The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine

hydrozoa Hydrozoa (hydrozoans; ) are 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 specializ ...

n found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, 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. The Portuguese man o' war is a conspicuous member of the

neuston Neuston, also known as pleuston, are organisms that live at the surface of the ocean or an estuary, or at the surface of a lake, river or pond. Neuston can live on top of the water surface or may be attached to the underside of the water surface. ...

, the community of organisms that live at the ocean surface. It has numerous venomous microscopic

nematocysts A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this c ...

which deliver a painful

sting Sting may refer to: * Stinger or sting, a structure of an animal to inject venom, or the injury produced by a stinger * Irritating hairs or prickles of a stinging plant, or the plant itself Fictional characters and entities * Sting (Middle-eart ...

powerful enough to kill fish, and has been known to occasionally kill humans. Although it superficially resembles a

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

, the Portuguese man o' war is in fact a

siphonophore Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...

. Like all siphonophores, it is a

colonial organism In biology, a colony is composed of two or more conspecific individuals living in close association with, or connected to, one another. This association is usually for mutual benefit such as stronger defense or the ability to attack bigger prey. ...

, made up of many smaller units called

zooid A zooid or zoöid is a single animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooi ...

s. 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.

Taxonomy

The blue bottle, Pacific man o' war or Indo-Pacific Portuguese 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''). The name was synonymized with ''P. physalis'' in 2007, and it is now considered a regional form of the same species.

Etymology

The name ''man o' war'' comes from the

man-of-war The man-of-war (also man-o'-war, or simply man) was a Royal Navy expression for a powerful warship or frigate from the 16th to the 19th century. Although the term never acquired a specific meaning, it was usually reserved for a ship armed wi ...

, a sailing warship, and the animal's resemblance to the Portuguese version (the

caravel The caravel (Portuguese: , ) is a small maneuverable sailing ship used in the 15th century by the Portuguese to explore along the West African coast and into the Atlantic Ocean. The lateen sails gave it speed and the capacity for sailing win ...

) at full sail.

Overview

The

''Physalia physalis'', commonly known as the Portuguese man o' war, is one of the most conspicuous, but poorly understood, members of the neuston. The

is the floating community of ocean organisms that live at the interface between water and air. This community is exposed to a unique set of environmental conditions including prolonged exposure to intense ultraviolet light, desiccation risk, and rough sea and wave conditions. Despite their tolerance for extreme environmental conditions and the very large size of this habitat, which makes up 71% of the Earth’s surface and is nearly three times the area of all terrestrial habitats, very little is known about the organisms that make up this highly specialized polyphyletic community. The Portuguese man o' war is aptly named after a warship: it uses part of an enlarged float filled with

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

and air as a sail to travel by wind for thousands of miles, dragging behind long tentacles that deliver a deadly venomous sting to fish. This sailing ability, combined with a painful sting and a life cycle with seasonal blooms, results in periodic mass beach strandings and occasional human envenomations, making ''P. physalis'' the most infamous siphonophore. CC-BY icon

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The development, morphology, and colony organization of ''P. physalis'' is very different from all other siphonophores. Siphonophores are a relatively understudied group of

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

hydrozoan Hydrozoa (hydrozoans; ) are 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 ...

s. Colonies are composed of functionally specialized bodies (termed

s) that are homologous to free living individuals. Most species are

planktonic Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

and are found at most depths from the deep sea to the surface of the ocean. They are fragile and difficult to collect intact, and must be collected by submersible,

remotely operated vehicle A remotely operated underwater vehicle (technically ROUV or just ROV) is a tethered underwater mobile device, commonly called ''underwater robot''. Definition This meaning is different from remote control vehicles operating on land or in the ai ...

, by hand while blue-water diving, or in regions with localized

upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...

s. However, ''Physalia physalis'' is the most accessible, conspicuous, and robust siphonophore, and as such, much has been written about this species, including the chemical composition of its float, venom (especially envenomations), occurrence, and distribution. Fewer studies, however, have taken a detailed look at P. physalis structure, including development, histology of major zooids, and broader descriptions of colony arrangement. These studies provide an important foundation for understanding the morphology, cellular anatomy, and development of this neustonis species. It can be difficult to understand the morphology, growth, and development of ''P. physalis'' within the context of siphonophore diversity, as the colony consists of highly 3-dimensional branching structures and develops very different from all other siphonophores. The bluebottle resembles a jellyfish but is actually a siphonophore, a

composed of small individual animals called

s. There are four zooids depending on each other for survival and performing different functions, such as digestion (gastrozooids), reproduction (gonozooids) and hunting (dactylozooids). The last zooid, the pneumatophore, is a gas-filled float or sac that supports the other zooids and acts like a sail so the bluebottle is constrained to the ocean surface, moving at the mercy of the wind, waves and marine currents. The bluebottle's long tentacles hang below the float as they drift, fishing for prey to sting and drag up to their digestive zooids.Totton, A. and Mackie, G. (1960) "Studies on Physalia physalis", ''Discovery Reports'', 30: 301–407. The species is found throughout the world's oceans, in tropical, subtropical and (occasionally) temperate regions.

Anatomy and physiology

File:Anatomy of a Physalia physalis colony.png, Anatomy of a Physalia physalis colony
with descriptions of the function of each zooid Like all siphonophores, the Portuguese man o' war is

: each man o' war is composed of many smaller units (

s) that hang in clusters from under a large, gas-filled structure called the pneumatophore. New zooids are added by

budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is know ...

as the colony grows. 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

gastrozooid {{Short pages monitor