Portuguese Man-of-war

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. It is often mistaken for a jellyfish. The Portuguese man-of-war’s prominent physical feature is its pneumatophore, a gas-filled bladder on its top that looks like the inflated sail of a ship and serves as both a float and a sail, allowing the animal to achieve maximum drift on the surface of the water.

The species is named for its resemblance to a class of warships that was developed in Portugal beginning in the 15th century with the caravel, a light agile sailing ship, called a man-o-war, that efficiently harnessed the wind. Physalia physalis is the only accepted species; however, some sources classify a regional form—the bluebottle, also called the Indo-Pacific man-of-war—that occurs in the Pacific and Indian oceans near Australia as a separate species called P. utriculus.