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Any of various cnidarians of the class Hydrozoa, including the hydras, hydroids, and siphonophores, which exhibit alternation of generations between the polyp and medusa stage or exist in only one or the other stage.

[From New Latin Hydrozōa, class name : Hydra, type genus; see hydra + -zōa, pl. of -zōon, -zoon.]

hy′dro·zo′an adj.


(Animals) any colonial or solitary coelenterate of the class Hydrozoa, which includes the hydra, Portuguese man-of-war, and the sertularians
(Animals) of, relating to, or belonging to the Hydrozoa


(ˌhaɪ drəˈzoʊ ən)

1. any freshwater or marine cnidarian of the classHydrozoa, including attached and free-swimming, often colonial, forms in which the medusa stage is reduced or lacking.
2. belonging or pertaining to the hydrozoans.
[1875–80; < New Latin Hydrozo(a) (see hydro-1, -zoa) + -an1]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.hydrozoan - colonial coelenterates having the polyp phase dominanthydrozoan - colonial coelenterates having the polyp phase dominant
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
References in periodicals archive ?
This corresponds to ~9% (26 of 295 species recorded) and less than 1% (26 of 3,428 species recorded) of the hydrozoan species recorded for the Argentinean Patagonia and worldwide, respectively (Oliveira et al, 2016; Schuchert, 2016), showing that the knowledge on the biodiversity of hydroids at intertidal habitats of Argentinean Patagonia is still scarce.
Indeed, several deep-sea hydrozoan jellyfish appear to have distributions spanning ocean basins (Collins et al.
But this hydrozoan, common in the western Mediterranean and Adriatic seas, is something of a cheat.
The specimens were identified as the crawling medusa, Eleutheria dichotoma, which is one of a small group of hydrozoan medusae that crawls on algae rather than swimming in the plankton.
The endozoic association and its diminutive tetrasporic filaments likely represent an advantageous adaptation to low incident light, which is further reduced in quality and quantity by the hydrozoan exosarc cover.
The discovery of green fluorescent protein in a hydrozoan jellyfish in the 1960s has provided a revolutionary tool for modern biologists, transforming our study of everything from the AIDS virus to the workings of the brain," Gruber said.
and others, Patterns in marine hydrozoan richness and biogeography around southern Africa: implications of life cycle strategy.
For example, throughout earth history, genuine scyphozoan, hydrozoan, or cubozoan medusae are only known from [less than or equal to] 10 deposits, all of which are significant or potential Konservatlagerstatten (Young and Hagadorn 2010).
The 4-5mm diameter creature, technically known as a hydrozoan, is the only known animal that is capable of reverting to its juvenile polyp state.
The freshwater jellyfish (Craspedacusta sowerbii) a hydrozoan with a complex lifecycle and a cosmopolitan distribution.
The team studied the largest-known population of black corals in the world, along with other unique coral colonies in the area, including red hydrozoan corals, solitary stony corals and various gorgonian sea fans.
We studied the swimming behavior of two species of gelatinous zooplankton, a comb jelly Mnemiopsis mccradyi (Phylum Ctenophora) and a hydrozoan jellyfish medusa Nemopsis bachei (Phylum Cnidaria), under the altered gravity conditions generated aboard NASA's KC-135 aircraft.