Immortal jelly

Turritopsis dohrnii, commonly known as the immortal jellyfish, is a species of small, biologically immortal Medusozoa (jellyfish) found worldwide in temperate to tropic waters. It is one of the few known cases of an animal capable of completely reverting to a sexually immature, sedentary polyps colonial stage after having reached sexual maturity as a solitary individual.

Like most other hydrozoans, T. dohrnii begin their lives as tiny, free-swimming larvae known as planulae. As a planula settles down, it gives rise to a colony of polyps that are attached to the sea floor. All the polyps and medusa arising from a single planula are clones. The polyps form into an extensively branched form, which is not commonly seen in most jellyfish. Jellyfish, also known as medusae, then bud off these polyps and continue their life in a free-swimming form, eventually becoming sexually mature. When sexually mature, they are known to prey on other jellyfish species at a rapid pace. If the T. dohrnii jellyfish is exposed to environmental stress, physical assault, or is sick or old, it can revert to the polyp stage, forming a new polyp colony. It does this through the cell development process of transdifferentiation, which alters the differentiated state of the cells and transforms them into new types of cells.

Theoretically, this process can go on indefinitely, effectively rendering the jellyfish biologically immortal, although in practice individuals can still die. In nature, most Turritopsis dohrnii are likely to succumb to predation or disease in the medusa stage without reverting to the polyp form.

The capability of biological immortality with no maximum lifespan makes T. dohrnii an important target of basic biological aging and pharmaceutical research.

From the Wikipedia article “Turritopsis dohrnii” (en.wikipedia.org/w/index.php?title=Turritopsis_dohrnii&oldid=1383429768), by Wikipedia contributors, licensed under CC BY-SA 4.0 (creativecommons.org/licenses/by-sa/4.0). This block is kept separate from our own text.