Turritopsis nutricula is a tiny jellyfish, with a bell size of less than 1/4 inch. The diminutive creature would go unnoticed if not for its unique ability to regenerate its cells indefinitely. Found in the Atlantic Ocean, Turritopsis nutricula is capable of a form of biological immortality -- although it's not impossible to kill these jellyfish.
Defying the Typical Life Cycle
In the normal jellyfish life cycle, the animal is born, develops, lives out its reproductive stage and then moves toward death. But the unique hydrozoan species Turritopsis nutricula defies this typical life pattern. These animals have an unusual ability to revert back to a larval state even after living and reproducing as adults, only to develop again into adult-form jellyfish. Because each individual jellyfish is able to keep itself alive for an indefinite amount of time after it reaches sexual maturity, T. nutricula can achieve extremely large colonies. Originating in the Caribbean Sea, the immortal jellyfish has spread to coastal waters along the United States and even as far north as Europe. Scientists believe that the tiny jellyfish migrated via the ballast tanks of large ships, and that they may cause environmental problems in the future because of their rapidly growing numbers.
How the Immortal Jellyfish Reproduces
The immortal jellyfish begins its life as an egg. T. nutricula, like other hydrozoan jellyfish, are colonists. They spawn in large groups, the males releasing sperm into the water that fertilizes the females' released eggs. Fertilized eggs develop within the jellyfish's bell, then are deposited on the ocean substrate in large groups. The eggs hatch two days after they're deposited and begin life in the polyp stage. After about two weeks, the jellyfish has completed the polyp stage and is a sexually mature adult, fully capable of reverting back into a polyp if necessary. How long it takes for the polyp to develop into an adult jellyfish depends on water temperature -- the warmer the water, the faster the jellyfish develops into a medusa.
How the Immortal Jellyfish Gets Reborn
The immortal jellyfish is able to revert back to its polyp stage through transdifferentiation -- the ability of cells to morph into other cells. Other animals possess this ability, such as salamanders, geckos and sea stars, which can regenerate lost body parts. However, no other animal has been studied that can transdifferentiate its entire body like T. nutricula does. Transdifferentiation most often takes place after the medusa-form jellyfish has mated. The process begins with inversion of the medusa's bell. Then the jellyfish anchors itself to the ocean substrate. At that point the immortal jellyfish's cells fully transdifferentiate, resulting in a bloblike mass, which reforms into a jellyfish polyp. T. nutricula's cells can reconfigure into completely different structures, for instance a muscle cell can revert to a nerve cell.
T. Nutricula Can Die
It is possible for the immortal jellyfish to die. The ability to transfigure is possible only once the animal has reached the adult stage. So, a polyp that was never an adult lacks the ability to transdifferentiate its cells and save its own life. Also, destroying the animal's nerve center kills the immortal jellyfish. Without the nerve center, the signal to initiate transdifferentiation can't be sent throughout the animal's body. Meanwhile, the immortal jellyfish in its egg, polyp and medusa forms, is subject to predation by other animals. Because of their tiny size, T. nutricula is easy feeding for the vast number of filter feeders and small fish in the world's oceans. However, if left intact in a favorable environment, the immortal jellyfish could indefinitely continue its polyp-to-medusa-to-reproducing-adult-to-polyp-to-medusa cycle.
- Mother Nature Network: Immortal Jellyfish: Does It Really Live Forever?
- World Register of Marine Species: Turritopsis nutricula; McCrady, 1857
- Discover Magazine: The Curious Case of the Immortal Jellyfish
- National Institutes of Health: Transdifferentiation, Metaplasia and Tissue Regeneration
- Nature and Science: Turritopsis nutricula
- NA/AbleStock.com/Getty Images