Siphonophores are marine invertebrates that look like a single organism but actually consist of a colony of many individual animals.

Portuguese Man of War   ©  Magnus Lundgren

Some siphonophora superficially resemble jellyfish, like the best known species of this kind:
The dangerous Portuguese Man o’ War.
Others form one of the longest animals in the world, reaching up to 50 metres in length.

In this unique collaboration of a life form underwater, each individual animal fulfils an important role in the existence of the super-organism that it is part of. One animal is dedicated to catching and digesting prey, another nearby attached individual solely exists to secure reproduction.

Most of these colonies are long and thin with a transparent bell shaped body floating near the surface in the open ocean.

The most commonly known species would be the jellyfish resembling Portuguese Man o’War (Physalia physalis). It is also known as Man-Of-War, or Bluebottle while most people recognise this dangerous animal for its lethal stinging cells.

The man-of-war comprises four separate polyps. The uppermost is formed by a blue gas-filled bladder, so called pneumatophore, which floats above the water.
The tentacles are the man-of-war’s second organism. These long, thin tendrils can extend 50 meters (165 feet) in length below the surface, although 10 meters (30 feet) is the average. They are covered in venom-filled stinging cells which are used to paralyse and kill fish or any other bite-sized creature that crosses their path.
Muscles in the tentacles draw prey up to a polyp containing the gastrozooids or digestive organisms. A fourth polyp contains the reproductive organisms.

For humans, a man-of-war sting is excruciatingly painful, but rarely deadly.
Man-of-wars are found, sometimes in groups of 1,000 or more, floating in warm waters throughout the world’s oceans. They have no independent means of propulsion and either drift on the currents or catch the wind with their pneumatophores. To avoid threats on the surface, they can deflate their air bags and briefly submerge.

With a body length of 40–50 m, another species of siphonophore, Praya dubia, builds one of the longest animals in the world. This organism is sometimes referred to as Swimming Bell and lives 700 to 1000 metres below the surface in the South Atlantic deep sea.
This giant of the deep has a long string of small circle-like bells, the stinging organisms, which make up most of the body.
One end of the animal forms a dome like bell which houses the animals nectosome (swimming bells). Much like their Man o’War relatives, these animals hunt actively and use a blue bioluminescent light to attract prey into its net of paralysing stingers.

Praya dubia has been known to science since the nineteenth century, but its length was only discovered 1987 when technological advances finally enabled researchers to observe this animal in its natural habitat.

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