Does the Immortal Jellyfish Actually Live Forever?

The immortal jellyfish is a translucent creature measuring about 3 to 4.5 millimeters (about 0.1 inches) in diameter when fully grown. That's about the size of a small stud earring.

It is bell-shaped, with a smooth, dome-like body, and it has up to 90 delicate tentacles extending from its edges (though as juveniles, these jellies have only eight tentacles). Through the transparent body, you can see the immortal jellyfish's bright red stomach.

Immortal jellyfish are part of the Cnidaria group, which is also where corals and sea anemones are classified in animal taxonomy.

The life cycle of the immortal jellyfish is what makes it extraordinary. Like most jellyfish species, it begins life as a larva, which settles on a surface and grows into a polyp, which is a blob-like cyst. This is the stage where the jellyfish is still attached to the sea floor.

This polyp then transforms into a medusa, which is the free-swimming stage of an adult jellyfish. And the medusa is generally the final stage of a typical jellyfish's life before it dies.

But immortal jellyfish — when faced with stress, injury or starvation — have the ability to revert back into a polyp. Through a process known as transdifferentiation, they are essentially resetting their biological clocks to cheat death.

The reincarnated polyp eventually produces new medusae that are genetically identical to the previous version of the immortal jellyfish. This process is called transdifferentiation, where mature cells transform back into stem-like cells or polyp cells, allowing for regeneration of a whole new body.

The immortal jellyfish can repeat this life cycle reversal indefinitely, which helps it survive in changing environments and unfavorable conditions.

In reality, because the immortal jellyfish is tiny and easily preyed upon, the immortal jellyfish is frequently eaten by fish, sea turtles, slugs and other sea creatures — so they are perfectly capable of dying.

But even if they do regenerate forever, this begs a question of science fiction and philosophy: If all of an immortal jellyfish's cells are replaced but perfectly duplicated, is it technically the same jellyfish?

Scientists have been studying the immortal jellyfish to see if they can learn anything about extending the lives of people.

Though human beings may not be able to magically revert to a youthful state in the same way, the research may give new insights into stem cell research, as scientists discover new ways to replace cells that have been damaged by disease.

The adult immortal jellyfish is a solitary creature, spending most of its life drifting through the ocean. But during the polyp stage of its life cycle, polyp colonies may form on surfaces such as rocks or seaweed.

The immortal jellyfish is a carnivore, feeding on tiny plankton, fish eggs and other microscopic organisms floating in the water.

It uses its tentacles, which are lined with stinging cells called nematocysts, to capture and immobilize its prey. This efficient feeding method allows the jellyfish to thrive in various ocean environments.

We created this article in conjunction with AI technology, then make sure it was fact-checked and edited by a HowStuffWorks editor.