Portuguese man-of-war, (Physalia physalis), species of jellylike marine animals of the order Siphonophora (class Hydrozoa, phylum Cnidaria) noted for its colonial body, floating habits, and powerful stings.

Physalia physalis is a conspicuous, accessible and robust siphonophore as compared to other members of the order that are fragile and difficult to collect. It consists of numerous nematocysts that sting painfully, killing fishes and even humans.

The Atlantic Portuguese man o' war (Physalia physalis), also known as the man-of-war, or floating terror, is a marine hydrozoan of the family Physaliidae found in the Atlantic Ocean, as well as the Indian and Pacific Oceans. Its venomous tentacles deliver a painful sting, which on extremely rare occasions has been fatal to humans.

Physalia physalis is a species belonging to the family Physaliidae of the order Sihponophora. It is commonly called as Portuguese man o’ war or simply man-of-war. This species is a siphonophore and therefore it occurs in colonies just as other members of this group.

Physalia is a genus of the order Siphonophorae, colonies of four specialized polyps and medusoids that drift on the surface of the Atlantic, Indian and Pacific oceans.