An immortal jellyfish

Christian Sommer, a German student of marine biology, spending the summer of 1988 on the Italian Riviera, dived daily at the foot of the Portofino cliffs and surveyed the seabed, looking for hydrozoa that he caught with plankton nets. Among the many organisms he collected was a tiny, poorly researched species known to biologists as Turritopsis dohrnii.

immortal-jellyfish4It is barely 5 mm in size and with tentacles not thicker than hair, so finely contoured that under a microscope it looks like a drawing. In warmer water its transparent-white body becomes a bright red-purple color. Sommer kept his specimens in stone vessels observing them daily and after a few days noticed their very unusual way of reproduction. When they reach the peak of maturity, adults do not die, but return to their earliest stage of development to begin the life cycle again.

Sommer was confused by his discovery and did not immediately understand its significance.

However, several biologists from Genoa, fascinated by Sommer’s discovery, continued to study the species and in 1996 published a text entitled Reversing the Life Cycle. In it, they described how this species of jellyfish – even at any stage of its development – can transform back into a polyp, which is otherwise the first stage of life of this organism, thus avoiding death.

It could have been expected that this unusual discovery would cause a great storm among biologists, but it did not happen. The publication Reversing the Life Cycle has hardly been recorded outside of academic circles. In the meantime, further progress has been made in the research.

immortal jellyfishToday it is known that in Turritopsis the trigger for rejuvenation is physical danger, injury or the like, but the same happens when the jellyfish grows old or becomes ill. We also know that during rejuvenation, cell transdifferentiation takes place – an unusual process in which one type of cell transforms into another: a skin cell into a nerve cell, for example, as in human stem cells.

Furthermore, it was observed that the habitat of the species also expanded significantly. In addition to the Mediterranean, new colonies have been recorded along the coasts of Panama, Florida, Japan, and Spain, and are transmitted by the ballast waters of cargo ships. However, it is still unknown how this jellyfish can “age in the opposite direction”. The only rational conclusion is that it is because her body is composed almost exclusively of stem cells.

Research on this phenomenon is progressing slowly because there are a small number of experts in the world who are dedicated to the study of very small organisms, and specialists in hydroids are extremely rare. The second reason is that this order is extremely difficult to cultivate in the laboratory, and therefore to study. They require careful supervision and a lot of repetitive, tedious work. Even then, it will reproduce only under certain favorable circumstances, most of which are still unknown to biologists.

So far, only one scientist has succeeded, the Japanese professor Shin Kubota, who, after a full fifteen years of careful study, has given the most complete description of Turritopsis.

immortal jellyfishLike most hydrozoa, Turritopsis dohrnii goes through two main life stages: the polyp stage and the jellyfish stage. The polyp resembles a twig of dill with a spindle-shaped branch that forks and branches, ending in buds. When these buds swell, not flowers but jellyfish sprout from them. The bell-shaped hat from which the tentacles originate is similar to other so-called true jellyfish (skifomedusa), sea hats that belong to a different taxonomic group Scyphozoa that spends almost its entire life in this form. Hydrozoa, on the contrary, while in the life stage of jellyfish, live quite a short time. Adult true jellyfish produce eggs and sperm, from which larvae are formed which then form new polyps. After spawning, jellyfish die. The Turritopsis jellyfish sinks to the sea floor where its body is drawn into itself, corresponding to the jellyfish’s fetal stage. The cap resorbs its tentacles and then further degenerates until it becomes a gelatinous lump, resembling an amoeba. Over the course of a few days, this lump forms an outer shell. Then something like roots comes out of these tubers, which fixes them to the base. The tubers lengthen and become a polyp. A new polyp gives birth to new jellyfish and the process begins again. If a jellyfish does not suffer from a predator, its recovery, it seems, can go on indefinitely.

If we consider gene transfer to be immortality, then Turritopsis jellyfish can be called immortal. However, the newly formed cells are no longer the same, they have changed. And although the cells themselves can be considered “eternal”, this does not apply to the organism.

After that discovery, we can only wonder how many more puzzles our planet hides.

The appearance of a jellyfish resembles a bell, umbrella or hat, and less often a disk. The rim of a jellyfish may have a pleated border called a velum which serves as one of the main features by which skifomais are distinguished from hydromedusae.

The body of a jellyfish is made up of two layers of cells:

ectoderm, outer part, i
endoderm, inner part.

Between these two layers there is a gelatinous mass, the so-called mesoglea. It is a mass in which there are no cells and it connects these two layers, and at the same time gives them a certain strength. Inside is a cavity with only one opening that is both oral and anal. Around this opening is a series of tentacles, which is repeated on the perimeter of the jellyfish’s body.

Both the outer and inner layers of the jellyfish’s body are made up of epithelial-muscle cells, which are not true epithelial but also true muscle cells, and play the role of both. They consist of an enlarged part that has the role of an epithelial part, and an elongated part with the role of a muscle fiber.

Contraction of the muscle fibers of the outer layer causes elongation and shortening of the body and tentacles, while contractions of the inner layer causes contraction and expansion of the body. These movements are enough for them to move floating in the water, with the convex side facing in the direction of movement. In doing so, they move obliquely upwards, after which they are allowed to sink calmly downwards. Moving in this way, they reach a speed of about nine km / h.

In jellyfish, the nervous system appears for the first time in its simplest form. This is the so-called a “reticular nervous system” composed of star-shaped nerve cells, which are interconnected in a network. When a jellyfish is touched by one tentacles, the whole body convulses because the stimulus is transmitted through the net throughout the body.

Most jellyfish have long tentacles that are “equipped” with glowing cells. They are used for hunting, but also for defense. Glow cells secrete toxic contents. If Cnidrocil, the extension of the glow cell, is touched, the glow plug bursts and, at a pressure of 150 bar, ejects the filament, which has a harpoon end at its end. At the same time, in that way, it transfers the poison contained in the glow cell into the tissue that touched it. This is one of the fastest reactions known in the entire animal world. When the venom is expelled, the jellyfish discards the used glow cocoon, and builds a new one.

Giant jellyfish, such as Stomolophus nomurai, can reach a hat diameter of more than 2 meters and a weight of over 200 kg. But the body of a jellyfish contains as much as 99% water.

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