Life of the Immortal Jellyfish (Turritopsis nutricula)
The immortal jellyfish is the only confirmed example of an organism that can theoretically live forever. Studies in laboratory conditions have shown that injured adults can transform themselves back into their polyp stage of development. They are not true jellyfish (class Scyphozoa), instead belonging to the related Hydrozoa class.
Hydrozoan Life Cycle
When the egg and sperm of an adult meet, they form free-swimming larvae known as a Planula. This searches for a firm substrate to attach itself onto, and develops into a polyp.
During the polyp stage, the hydrozoan reproduces asexually. It forms Medusa buds, which detach from the polyp and develop into free swimming adults that resemble the conventional jellyfish.
Discovery of Immortality
In 1988, a young German marine-biology student, Christian Sommer, was conducting research on hydrozoans in the Italian city of Rapallo. Sommer gathered wild specimens and grew them in petri dishes to observe their reproductive habits. He observed that one species appeared to refuse to die, instead aging in reverse until it reached its polyp stage, when it started to grow again.
Fascinated by Sommer’s observations, several scientists in Genoa continued to study the species. In 1996, they published a paper titled “Reversing the Life Cycle”. Further studies since have revealed the Immortal Jellyfish’s rejuvenation process.
Reversing the Life Cycle
The process happens when an individual is injured or stressed. The cells of the jellyfish undergo a process known as cellular transdifferation, by which one type of body cell changes directly into another type of body cell.
In the first stage, the jellyfish sinks to the bottom, where its body folds on itself. The tentacles and bell degenerates until it resembles a gelatinous ball. Over the course of a few days, this ball forms an outer “shell”, continuing to develop stolons (root like structures). These stolons grow and develop into polyps, thus restoring the jellyfish to its early stages of development. The polyp can then continue the life cycle, forming more adult medusae.
This process has only been observed in the laboratory as encountering and capturing the whole process in the field is extremely unlikely. In the wild, an injured adult may be eaten before it can rejuvenate itself. It is also improbable that an individual can avoid predation and disease for successive generations to live forever.
Images: 1:Public Domain 2:© WoRMS for SMEBD 3: Calibro.edu
Information source: NYTimes