Which animal is often called the Portuguese man o' war but is not a true jellyfish?

Physalia physalis is often called the Portuguese man o' war but is not a true jellyfish.

It is a siphonophore, a colony made of specialized individuals called zooids. These zooids perform different tasks, including floating, feeding, reproduction, and capturing prey. The colony's gas-filled float sits at the sea surface, while long tentacles trail below.

The tentacles contain stinging cells called nematocysts. Contact can cause painful welts, and the tentacles may remain dangerous even after the colony has washed ashore. The animal captures fish and other prey with its tentacles, while specialized zooids digest and distribute nutrients.

A true jellyfish is generally a single medusa organism, although jellyfish can also have complex life cycles. The man o' war's apparent single body hides its colonial organization. Its common name is linked to the shape of its float, which resembles a Portuguese warship's sail.