Are some jellyfish really immortal? 

As we all know, nature is full of amazing varieties of flora and fauna. They’re blessed with unique characteristics that charm and surprise us. One of their most important characteristics is life span. Some creatures, such domesticated dogs, sadly lead relatively short lives. But there are other creatures that live for so long that they’re mistaken as immortal. An example of this is the bowhead whale, which enjoys a life span of 200 years. Does this number surprise you? Well, that’s nothing compared to the life spans of the Greenland Shark and the Atlantic Sponge; both these creatures live for thousands of years. But perhaps only one creature is actually thought to live forever—the Turritopis dohrnii jellyfish.  

Let’s try to crack the mystery of the never-ending life span of the Turritopis dohrnii jellyfish.  

Turritopsis dohrnii: The only known immortal creature
Nope, this isn’t a joke. While Antarctic Sponges still die at some point, the Turritopis dohrnii jellyfish is believed to never die. That’s why it has fondly been nicknamed the immortal jellyfish. So, what’s the secret behind this jellyfish’s immortality? In a nutshell, it reverts to its juvenile polyp stage after maturity and this process keeps repeating in a loop.  

Before delving further into the immortal jellyfish, let’s first understand how a normal jellyfish matures. 

Jellyfish biology 
The life cycle of normal or ‘mortal’ jellyfish unfolds in five stages. It all begins when the jellyfish is a fertilized egg; this egg then grows into a larva called planula, which resembles a freely moving microscopic worm. Subsequently, the planula enters the polyp stage, wherein it swims downwards and develops digestive and reproductive systems, the former of which enables it to feed itself. As a result, the planula transforms into a polyp. Following this, the polyp develops muscles and nerves and changes into an ephyra. At this stage, the jellyfish is ready to grow on its own and move about freely. After a given period of time, the ephyra turns into a fully-grown adult jellyfish or medusa. Fast forward a few years, it dies due to its natural life cycle. 

Now let’s circle back to the immortal jellyfish. This jellyfish also goes through the exact same process as normal jellyfish. However, unlike normal jellyfish, it doesn’t grow old and die. Rather, when faced with old age or threats, such as injury and starvation, it simply retracts its tentacles, shrinks its body and sinks to the ocean floor. Thereafter, it transforms into a tiny jelly blob, called a cyst, and reverts to its polyp stage. In fact, it can go back and forth between the medusa and polyp stages unlimited times. You’re probably wondering how it’s able to do this, aren’t you? That’s because it possesses a special ability to go through a process called cellular transdifferentiation.  

To understand what this process is all about, let’s hear directly from the head of The Real Immortal Jellyfish research project, Maria Pia Miglietta. According to her, “This is basically when a fully formed specialized adult cell can become another type of specialized adult cell. It’s how a cell can adapt.” So, simply put, something cellular happens in its cyst stage that helps the medusa change into a polyp. While the exact reason for this is still unknown, it’s presumed to be related to DNA. Here’s another fun and interesting fact—the immortal jellyfish also lacks the two most important organs, the heart and the brain. Whether this also has something to do with its eternal life remains a mystery.  

In this way, an immortal jellyfish’s life span follows an endless cycle, young to old and back to young again. And one thing’s for sure, it’s almost as if their bodies refuse to die of natural causes. So, if one day you ever hear that a Turritopis dohrnii jellyfish has died, know that it’s probably an accident or the result of a predator or disease.   

Interestingly, this process of immortality still hasn’t been observed under natural surroundings, but only in laboratories.