What are the Portuguese man o’ war found in the Caribbean and why are they dangerous?

At first glance, the Portuguese man o’ war (fragatas portuguesas in Spanish) can be striking and even beautiful to observe, but it’s best to keep a safe distance and never, ever, under any circumstances, touch any.

Their appearance is deceptive. The Physalia physalis is a marine hydrozoan of the family Physaliidae found in the Atlantic, Indian and Pacific Oceans. Its long tentacles deliver a painful sting, which is venomous and powerful enough to kill fish or, rarely, humans.
Despite its appearance, the Portuguese man o’ war is not a true jellyfish but a siphonophore, which is not actually a single multicellular organism (true jellyfish are single organisms), but a colonial organism made up of specialized individual animals (of the same species) called zooids or polyps.
How did they

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