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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