Physalia Utriculus

The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, 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 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, the community of organisms that live at the ocean surface. It has numerous venomous microscopic nematocysts which deliver a painful sting powerful enough to kill fish, and has been known to occasionally kill humans. 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. 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, a sailing warship, and the animal's resemblance to the Portuguese version (the caravel) at full sail.

Overview

The siphonophore ''Physalia physalis'', commonly known as the Portuguese man o' war, is one of the most conspicuous, but poorly understood, members of the neuston. The neuston 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 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. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License

The development, morphology, and colony organization of ''P. physalis'' is very different from all other siphonophores. Siphonophores are a relatively understudied group of colonial hydrozoans. Colonies are composed of functionally specialized bodies (termed zooids) that are homologous to free living individuals. Most species are planktonic 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, by hand while blue-water diving, or in regions with localized upwellings. 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 colonial organism composed of small individual animals called zooids. 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 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. New zooids are added by budding 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 gastrozooids, tentacle-bearing zooids, gonozooids and gonopalpons). However, naming and categorization of zooids varies between authors, and much of the embryonic and evolutionary relationships of zooids remains unclear.

The pneumatophore, or bladder, is the most conspicuous part of the man o' war. It is translucent and tinged blue, purple, pink, or mauve, and may be long and rise as high as above the water. The pneumatophore functions as both a flotation device and a sail for the colony, allowing the colony to move with the prevailing wind. The gas in the pneumatophore is part carbon monoxide (0.5–13%), which is actively produced by the animal, and part atmospheric gases (nitrogen, oxygen and noble gases) that diffuse in from the surrounding air. In the event of a surface attack, the pneumatophore can be deflated, allowing the colony to temporarily submerge.

The colony hunts and feeds through the cooperation of two types of zooid: gastrozooids and tentacle-bearing zooids known as dactylozooids or tentacular palpons. The dactylozooids are equipped with tentacles, which are typically about in length but can reach over . Each tentacle bears tiny, coiled, thread-like structures called nematocysts. Nematocysts trigger and inject venom on contact, stinging, paralyzing, and killing adult or larval squids and fishes. Large groups of Portuguese man o' war, sometimes over 1,000 individuals, may deplete fisheries. Contraction of tentacles drags the prey upward, into range of the gastrozooids, the digestive zooids. The gastrozooids surround and digest the food by secreting enzymes. ''P. physalis'' typically has multiple stinging tentacles, but a regional form (previously known as a separate species, ''P. utriculus'') has only a single stinging tentacle.

The main reproductive zooids, the gonophores, are situated on branching structures called gonodendra. Gonophores produce sperm or eggs (see life cycle). Besides gonophores, each gonodendron also contains several other types of specialized zooids: gonozooids (which are accessory gastrozooids), nectophores (which have been speculated to allow detached gonodendra to swim), and vestigial nectophore

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