Hydrozoa

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Hydrozoa (hydrozoans; from Ancient Greek ὕδωρ (húdōr) 'water' and ζώα (zóa) 'animals'), also called hydroids, are a taxonomic class of individually very small, predatory cnidarian 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, together with the true jellyfish, or scyphozoans, are members of the cnidarian subphylum Medusozoa. Some examples of hydrozoans are the freshwater jelly (Craspedacusta sowerbii), freshwater polyps (Hydra), Obelia, Portuguese man o' war (Physalia physalis), chondrophores (Porpitidae), and pink-hearted hydroids (Tubularia).

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