The Portuguese man o' war isn't one animal — it's a colony of thousands as one

Despite looking and acting like a jellyfish, the Portuguese man o' war is a siphonophore: a colonial organism made of specialized, genetically identical individuals called zooids, each unable to survive alone, with different zooids handling floating, stinging, digesting or reproducing. Its venomous tentacles can trail over 30 meters and keep stinging long after the animal has washed ashore and died.

— Species account, Portuguese man o' war — Physalia physalis