PhysaliaPhy*sa"li*a\, n. [NL., fr. Gr. ? a bladder, fr. ? a bellows.] (Zo["o]l.) A genus of large oceanic Siphonophora which includes the Portuguese man-of-war. Note: It has a large air sac, or float, with a sail-like crest on its upper side. Numerous zooids of different kinds are attached to the under side of the float. Some of the zooids have very long tentacles; some have a mouth and digest food; others produce gonophores. The American species (Physalia arethusa) is brilliantly colored, the float being pink or purple, and bright blue; the zooids blue. It is noted for its virulent stinging powers, as well as for its beautiful colors, graceful motions, and its ability to sail to windward.