The taxonomic group of hydroids that are not single animals, but colonies of animals. They may be either free swimming or floating, with or without a float. The genus of dominating medical importance is Physalia.
The taxonomic class including the plume-like hydroids, hard stinging “corals”, small jellyfish with bells (i.e. bell-shaped bodies), and members of the order Siphonophora which may be buoyed up by gaseous floats.... hydrozoa
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