Portuguese Man O' War

The Portuguese war (''Physalia physalis''), also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is the only species in the genus ''Physalia'', which in turn is the only genus in the family Physaliidae. The name ''man o’ war'' comes from the man-of-war, a sailing warship, and the animal's resemblance to the Portuguese version (the caravel) at full sail.

The man o' war are part of the neuston, organisms that live on the surface of the water. A gas-filled bladder provides buoyancy that lets the animal stay afloat on the surface of the water while tentacles which can be up to165 ft (9 to 50 m) long hang below the surface, containing venomous cnidocytes that help capture prey. The cnidocytes can deliver a sting powerful enough to kill fish, and even, in some cases, humans. A sail on the bladder, which may be left or right-handed, propels it about the sea, often in groups. Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore. Like all siphonophores, it is a colonial organism, made up of many smaller units called zooids. Although they are morphologically quite different, all of the zooids in a single specimen are genetically identical. These different types of zooids fulfill specialized functions, such as hunting, digestion and reproduction, and together they allow the colony to operate as a single individual.

Because it frequently washes up on beaches on the coast of the Atlantic, Indian and Pacific Oceans and is seen in the open ocean, the man o' war is the best-known genus of siphonophore, as nearly all siphonophores live in the cold, dark ocean depths where they can only be observed in their natural habitat by a submersible or ROV.

Taxonomy

''Physalia physalis'' is the only species in its genus, ''Physalia'', and family, Physaliidae. The Pacific man o' war, distinguished by a smaller float and a single long fishing tentacle, was originally considered a separate species in the same genus (''P. utriculus''). However, it and other supposed ''Physalia'' species are now considered synonyms of ''P. physalis.''

Description

Like all siphonophores, ''P. physalis'' is a colonial organism: each animal is composed of many smaller units (zooids) that hang in clusters from under a large, gas-filled structure called the pneumatophore. The individual zooids in a colony are evolutionarily derived from either polyps or medusae, i.e. the two basic body plans of cnidarians. Both of these body plans comprise entire individuals in non-colonial cnidarians (for example, a jellyfish is a medusa, while a sea anemone is a polyp). All zooids in a man o' war develop from the same single fertilized egg and are therefore genetically identical. They remain physiologically connected throughout life, and essentially function as organs in a shared body. Hence, a Portuguese man o' war constitutes a single organism from an ecological perspective, but is made up of many individuals from an embryological perspective.

Seven different types of zooids have been described in the man o' war, and these all depend on each other for survival and performing different functions, such as digestion (gastrozooid

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