The Portuguese man o' war isn't a jellyfish. It's a colony that sails.
It looks like a single jellyfish with a gas-filled float, but a Portuguese man o' war is a colony of specialised units called zooids, all cloned from one egg and working as a single body. It has no way to swim. Instead it sails the ocean surface on its float, left- or right-handed.
The man o' war is a siphonophore, a relative of jellyfish named for its resemblance to a Portuguese warship under sail. Each colony grows from one fertilised egg, which buds off new zooids. Seven types have been described, each with a job: some catch prey, some digest it, some reproduce. They derive from the two basic body plans of the group, the polyp and the medusa, which in other species are separate animals. Here they stay connected and function like organs. Ecologically it is one organism; embryologically it is many.
The most visible part is the pneumatophore, a gas-filled float up to about 30 centimetres long. The gas is mostly air, but can contain up to 13 per cent carbon monoxide made by the animal itself. If attacked at the surface, the colony can deflate the float and briefly sink. Beneath it hang tentacles, typically around 10 metres long and sometimes more than 30, armed with stinging cells that paralyse fish and other prey, which are then drawn up to the digestive zooids.
Unable to swim, the colony goes where the wind takes it, sailing at roughly 45 degrees to the wind thanks to its sail and the drag of its tentacles. Colonies come in mirror-image left- and right-handed forms that veer in opposite directions, which may stop a single wind from driving a whole population ashore. When they do strand, sometimes in huge numbers, detached tentacles and dead animals can still sting for hours or even days. In Australia, where it is called the bluebottle, it causes up to 10,000 stings each summer.
A few animals exploit it. Loggerhead turtles eat it, protected by thick skin, and the blue sea slug specialises in it. Blanket octopuses carry broken man o' war tentacles as weapons, and the man-of-war fish lives among the tentacles, nibbling them while perhaps luring other fish in. Long treated as a single species, the man o' war now looks, on genetic evidence, like several, with new species described as recently as 2025.
Source: Wikipedia — Portuguese man o' war · Text summarised from Wikipedia (CC BY-SA 4.0)
