The Portuguese man o' war, also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or bluebottle, which is found mainly in the Pacific Ocean. The Portuguese man o' war is the only species in the genus Physalia, which in turn is the only genus in the family Physaliidae.
Portuguese man o' war
The name comes from the animal’s resemblance to a sailing warship, the Portuguese man-of-war (the caravel)
Blue dragon
Violet snail
Hydrozoa is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater habitats. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
Hydrozoa
The hydroid Tubularia indivisa, fertile, Gulen Dive resort, Norway
The highly apomorphic Siphonophorae—like this Portuguese man o' war (Physalia physalis)—have long misled hydrozoan researchers.
Limnomedusae like the flower hat jelly (Olindias formosa) were long allied with Anthomedusae and Leptomedusae in the "Hydroida".