What type of organism is a Portuguese man o' war?

The Portuguese man o' war is a siphonophore.

It is not a single animal in the usual sense but a colonial organism made of specialized individuals called zooids. These zooids are connected and cooperate as one functioning colony. A gas-filled float keeps the colony at the ocean surface, while long tentacles capture prey with stinging cells.

The name refers to the organism’s resemblance to the helmeted ships or soldiers associated with Portugal’s navy in earlier centuries. Its scientific name is Physalia physalis, and it drifts with winds and currents rather than swimming under its own power.

People often call it a jellyfish because it has tentacles and a painful sting, but jellyfish belong to a different group within Cnidaria. The Portuguese man o' war is a siphonophore, alongside related colonial hydrozoans. Its tentacles can extend many metres and may remain dangerous even after the colony has washed ashore.