Portuguese Man-of-War, a floating, compound marine animal found in warm regions of all oceans. It is made up of a colony of four kinds of polyps (individual, tubular water animals). One kind of polyp forms the gas-filled float, 8 to 10 inches (20 to 25 cm) long, which is usually iridescent blue with a pink crest. Below the float hang the food-catching, feeding, and reproductive polyps. The food-catching polyps form tentacles that may be more than 40 feet (12 m) long, with stinging parts that paralyze or kill most fish and other prey on contact. (For a notable exception, The feeding then polyps close around the prey and digest it. The sting is painful to humans and can cause nausea and convulsions.

The Portuguese man-of-war is a cnidarian belonging to the genus Physalia of the order Siphonophora.