Jellyfish are one of the most fascinating and mysterious creatures in the marine ecosystem. They belong to the phylum Cnidaria, represented by multicellular organisms with the presence of cnida. The mysterious image they evoke is due to the fact that very little is known about these animals. There are several characteristics of jellyfish that pique human curiosity, such as their unique shape, their movement, their bioluminescence or their venom. However, their life cycle has always been the epicenter of research to better understand these animals.
Some species, such as Turritopsis dohrnii, are considered "immortal" due to their unique life cycle. This species, also known as the Benjamin Button jellyfish, is one of the few known animals that can regenerate and the only species of jellyfish with an indefinite lifespan. It is small, measuring around 4.5 millimeters in width and height, and was first described in 1883 in the Mediterranean Sea near Japan. These jellyfish are carnivorous, feeding on prey such as fish eggs, plankton and small molluscs. But they are also hunted by predators such as larger jellyfish, sea anemones, tuna, sharks, sea turtles and penguins.
Its life cycle is very similar to that of other jellyfish, which also alternate generations (metagenesis). It has both a sexual and an asexual phase. The cycle begins with a fertilized egg, from which hatches a tiny, ciliated larva that attaches itself to a substrate in the sea. It then grows into a polyp. From this polyp, young male or female jellyfish sprout after a process of strobilization. These jellyfish develop into adult jellyfish capable of sexual reproduction and the cycle begins again with a new individual generated from this
reproduction. However, in the case of T. dohrnii it is different, because it is capable of doing
the reverse path of the cycle, that is, it is capable of even after becoming an adult jellyfish,
returning to being a polyp, and it can do this indefinitely. In this way, it can restart its life cycle whenever necessary. For this reason, it is considered an "immortal" individual, since it is not capable of dying of aging. However, it is important to note that it is not truly immortal, since it can be killed by predators and in ways other than aging.
The possible secret to this jellyfish's longevity is its ability to transdifferentiate. This means that the adult cells of this jellyfish, already specialized in a certain function, are capable of turning back into stem cells, which in turn can transform into any other. This ability allows this species not only to revert from an adult to a polyp state, but also for cells in its body that are damaged or diseased to become healthy again. It is believed that in situations of stress or injury, this species reverts to the previous state of the cycle as a defense mechanism.
One point of attention in this process of turning back into a polyp is that each time it does this, new genetically identical individuals can be generated by returning to the asexual
phase. This is worrying because they have a wide distribution around the world, but the
population level of this species is unknown; it is only known that they have the potential to
increase their population in a short space of time due to this ability. The risk and ecological
impact of this population increase have not yet been measured.
Despite this risk, most studies are focused on trying to understand the immortality of T.
dohrnii, mainly with a view to pharmaceutical and medical applications. However, there is still
a long way to go to understand how these modifications actually occur. So until then, these
animals will remain fascinating and mysterious.
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