There may not be an "immortal bird" in the sky, but there are "immortal jellyfish" in the sea.

The Turritopsis dohrnii is tiny, usually about 4-5 mm in diameter, with a bell-shaped body that is transparent or translucent, allowing its internal structure to be clearly seen. The edges of their umbrella-shaped bodies have many slender tentacles, which are not only used to capture and eat plankton, but also to sense changes in the surrounding environment. The tentacles are arranged radially in the lower half of the jellyfish. When they are contracted, the jellyfish appears more compact, and when they are stretched out, the jellyfish appears elegant and graceful.

The body of the Turritopsis dohrnii is mainly composed of two parts: the umbrella and the vertebra. The umbrella is the main part of the jellyfish, which not only protects the internal organs, but also can swim and move by contracting and expanding. The vertebra is located below the umbrella, connecting the stomach cavity and the oral arms, and is the location of the digestive system and reproductive system. The Turritopsis dohrnii got its name because its reddish, lighthouse-shaped gonad is very eye-catching. When the gonad matures, it will emit a red light, shaped like a lighthouse, hence the name Turritopsis dohrnii.

This tiny creature, first discovered in the Caribbean Sea, has the magical ability to "rejuvenate". Normally, jellyfish die after reproducing the next generation, but after reaching sexual maturity, the "Turritopsis dohrnii" will return to its youthful stage and begin another life cycle. In theory, this process is cyclical and can continue forever, that is, as long as the Turritopsis dohrnii is not attacked by natural enemies or infected with diseases, it will live forever.

Jellyfish are usually fertilized externally. The fertilized eggs will slowly develop into planktonic larvae in the incubation of seawater. After a period of planktonic life, the larvae will become very small trumpet-shaped polyps. After a period of development, they will split into two halves, and each part will develop into a transverse body. When the transverse body grows up, it will separate from the mother polyp, turn upside down in the sea to become an independent disc-shaped body, and begin its free planktonic life, and slowly grow into a jellyfish body. After the sexually mature jellyfish completes the mission of passing on offspring, it will gradually lose its vitality and melt into the sea.

But even an adult Turritopsis dohrnii can reverse into an immature larva. This is also the most amazing feature of the Turritopsis dohrnii - "immortality", that is, it can turn back into a polyp within three days when faced with threats such as hunger, injury, and environmental changes. Through the cell transdifferentiation mechanism, it reshapes itself into a young larvae, thus achieving "rejuvenation". When everything is calm, the polyp will grow into a jellyfish again. It's like a butterfly suddenly gets tired of flying and goes back into the pupa.

Under laboratory conditions, scientists have observed that the Turritopsis dohrnii can repeat this process more than ten times, or even more. Each time it reverses, its cells return to their initial state, as if pressing the "reset button" of life. This phenomenon is extremely rare in other organisms, and even a similar mechanism has not been found in humans. Therefore, the Turritopsis dohrnii's reverse growth process provides scientists with a unique window to explore the essence of life and the mechanism of aging.

Through the process of rebirth, one jellyfish becomes hundreds of identical jellyfish. This also explains why the world's five oceans are full of dohrnii jellyfish with almost identical genetic arrangements. Scientists believe that the possibility of humans replicating the rejuvenation process of the dohrnii jellyfish is extremely slim. "It is too early to conclude that the dohrnii jellyfish can help humans regain youth and immortality. No one is studying this yet," said Miletta, "and I don't think you can find any secrets from it." However, by studying how the cells of the dohrnii jellyfish complete the above process, it can effectively help scientists find clues to deal with those stubborn and fast-spreading invading viruses. If this ability can be applied to human medicine, it will be possible to provide new methods for treating various tissue injuries and diseases.

References:

[1] Xu Jianpeng. The “rejuvenating” Turritopsis jellyfish[J]. Discovery Channel.

[2] Can it really make people immortal? [J]. Jingjing Campus.

[3] Han Xuyang. The secret of the immortal jellyfish's "reverse growth"[J]. Science and Technology.

[4] Chen Chunquan. Phoenix Nirvana: “Immortal” Jellyfish[J]. Interesting Nature.