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. While it is typically considered the only species in its genus, Physalia, and family, Physaliidae, genetic evidence suggests there may be more. 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. 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. The cnidocytes can deliver a sting powerful enough to kill fish, crustaceans, and in some cases, humans. A sail on the pneumatophore propels it about the sea, sometimes in groups as large as 1,000 individuals. The sail may be left or right-handed, being so assigned on the basis of the direction in which the wind catches it.
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. The genus name Physalia and species name physalis are both derived from the Greek word physalis, meaning "bubble" or "bladder".
Taxonomy The Portuguese man o' war was first described by Carl Linnaeus in the 10th edition of his Systema Naturae under the name Holothuria physalis. The species was moved to the genus Physalia by Jean-Baptiste Lamarck in 1801 and family Physaliidae by Brandt in 1835. Although siphonophore systematists have often treated Physalia as monotypic (with Physalia physalis as the only species), both morphological and genetic studies have suggested that Physalia includes multiple distinct lineages and may comprise more than one species. Historically, proposed splits within Physalia were often based on morphology; for example, P. utriculus, identified by a smaller float and a single long fishing tentacle, is often considered a separate species. These characteristics however are also present in juvenile specimens of P. physalis. Other morphological evidence has proved inconclusive as well; while variation does exist, it has been difficult to determine whether it represents separate species or variation within a single species. Genetic evidence suggests that different species do indeed exist. A 2012 study using specimens from New Zealand identified three distinct lineages and the existence of up to ten species or possibly a species complex. A 2025 study using specimens from around the world identified five clear lineages representing at least four distinct species: P. minuta which has a small green-tinted pneumatophore with a short sail and short tentacles from the Southwest Pacific; P. megalista which has a long and slender pneumatophore from the South Pacific, South Atlantic and South Indian; P. utriculus which has a short sail and single tentacle found worldwide; as well as the original P. physalis from the Atlantic. In 2025, Physalia mikazuki was described as a new species from Sendai Bay (Tohoku, Japan), supported by diagnostic morphology and mitochondrial phylogenies (16S rRNA and COI).
Phylogeny Physaliidae is one of two families, the other being Rhizophysidae, in the siphonophore suborder Cystonectae. Cystonectae was the earliest group of siphonophores to diverge, and as such maintain many ancestral characteristics, such as dioecy and the presence of palpons. The below cladogram is based on Munro and colleagues (2018).
Description
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