Physalia physalis, the Portuguese man o' war (family Physaliidae, order Siphonophorae), is one of the most recognizable and feared marine organisms in the world, distributed in tropical and subtropical oceanic waters globally and frequently washed ashore on Atlantic and Pacific beaches. Despite superficial resemblance to a jellyfish, it is a colonial siphonophore composed of specialized zooids functioning as a gas-filled pneumatophore float, dactylozooids bearing nematocyst-laden tentacles that can extend up to 50 m, and reproductive gonozooids. Its nematocyst venom causes extreme pain and can be life-threatening to humans. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.