Hydrozoa

Hydrozoa (hydrozoans; from Ancient Greek ('''') 'water' and ('''') 'animals') is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater habitats. Hydrozoans are related to jellyfish and corals, which also belong to the phylum Cnidaria.

OverviewAI-generated

Hydrozoa is a class within the phylum Cnidaria of the kingdom Animalia. The taxon was described by Owen in 1843 and is currently accepted. Members of this group are commonly referred to as hydroids. The class originated approximately 575 million years ago.

Hydrozoa inhabit marine, brackish, and freshwater environments. Records of the class are held by institutions including YPM, USNM, FMNH, and UF, with occurrences documented in the United States, Sweden, and Canada. The subject is referenced by 1,043 other encyclopedia articles.

Synthesized by Vinony from 25 facts across 7 sources: Wikidata, GBIF, PubMed, Gbif Occ, WoRMS, iDigBio, Vinony graph. Generated from structured data (not the Wikipedia text) and checked against those facts — may still contain errors.

Species

hydroids

Hydrozoa

CLASS

KingdomAnimalia
PhylumCnidaria
ClassHydrozoa

Habitatmarine, brackish, freshwater

Observations recorded1,265,515

via GBIF

Museum specimens

Specimen records: 11,493
With media: 955
Collections: YPM, USNM, FMNH, UF
Recorded in: United States, Sweden, Canada

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Research

2,537 papers

Hydroids (Cnidaria, Hydrozoa) from Mauritanian Coral Mounds.Zootaxa · 2020Gil M, Ramil F, AgÍs JADOI: 10.11646/zootaxa.4878.3.2
Genome assembly of Bougainvillia cf. muscus (Cnidaria: Hydrozoa).G3 (Bethesda, Md.) · 2025Macias-Muñoz A, Varney R, Katcher E et al.DOI: 10.1093/g3journal/jkaf110
Hydrozoa metamorphosis and pattern formation.ReviewCurrent topics in developmental biology · 1998Berking SDOI: 10.1016/s0070-2153(08)60245-8
Extraction, purification and properties of aequorin, a bioluminescent protein from the luminous hydromedusan, Aequorea.Journal of cellular and comparative physiology · 1962SHIMOMURA O, JOHNSON FH, SAIGA YDOI: 10.1002/jcp.1030590302
Hydroids (Cnidaria, Hydrozoa) from Guinea Bissau.Zootaxa · 2025Gil M, Ramil FDOI: 10.11646/zootaxa.5577.1.1
Transcriptome Characterization of Reverse Development in Turritopsis dohrnii (Hydrozoa, Cnidaria).G3 (Bethesda, Md.) · 2019Matsumoto Y, Piraino S, Miglietta MPDOI: 10.1534/g3.119.400487
Global diversity and review of Siphonophorae (Cnidaria: Hydrozoa).ReviewPloS one · 2014Mapstone GMDOI: 10.1371/journal.pone.0087737
Global diversity of the Stylasteridae (Cnidaria: Hydrozoa: Athecatae).ReviewPloS one · 2011Cairns SDDOI: 10.1371/journal.pone.0021670

via PubMed

~11 min read

Encyclopedic overview

8 sections

Contents

Anatomy
Polyps
Medusae
Life cycle
Systematics and evolution
Other classifications
References
External links

Some examples of hydrozoans are the freshwater jelly (Craspedacusta sowerbyi), freshwater polyps (Hydra), Obelia, Portuguese man o' war (Physalia physalis), chondrophores (Porpitidae), and pink-hearted hydroids (Tubularia).

Excerpted from Wikipedia’s “Hydrozoa” article, available under the CC BY-SA 4.0 licence.