The pneumatophore functions as both a flotation device and a sail for the colony, allowing the colony to move with the prevailing wind. It is translucent and tinged blue, purple, pink, or mauve, and may be 9 to 30 centimetres ( 3 + 1⁄ 2 to 12 inches) long and rise as high as 15 cm (6 in) above the water. The pneumatophore, or bladder, is the most conspicuous part of the man o' war. However, naming and categorization of zooids varies between authors, and much of the embryonic and evolutionary relationships of zooids remains unclear. As many as seven different kinds of zooids have been described in the man o' war: three of the medusoid type (gonophores, nectophores, and vestigial nectophores) and four of the polypoid type (free gastrozooids, tentacle-bearing zooids, gonozooids and gonopalpons). New zooids are added by budding as the colony grows.
Just like all siphonophores, the Portuguese man o' war is colonial: each man o' war is composed of many smaller units (zooids) that hang in clusters from under a large, gas-filled structure called the pneumatophore. All zooids in a colony are genetically identical, but fulfill specialized functions such as feeding and reproduction, and together allow the colony to operate as a single individual. Like all siphonophores, it is a colonial organism, made up of many smaller units called zooids. Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore. It has numerous venomous microscopic nematocysts which deliver a painful sting powerful enough to kill fish, and has been known to occasionally kill humans. The Portuguese man o' war is the only species in the genus Physalia, which in turn is the only genus in the family Physaliidae. It is considered to be the same species as the Pacific man o' war, which is found mainly in the Pacific Ocean. The Portuguese man o' war ( Physalia physalis), also known as the man-of-war, bluebottle, or blue bottle jellyfish, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean.