Popular books and movies depicting immortal beings – vampires, werewolves, and other fantastical creatures – have superb entertainment value. They make us wonder what it would be like to live forever, and they give us a renewed understanding of just how precious life is; after all, it is fleeting, and it’s up to each of us to make the most of every day we’re given. What does all this have to do with marine life? The answer lies in the vibrant red, pulsating center of a lovely little jellyfish discovered in Italy in 1988. The Immortal Jellyfish has the ability to grow to maturity, then transform itself back into a polyp, after which it begins life anew.
The Immortal Jellyfish
Biological immortality does not prevent Immortal Jellyfish from being preyed upon by other animals, and it does not prevent it from succumbing to disease. What it does do, is allow the animal to reverse its life cycle and bypass natural death.
Most jellyfish have a fixed life span that ranges from several hours to several months. The Immortal Jellyfish, or Turritopsis Nutricala, is the only jellyfish known to have the capacity to return to its polyp state via a specific transformation process called transdifferentiation. During this process, the animal’s bell and tentacles deteriorate. Next, new tissues grow, and finally, new feeding polyps develop. The polyps multiply and form colonial hydroids that bud new jellyfish, which measure a tiny 1mm across when released. They feed on plankton as they grow, and become sexually mature after 18 to 30 days, depending on water temperature. These jellyfish are able to spawn, with egg masses developing into new polyp colonies that start the life cycle all over again.
The Immortal Jellyfish is tiny, even as an adult specimen. Its maximum diameter is about 4.5mm, and it is usually about the same length. Thin, clear jelly forms its body, which has a bright red, cross-shaped mark on the stomach. Young specimens have just eight tentacles, while adults can have as many as eighty to ninety tentacles.
These jellyfish are thought to have originated in the Caribbean; however, they have spread all over the world, now being found throughout temperate to tropical regions in all oceans. The widespread colonization of Immortal Jellyfish is thought to be the result of ships taking in and discharging water used for ballast.
Science has yet to unlock the secret of the Immortal Jellyfish’s reverse aging process. Partly, this is due to the fact that the animals are difficult to cultivate in captivity, and partly that only a few hydroid experts seem interested in working with them. One such expert is Shin Kubota, a Japanese biologist from Wakayama Prefecture. He keeps about 100 Immortal Jellyfish specimens in petri dishes in his laboratory, carefully feeding them minced brine shrimp every eight hours or so. He carries his jellies with him in a cooler when he travels, and he firmly believes that jellyfish form the roots of the fabled Tree of Life.
Experts working with DNA, including DNA from animals like these hydrozoans, know that very little separates one species from the next. Experts know that Immortal Jellyfish cells act much like human stem cells. Cancer researchers and those studying longevity find this intriguing, particularly as the animals carry microRNA (miRNA) – minuscule strands of genetic material that function as gene expression regulators. The cells are capable of becoming skin cells, tentacle cells, or other cells; it all depends on what the body needs. Since cancers are marked by miRNA alterations, interest in these jellyfish and other hydrozoans is building.
Until more research is conducted, we won’t know for certain what implications the Immortal Jellyfish’s life cycle has for humans, if any. Even so, it is amazing to know that a little creature about the size of a tiny pinkie fingernail is able to rejuvenate itself so easily. More than mythological creatures, and because they are real, living beings, these creatures bestow hope – and that, in itself, is a wonderful thing.