion meaning “animal.” The name reflects the class's close association with water and its inclusion of many animal forms. Its cognate hydrozoan is used for individual members of the class, while the taxonomic name Hydrozoa is conventionally capitalized.
Related word forms
How hydrozoa is actually used
In formal biological taxonomy, the class name is normally capitalized as Hydrozoa. The adjective hydrozoan describes organisms belonging to the class.