The incredible life of the immortal jellyfish

Pharaohs built pyramids to immortalise themselves, poets wrote epics, politicians changed the fate of nations, but they all had to die one day. Guess who has cracked the riddle of immortality? There’s only one species that has been called ‘biologically immortal’ by scientists: Jellyfish turritopsis dohrnii. These small, transparent animals drifting about in the ocean can turn back time – they can revert to an earlier stage in their lifecycle – and continue like this forever. That’s why they are called the immortal jellyfish.  

But how does an adult go back to being younger?  

Immortal jellyfish lifecycle  

To understand this amazing phenomenon better, let’s first look at their lifecycle:  

Fertilised egg: an adult jellyfish (called a medusa) lays eggs in the water  

Planula: the fertilised egg grows into a small larva called planula. It’s very small, looks like a worm and can swim  

Polyp: The planula swims down to find a solid surface (such as the seabed, rock or coral), and latches on to it. It starts growing, develops a digestive system and is able to feed itself on fish eggs, worms, and creatures smaller that itself. It starts cloning itself through cell division, and starts its own small colony. 

Ephyra: After forming a new set of muscles and nerves, a section of a polyp (either the original polyp or clone) becomes an ephyra, an organism that can swim independently, grow and feed.

Medusa: The Ephyra grows into an adult jellyfish, called the medusa. 

Cyst: If starved, injured or stuck in waters too cold or hot, an adult turritopsis dohrnii drops to the ocean floor and becomes a tiny blob of tissue (known as a cyst)  

Polyp: The cyst becomes a polyp once again, starting the lifecycle afresh. This is like a butterfly turning back into a caterpillar, or a frog becoming a tadpole again.  

Can the immortal jellyfish be killed?  
Unfortunately, yes. They are consumed by predators or killed accidentally. But scientists have pointed out that there may be some jellyfish who managed to escape danger – which means they have been around since before the dinosaurs – and are truly immortal.