Jan 26
Portuguese man o' war photo

The float of a Portuguese man o' war.

It’s Australia Day today, giving us the perfect excuse to explore one of Australia’s most unique and interesting species – the Portuguese man o’ war

While not an exclusive Aussie resident, anybody who has taken a dip in Australian waters will surely have heard of this intriguing species. 

Famed for its potent sting, the Portuguese man o’ war is often mistaken for a jellyfish. However, if you take a closer look at the biology of these animals, you’ll quickly see that they are very different. 

Portuguese man o’ wars, known in Australia as bluebottles, are colonial organisms which belong to the order Siphonophora. While true jellyfish each constitute an individual animal, bluebottles are the product of many individuals of the same species working together in close association. 

Called polyps, these individuals are highly specialised and would be unable to survive without one another. 

Probably the most familiar member of this colony is the float, a single oversized polyp filled with gas. Known as a pneumatophore, it is able to regulate the amount of gas within itself to control the depth of the whole colony. Its also the polyp responsible for the man o’ war’s unusual name, resembling the sails of man-of-war battleships in both appearance and function. 

A fearsome reputation 

While the pneumatophore accounts for the species’ namesake, the tentacles are what give the species its fearsome reputation. Packed with venomous stinging cells called nematocysts, the tentacles are large dactyzooid polyps. Primarily serving to entrap prey items such as fish, dactyzooids also function as an effective form of defence and may reach lengths of more than 20 meters. 

Portuguese man o' war photo

Fish prey caught among the animal's dactyzooid tentacles.

Digestion is taken care of by a large number of small gastrozooids, while reproductive polyps are called gonozooids. Within each colony, gonozooids may be either male or female, releasing sperm or eggs into the water during the breeding season to join with those of another colony. As larvae grow, they divide asexually into the four polyp types (zooids) to form an adult colony.

Portuguese man o' war photo

A close-up of the bluebottle's reproductive gonozooids.

So there you have it, a quick look at the incredible biology of the Portuguese man o’ war. If anybody tries to claim they are a jellyfish again, you’ll know exactly what to say! 

And by the way, if you are ever in an area where the Portuguese man o’ war is likely to be around, make sure you know the appropriate first aid techniques in case of a sting. 

Take a look at the ARKive profile to see more incredible images of the Portuguese man o’ war. 

Rob Morgan, ARKive Media Reseacher