I have a definite love-hate relationship with Portuguese Man o’ War. They are beautiful, delicate, exotic and extremely painful. I still remember being stung twice as a child over a half century ago. What I only came to understand recently is that Portuguese Man o’ War are really strange. Portuguese Man o’ War are not jellyfish. They are a members of the very weird siphonophore class of marine animals that does not quite manage to fit into the scientific categories for either individual animals or a colony of animals living together, like, for example, coral.
Portuguese Man o ‘War and other siphonophores are made up of zooids. All colonial animals are made up of zoids, but what makes siphonophores so different is that siphonophore zooids are highly specialized. For example, the flotation bag of the Portuguese Man o’ War, termed the pneumatophore, is independent of the dactylozooid which handles defense, as well as the gonozooid which deals with reproduction, and gastrozooid, the nasty tentacles, which handles feeding. Each specialized zooid works collectively with the other specialized zooids, yet are not controlled by a brain.
Here is a video from SciShow which describes this weirdness in slightly more detail. A recent article in The Atlantic takes a look at a distant cousin of the Portuguese Man o’ War, the Nanomia bijuga.