What is "siphonophora"

Siphonophora \Si`pho*noph"o*ra\, prop. n. pl. [NL., fr. Gr. ??? a siphon + fe`rein to bear.] (Zo["o]l.) An order of pelagic Hydrozoa including species which form complex free-swimming communities composed of numerous zooids of various kinds, some of which act as floats or as swimming organs, others as feeding or nutritive zooids, and others as reproductive zooids. See Illust. under Physallia, and Porpita.