What type of colonial animal is a Portuguese man o' war?

A Portuguese man o' war is a siphonophore, a colonial hydrozoan made of specialized zooids. Although it resembles a jellyfish, it is not a single jellyfish individual.

Each zooid performs a particular role, such as floating, feeding, reproducing, or capturing prey. The colony functions as an integrated unit, with the different members depending on one another. Its gas-filled float, called a pneumatophore, keeps much of the colony at the sea surface.

Long fishing tentacles hang below the float and contain stinging cells that immobilize prey. These tentacles can extend many metres, and contact can cause painful stings in humans. Wind and currents move the colony because it cannot swim in the same way as a fish or actively propel itself like many jellyfish.

The name comes from the float's resemblance to the helmets associated with Portuguese soldiers in the sixteenth century. The animal is sometimes called a bluebottle in parts of the world, but that common name can also refer to related organisms, so the scientific classification is the clearest answer.