DiscoverScroll article

The Portuguese man o' war (Physalia physalis), also known as the man-of-war, bluebottle, or sometimes called Caravela Portuguesa (a name of Portuguese origin), is a marine hydrozoan found in the Atlantic, Indian, and Pacific oceans.

Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore. The man o' war is part of the neuston, organisms that live on the surface of the water. A gas-filled bladder called the pneumatophore provides buoyancy that lets the animal stay afloat on the surface of the water while its tentacles, which can be up to 30 m (100 ft) long, hang below the surface, containing venomous cnidocytes that help capture prey. A sail on the pneumatophore propels it about the sea, sometimes in groups as large as 1,000 individuals.

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 Portuguese man o' war was first described by Carl Linnaeus in the 10th edition of his Systema Naturae under the name Holothuria physalis.

Like all siphonophores, the man o' war 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. All zooids in a man o' war develop from the same single fertilized egg and are therefore genetically identical. 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 (gastrozooids), reproduction (gonozooids) and hunting (dactylozooids). The pneumatophore or bladder is the most conspicuous part of the man o' war. Large groups of Portuguese man o' war, sometimes over 1,000 individuals, may reduce fishery populations.

The Portuguese man o' war is well known to beachgoers for the painful stings delivered by its tentacles.

The Portuguese man o' war is a carnivore. The organism has few predators; one example is the loggerhead sea turtle, which feeds on the Portuguese man o' war as a common part of its diet. The blue sea slug (aka blue dragon) also specializes in feeding on the Portuguese man o' war, as does the violet sea snail. The ocean sunfish's diet, once thought to consist mainly of jellyfish, has been found to include many species, including the Portuguese man o' war.

The Portuguese man o' war is often found with a variety of other marine fish, including yellow jack. These fish benefit from the shelter from predators provided by the stinging tentacles, and for the Portuguese man o' war, the presence of these species may attract other fish to eat. The blanket octopus is immune to the venom of the Portuguese man o' war. The man-of-war fish is known to be able to live surrounded by the tentacles of the Portuguese man o' war, having at least one antigen to the man o' war's toxin, although still avoids being stung by swimming around them.

The stinging, venom-filled nematocysts in the tentacles of the Portuguese man o' war can paralyze small fish and other prey.

Stings from a Portuguese man o' war can result in severe dermatitis characterized by long, thin, open wounds that resemble those caused by a whip.

The Portuguese man o' war is asymmetrically shaped: the zooids hang down from either the right or left side of the midline of the pneumatophore or bladder.

This model assumed the man o' war was advected by the surface currents, with the effect of the wind being added with a much higher wind drag coefficient of 10%.

Quick Facts

• Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore.
• The man o' war is part of the neuston, organisms that live on the surface of the water.
• The Portuguese man o' war is a carnivore.
• The man-of-war fish is known to be able to live surrounded by the tentacles of the Portuguese man o' war, having at least one antigen to the man o' war's toxin, although still avoids being stung by swimming around them.
• Large groups of Portuguese man o' war, sometimes over 1,000 individuals, may reduce fishery populations.

Source material: Wikipedia - "Portuguese man o' war". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.