Jellyfish are very bizarre, they have no eyes, no heart, no brain and are very simple organisms. They are similar to bacteria in that they do not “think” but more react to stimuli in order to escape or feed. In nature, there is one Jellyfish that is weirder than all the rest and that is called Turritopsis Dohrnii or more commonly dubbed “The Immortal Jellyfish”.
Whilst the Jellyfish itself may be quite a simple organism, its life cycle is not. In the development of a full adult jellyfish, the organism goes through several very distinct and different phases in its life. The Jellyfish life starts, as with ours, with a sperm and an egg, once the egg has been fertilized and has developed, the jellyfish hatch as Planula Larva and swim out on their own. These are tiny oval shaped organisms with small hairs called cilia which help propel them through the water. This stage of life is fairly short-lived and after a few days the Planula Larva drops to the bottom of the ocean floor and attaches itself to the rock and transforms
into what is called a Polyp.
In this stage the Polyp is stationary on the sea bed and feeds by drawing passing food into its mouth. Over time the Polyp grows and multiplies, forming into a small colony, it can stay in this form for several years until it is large enough and ready to transform into its final phase. The last stage is called the Medusa, and is the most commonly thought of image when you envision a jellyfish. The medusa jellyfish break away from the Polyp colony and float off into the water.
It is in this stage that jellyfish stay until until they die, however there is one species of jellyfish on the planet that does not do this and is, in fact, a unique specimen among all organisms on Earth; Turritopsis Dohrnii, “The Immortal Jellyfish”. Under times of stress such as food shortage, trauma, illness or old age, this unique jellyfish can once again, drop down to the sea bed, latch onto the rock and revert back into the Polyp stage, from here it can then transform into a colony once more and when the conditions are right can then form back into a full adult jellyfish. These Polyps often produce hundreds of identical clone jellyfish to disperse into the water. When the jellyfish come under stress again, they can repeat the process, reverting back to the Polyp stage and then growing a colony once more, this process makes them potentially immortal and incredibly unique.
However the jellyfish are not completely death-proof, should they be eaten by predators, become removed from the water or overcome with disease they can still die, but theoretically they could live forever.
Further Reading:
what is polyp poo