True jellyfish (like moon jellies, box jellyfish)are a single organism, just like you or me. Theres a single genome and one body.

Portuguese man o’ war is not a single organism at all but a siphonophore, a colony of many genetically identical but specialized individual organisms called zooids, all fused together and functionally dependent on each other.

Whats the difference between a siphonophore and a single organism? Aren't all the organs of an organism genetically identical, specialized, fused together, and functionally dependent on each other?