A class of coelenterates which includes hydras and Portuguese men-of-war. Many of them are colonial and some kinds have both polypoid and medusoid phases.
- ‘The groups Hydrozoa, Scyphozoa and Cubozoa all are generally characterized as having polyps and medusae (although minor lineages have lost medusae and in some cases polyps).’
- ‘Another feature that is quite common in Hydrozoa but not typical of Scyphozoa is colonial organization.’
- ‘However, Hydra is not typical of the Hydrozoa as a whole.’
- ‘Traditional systematics divides the Hydrozoa into five orders.’
- ‘While the Cubozoa always have polyp and medusa stages, either one can be reduced in the Hydrozoa and Scyphozoa.’
Modern Latin (plural), from hydro-‘water’ + Greek zōion ‘animal’.
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