The Portuguese Man-Of War is another one of the stinging jellyfish, it is more common and widespread than either the box jellyfish or sea wasp. It is however not as deadly as the sea wasp. The Portuguese man-o-war (Physalia physalis), is more commonly referred to as the blue bottle in Australia. It is found throughout the world, in warmer seas and its habitat generally encircles Australia and extends to Tasmania, as well. The Portuguese man-o-war is most common in the summer months in shallow, coastal waters. Bluebottles usually frequent exposed ocean beaches after strong onshore winds, they are rarely found in sheltered waters. The Portuguese man-o-war is commonly observed in the open ocean and coastal seas, and is often mistaken for a true jellyfish.

The Portuguese man-o-war is not a single marine animal, but it is a colonial hydroid, consisting of a large colony of smaller marine organisms, each of them is responsible for specific biological functions. The blue-bottle gets its name from the body, which really is a large, gas- filled, bladder-like blue float, that can be up to 30 centimeters in length and rise above the water as much as 15 centimeters. The float has a crest, that is used much as a sail to propel the colony across the water when the wind blows. Clusters of colonial polyps are attached to the underside of the blue bladder, for digestion and reproduction. Bluebottles are hermaphrodites, the fertilized egg develops into a planktonic larval form that produces the large Physalia colony by asexual budding. Lastly it has very long tentacles (sometimes up to 10 meters in length) extend from each of the polyps. Each of the tentacles has stinging cells (called nematocysts) that are capable of killing fish up to 10 centimeters long. Its favourite food consists of surface plankton. The poison secreted from the nematocysts of the Portuguese man-o-war causes respiratory problems and muscle weakness, and it is through these actions that the Portugese man-o-war captures and kills its prey.