The immortal jellyfish or Turritopsis dohrnii, is a species of small jellyfish which is mostly found in the Mediterranean Sea and in the waters of Japan. It’s unique as it shows a certain form of “immortality”.It is the only known case of an animal skilled of reverting fully to a sexually immature, colonial stage after having accomplished sexual maturity as a solitary stage.
Like most other hydrozoans, Turritopsis begin their life as freeswimming tiny larva known as planula. As aplanula calm down, it gives rise to a colony of polyps that are attached to the seafloor. Jellyfish,also known as medusae, then bud off these polyps and keep on their life in a freeswimming form, ultimately becoming sexually mature. All the polyps and jellyfish arising from a single planula are genetically identical clones. If a T. dohrnii jellyfish is exposed to ecological stress or physical assault, or is sick or old, it can relapse to the polyp stage, forming a new polyp colony. It does this through the cell development process of cell transdifferentiation, which alters the differentiated state of the cells and transforms them into new types of cells.
Theoretically, this process can go on for ever, effectively rendering the jellyfish biologically immortal, although, in nature, mostTurritopsis are likely to surrender to predation or disease in the medusa stage, without returning to the polyp form.
The name jellyfish has been in use since 1796. It has usually also been applied to other animals sharing a superficial resemblance, for example ctenophores were included as “jellyfishes”. Even some scientists comprise the phylum ctenophora when they are referring to jellyfish. Other scientists prefer to use the more allencompassing term gelatinous zooplankton, when referring to these, together with other spongy-bodied animals in the water column.
The medusa of Turritopsis dohrnii is bellshaped,with a maximum diameter of about 4.5 millimetres and is about as tall as it’s width. The jelly in the walls of the bell is uniformly thin, except for some thickening at the apex. The relatively large stomach is bright red and has a cross-sectionally cruciform shape. Young specimens 1 mm in diameter have only eight tentacles evenly spaced out along the edge, while adult specimens have 8090 tentacles. Jellyfish is living frrely in the plankton.
Dohrnii also has a bottomliving polyp structure, or hydroid, which consists of stolons that run along the substrate, and upright branches with feeding polyps that can produce medusa buds. These polyps develop over a few days into tiny 1 mm medusae, which are liberated and swim free from the parent hydroid colony.
Turritopsis is believed to have started off in the Caribbean but has distributed all over the world, and has speciated into several populations that are easy to differentiate morphologically, but whose species distinctions have recently been verified by a study and comparison of mitochondrial ribosomal gene sequences. Turritopsis are found in moderate to tropical regions in all of the world’s oceans. Turritopsis is believed to be extending across the world as ships are discharging ballast water in ports. Since the species is immortal, the number of individuals could be rising rapidly.“We are looking at a worldwide silent invasion”, said Smithsonian Tropical Marine Institute scientist Dr. Maria Pia Miglietta.
The eggs build up in gonads of female medusae, which are situated in the walls of the manubrium (stomach). Mature eggs are presumably spawned and fertilized in the sea by sperm produced and released by male medusae, as is the case for most hydromedusae, although the related species Turritopsis rubra seems to hold fertilized eggs until the planula stage. Fertilized eggs develop into planula larvae, which settle onto the sea floor (or even the rich marine communities that live on floating docks), and develop into polyp colonies (hydroids). The hydroids bud new jellyfishes,which are released at about 1 mm in size and then grow up and feed in the plankton, becoming sexually mature after a few weeks (the exact time duration depends on the ocean temperature; at 20 °C (68 °F) it is 25 to 30 days and at 22 °C (72 °F) it is 18 to 22 days).
Most jellyfish species have a reasonably fixed life span. It is different by species from hours to many months. The medusa of Turritopsis dohrnii is the only form known to have developed the ability to come back to a polyp state, by a specific transformation process that requires the presence of certain cell types.It is revealed from Certain laboratory experiments, that all stages of the medusae, from newly released to fully mature individuals, can transform back to polyps. The transforming medusa is characterized first by fall back of the bell and tentacles, with the subsequent growth of a perisarc sheet and stolons, and finally feeding polyps. Polyps further multiply by growing added stolons, branches and then polyps, to structure colonial hydroids. This ability to reverse the life cycle is probably unique in the animal kingdom, and allows the jellyfish to bypass death, causing Turritopsis dohrnii potentially biologically immortal. Laboratory Studies showed that 100% of specimens could revert to the polyp stage, but so far the process has not been detected in nature, in part because the process is quite fast and field inspections at the right moment in time are unlikely. In spite of this notable ability, most Turritopsis medusae are likely to fall victim to the general hazardss of life as plankton, including being eaten up by other animals, or surrendering to disease.
The Turritopsis dohrnii’s cell development method of cell-transdifferentiation has inspired scientists to find a way to makestem cells by using this process for renewing damaged or dead tissue in humans.