What animal group does the Portuguese man o' war belong to?

The Portuguese man o’ war belongs to the siphonophores, a group of colonial hydrozoans.

It may look like a jellyfish, but the Portuguese man o’ war is not a true jellyfish. Its body is a colony of specialized zooids: genetically identical units that perform different tasks, including floating, feeding, reproduction and prey capture. Together they function as one integrated organism.

The familiar blue or purple float is a gas-filled structure called a pneumatophore. It keeps the colony at the ocean surface, where wind and currents move it. Long fishing structures hang beneath the float and carry venomous stinging cells called cnidocytes, which immobilize prey and can inflict painful injuries on people.

Siphonophores are cnidarians, the broader animal group that also includes jellyfish, sea anemones and corals. That relationship explains the visual confusion, but their colonial construction sets them apart. Carl Linnaeus described the Portuguese man o’ war in 1758, and its scientific classification has continued to receive study as researchers investigate variation within the genus Physalia.