the Legacy continues…………………….
Gregory R. Mann, Ph.D. {ret.}

Immortal Sea Jelly

“Turritopsis dohrnii”

Right from the start, the proper scientific name for these animals is “Sea Jelly” not “Jellyfish”. The very small Immortal Sea Jelly is found in the Mediterranean Sea and in the waters of Japan. It’s one thing to survive in harsh environments, but quite another to hit the reset button when faced with an imminent threat. Only one animal is known to have this remarkable ability. The Immortal Sea Jelly was first discovered in the 1880’s in the Mediterranean Sea. Like all sea jellies, it begins life as a larva called a planula, which develops from a fertilized egg. A planula swims at first, then settles on the sea floor and grows into a cylindrical colony of polyps. Fully grown, the Immortal Sea Jelly is only about 4.5 millimeters (0.18 inches) across. A bright-red stomach is visible in the middle of its transparent bell, and the edges are lined with up to 90 white tentacles. These tiny, transparent creatures have an extraordinary survival skill, though. In response to physical damage or even starvation, they take a leap back in their development process, transforming back into a polyp. In a process that looks remarkably like immortality, the born-again polyp colony eventually buds and releases medusae that are genetically identical to the injured adult. In fact, since this phenomenon was first observed in the 1990’s, the species has come to be called “the Immortal Sea Jelly.” The cellular mechanism behind it, a rare process known as transdifferentiation is of particular interest to scientists for its potential applications in medicine. By undergoing transdifferentiation, an adult cell, one that is specialized for a particular tissue, can become an entirely different type of specialized cell. It’s an efficient way of cell recycling and an important area of study in stem cell research that could help scientists replace cells that have been damaged by disease.

This jelly is not only an extraordinary survivor but also an increasingly aggressive invader. Marine species have long been known to hitch rides around the world in the ballasts of ships. Researchers have recently identified the Immortal Sea Jelly as an “excellent hitchhiker” particularly well-suited to surviving long trips on cargo ships suspecting the sea jellies are hitching rides inside long-distance cargo ships. The creatures are likely traveling in the ship’s ballast water—water sucked into and pumped out of ships to provide stability. Meanwhile, polyps could be attaching to the hulls. The Immortal Sea Jelly’s cells are often completely transformed in the process. Muscle cells can become nerve cells or even sperm or eggs. Through asexual reproduction, the resulting polyp colony can spawn hundreds of genetically identical sea jellies—near perfect copies of the original adult. This unique approach to hardship may be helping Turritopsis dohrnii spread throughout the world’s oceans. For reasons still mysterious, the Immortal Sea Jelly takes on slightly different forms as it spreads. Swarms living in tropical waters typically have only 8 tentacles, while those in temperate regions can have 24 or more tentacles. Another mystery is how the sea jellies achieve their remarkable age reversal. Researchers speculate that the creatures have very effective cellular repair mechanisms that allow them to age without incurring the usual ravages of time.

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