1. Turritopsis dohrnii

Nicknamed the “immortal jellyfish,” this tiny marine creature has an almost sci-fi ability. When stressed or injured, it can revert from its adult medusa stage to its juvenile polyp form through a process called transdifferentiation, in which its cells transform into different types. In theory, this reset button could be pressed repeatedly. In reality, most don’t live forever due to predators or disease — but the biological trick is remarkable.

Through a rare process called transdifferentiation, the adult cells are reprogrammed to become young polyp cells (Image: Gemini Generated)

2. Hydra

Hydra are small freshwater relatives of jellyfish that seem to age so little. Scientists describe them as showing “negligible senescence,” meaning they don’t exhibit the usual signs of physical decline over time. Their secret lies in constantly active stem cells that keep renewing their tissues. In laboratory conditions, they can maintain this regenerative ability indefinitely.

3. Axolotl

The axolotl, a Mexican salamander, is famous for its almost magical healing powers. It can regrow limbs, parts of its spinal cord, sections of the heart, and even brain tissue — all without scarring. While it doesn’t literally reverse ageing, its ability to form a regeneration structure called a blastema allows it to repair damage in ways most vertebrates cannot.

Despite maintaining a juvenile appearance, axolotl can live for 10 to 20+ years. (Image: Pexels)

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4. Lobster

Lobsters are often labelled “biologically immortal” because they continue producing telomerase, an enzyme that repairs DNA, throughout their lives. This allows them to keep growing and moulting even at large sizes, and they can remain fertile for decades. Some have been known to live beyond 50 years. However, they don’t age backwards. As they grow bigger, moulting becomes more dangerous and energy-intensive, and many eventually die from size-related complications like moulting failure rather than traditional ageing.

5. Planarian

Planarians are characterised by a three-branched intestine (Image: Wikimedia Commons)

Planarians (triclads) are free-living flatworms that include hundreds of species, found in freshwater, marine, and terrestrial habitats. These simple flatworms have astonishing regenerative powers. Thanks to special stem cells called neoblasts, they can regrow an entire body from just a fragment. This whole-body renewal means they show negligible senescence and, under ideal conditions, may live indefinitely.