Immortal jellyfish facts for kids

Quick facts for kids Immortal jellyfish
Turritopsis dohrnii medusa
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Anthoathecata
Family:	Oceaniidae
Genus:	Turritopsis
Species:	T. dohrnii
Binomial name
Turritopsis dohrnii (Weismann, 1883)
Script error: The function "autoWithCaption" does not exist.
Synonyms
Cytaeis polystyla Will, 1844 Dendroclava dohrnii Weismann, 1883

Script error: No such module "Check for conflicting parameters".

The Turritopsis dohrnii, often called the immortal jellyfish, is a tiny type of jellyfish. It lives in warm and mild oceans all around the world. This amazing creature is special because it can actually turn back into a younger stage of its life after it has grown up. It's one of the only animals known to do this!

Like many other jellyfish, T. dohrnii starts as a tiny larva called a planula. This larva swims freely until it finds a place to settle. Then, it grows into a group of small polyps attached to the sea floor. All the polyps and jellyfish that come from one planula are clones, meaning they are exact copies. These polyps grow into a branched shape, which is unusual for jellyfish. Later, small jellyfish, also called medusae, bud off from these polyps. They swim freely and grow up. If a T. dohrnii jellyfish gets stressed, hurt, sick, or old, it can change back into a polyp. This happens because its cells can change their jobs, a process called transdifferentiation. This allows it to form a new polyp colony.

In theory, this process could go on forever, making the jellyfish biologically immortal. This means it doesn't die of old age. However, in the wild, most of these jellyfish are still eaten by other animals or get sick. So, they don't always get to use their special ability.

Because it can live forever without aging, the immortal jellyfish is very important to scientists. They study it to learn more about aging and to help develop new medicines.

Discovering the Immortal Jellyfish

Scientists first named this jellyfish in 1883. They honored Anton Dohrn, who started a famous marine research station in Naples, Italy. For a long time, scientists thought this jellyfish was the same as another species, T. nutricula. But in 2006, new studies showed they were different species. It's still a mystery if a related jellyfish, T. rubra, can also turn back into a polyp.

How it Looks

The immortal jellyfish has a bell shape. It is very small, only about 4.5 millimeters (0.18 inches) wide. That's about the size of your pinky fingernail! Its stomach is bright red and shaped like a cross. Young jellyfish have only eight tentacles around their edge. But adult jellyfish can have 80 to 90 tentacles. These tiny jellyfish float freely in the ocean's plankton. They also have a special network of nerve cells in their bell.

The Turritopsis dohrnii also has a polyp form. These polyps live on the sea floor. They look like small plants with branches. These branches have feeding polyps that can create new jellyfish buds. These buds grow into tiny 1-millimeter jellyfish in just a few days. Then, they swim away from the polyp colony.

Where it Lives and Travels

Scientists think the immortal jellyfish first came from the Pacific Ocean. But now, you can find it in all the world's oceans, from warm tropical areas to cooler regions. It has spread around the globe, possibly by traveling in the ballast water of ships. Ballast water is water that ships take in to stay balanced, and then release later.

This spread has been called a "silent invasion" by scientists. This is because the jellyfish are so tiny and don't cause harm. They are also very tough. They can survive in harsh conditions, even without much food. Their ability to turn back into a cluster of cells helps them survive and spread. This makes them very good at living in many different places.

The Amazing Life Cycle

The life of an immortal jellyfish starts with tiny eggs. These eggs grow inside the female jellyfish. When they are ready, the eggs are released into the sea. There, they are fertilized by sperm from male jellyfish. These fertilized eggs then grow into tiny swimming larvae called planulae.

The planulae eventually settle down. They attach to the sea floor or even to floating docks. Once settled, they grow into colonies of polyps, which look like small plants. These polyps then create new, tiny jellyfish. These new jellyfish are about one millimeter long when they are released. They swim and feed in the ocean, growing up in a few weeks. How fast they grow depends on the water temperature. For example, at 20°C (68°F), it takes about 25 to 30 days. These jellyfish can live in water temperatures between 14°C and 25°C (57°F and 77°F).

The Secret of Immortality

Most jellyfish live for a set amount of time, from a few hours to several months. But the Turritopsis dohrnii is different. It is the only known jellyfish that can turn back into its polyp stage. This special change needs certain types of cells from its bell and internal systems.

Scientists have done experiments to understand this. They found that jellyfish of all ages can change back into polyps. This happens if they are starving, if the water temperature changes suddenly, or if the water becomes less salty. Even if they are hurt, they can transform. The jellyfish's bell and tentacles first start to break down. Younger jellyfish then form a small cyst before becoming polyps. Older jellyfish can sometimes skip the cyst stage and go straight to forming polyps. These new polyps can then grow and create more polyps, starting a new colony. In experiments, they even did this without any stress or injury!

This ability to reverse its life cycle is truly unique among all animals. It means the jellyfish can avoid dying of old age. This makes Turritopsis dohrnii potentially biologically immortal. Scientists haven't seen this happen often in the wild. This is because the change happens very quickly. Also, it's hard to be watching at just the right moment. Even with this power, most jellyfish in nature are still eaten by predators or get sick.

This jellyfish has special ways to keep its cells young. It uses unique processes to maintain parts of its DNA called telomeres. This helps it reset its cellular age when it reverses its life cycle.

Scientists are very interested in how these jellyfish's cells change their jobs. They hope to learn from this process. This could help them find ways to repair damaged body parts in humans.

What it Eats and Who Eats It

Its Favorite Foods

The immortal jellyfish is a carnivore, meaning it eats other animals. It mainly feeds on tiny ocean creatures called zooplankton. Its diet also includes fish eggs and small mollusks. The jellyfish uses its mouth to eat food and also to get rid of waste. It hunts by letting its tentacles drift in the water. These tentacles have stinging cells called nematocysts. They sting its prey, then pull the food to its mouth. The jellyfish can also use its bell to catch food. As it swims, its bell expands, pulling water and tiny prey closer to its tentacles.

Who are its Predators?

Other jellyfish are the most common predators of Turritopsis dohrnii. But many other animals also eat them. These include sea anemones, tuna, sharks, swordfish, sea turtles, and penguins. Many animals eat jellyfish because they are mostly water. They are made of three simple layers: an outer layer, a middle jelly-like layer, and an inner layer.

Where Does it Live?

The immortal jellyfish was first found in the Mediterranean Sea. But now it lives all over the world. You can find it in warm and mild ocean waters. They often live in marinas or docks. They can also be found on the bottoms of boats and on the ocean floor. They prefer water with a certain amount of saltiness, usually between 18 and 40 PSU (Practical Salinity Units).

Keeping Them in Labs

It is quite hard to keep T. dohrnii alive in a lab. Only one scientist, Shin Kubota from Kyoto University in Japan, has managed to keep a group of them for a long time. He has to check their food every day to make sure they are eating well.

Kubota once reported that his jellyfish colony went through its life cycle reversal 11 times in two years. He often talks about his immortal jellyfish on Japanese TV. He has even recorded songs about them, which he sometimes sings at the end of his science presentations!

See also

In Spanish: Medusa inmortal para niños

• Hydra – another kind of animal that is also said to be immortal