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They're ancient animals -

Jellyfish are the oldest multicellular animals on the planet. Jellyfish were even around before the dinosaurs!

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They've been around for countless millennia -

Archaeologists have discovered jellyfish fossils in rocks that they believe to be more than 500 million years old.

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There's no fish in jellyfish -

Jellyfish may live in the water, but they aren't related to fish. They're invertebrates, in the same animal group as squid, sea urchins, and octopuses.

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They're mostly water -

Jellyfish are made of between 85% and 95% water. When they wash up on the shore, their bodies start to disappear as the water evaporates.

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They don't have brains -

Jellyfish don't have brains, hearts, or lungs. They don't need these vital organs, as they absorb oxygen through their thin 'skin' and simply respond to their environment using a network of nerves below the surface of the epidermis.

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That isn't to say that jellyfish aren't smart -

They might not have brains, but jellyfish aren't stupid. They're clearly very adaptable creatures that have survived countless major changes in their environment over the centuries.

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Climate change -

They're even adapting well to climate change.  Jellyfish continue to thrive despite rising ocean temperatures, ocean acidification, overfishing, and all the other factors that are endangering other forms of marine life.

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Jellyfish have been to space -

In fact, they're so adaptable that they even thrived in space! NASA started testing how well jellyfish adjust to space in the 1990s. They sent up thousands of baby jellyfish and examined them as they developed.

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They rely on gravity -

The reason this experiment was helpful is that humans and jellyfish are similar in that we both rely on gravity to orient ourselves, so their behavior can tell us how humans might fare in outer space.

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They adapted a little too well... -

As it turns out, the jellyfish born and raised in outer space developed to survive in a zero-gravity atmosphere and were no longer fit for life on Earth! It's likely that humans born in space would also grow up without the gravity sensors required to exist on Earth.

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They can be tiny... -

Jellyfish range in size drastically. Some are so tiny that they are almost invisible as they float around in the ocean, such as the Staurocladia and Eleutheria. They can be as small as 0.2 inches (0.5 cm).

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...or enormous! -

At the other end of the scale, you have the Nomura's jellyfish, which has a bell, as the head is known, of up to 6.5 feet (2 m). They can weigh up to 440 pounds (200 kg).

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They can have incredibly long tentacles -

Most of a jellyfish's impressive length usually comes from its tentacles. The Lion's mane jellyfish, for example, can have tentacles as long as 120 feet (37 m).

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Somehow, they never get tangled up -

Despite their many long undulating tentacles floating around in the currents, jellyfish never get tangled up or sting themselves. Their stingers only react to other species of jellyfish.

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Some jellyfish have teeth -

Jellyfish don't have many of the traditional features we associate with animals, like brains or lungs, but some of them do have teeth! Comb jellyfish have hundreds of rows of tiny cilia that act as teeth and can be used to tear apart their prey.

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And some have eyes! -

Some types of jellyfish have eyes. The box jellyfish, which is the most deadly kind, has 24 eyes, two of which are capable of seeing in color. It's believed to be one of the few creatures in the world with full 360-degree vision.

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Life cycle of the jellyfish -

Jellyfish cycle through several different stages. They begin as larvae, grow into polyps, then into baby jellyfish, and when they are mature, they reach the medusa stage. When we picture a jellyfish with its bell-like head and tentacles, it is a medusa jellyfish.

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Medusa -

The mature jellyfish is called medusa after the monstrous figure in Greek mythology. Medusa was a woman whose hair was made of snakes. It's easy to see how legends of her appearance were linked to jellyfish!

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There are thousands of species of jellyfish -

There are more than 2,000 species of jellyfish that have been discovered and named, but there are likely hundreds of thousands more.

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How many more? -

Scientists estimate there are actually as many as 300,000 species of jellyfish lying undiscovered in the ocean.

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Their life spans vary greatly -

Some of the tiniest jellyfish only live for a matter of days. The average jellyfish lives for approximately one year.

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Some jellyfish might be immortal -

While most jellyfish have a relatively short life span, there are a couple of rare species that may be immortal. Researchers have discovered that the Turritopsis dohrnii and the Turritopsis nutricula can cheat death. They are both known as "the immortal jellyfish."

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They behave like the mythological phoenix -

When they die, these species of jellyfish sink to the ocean floor and begin to decay. The cells then regenerate into polyps, which turn into new jellyfish, starting the life cycle all over again.

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A major scientific discovery -

The process is called cellular transdifferentiation and scientists say it's one of "the most amazing discoveries of our time.”

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They are highly effective predators -

They may be beautiful and miraculous in many ways, but it's important to remember that they are highly effective predators and can be deadly to humans. They paralyze their prey using the venom in their tentacles before eating them.

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How dangerous are they? -

Their microscopic barbed stingers usually cause instant pain when they come into contact with human skin. However, the real danger depends on the type of jellyfish and its venom. Some cause a full-body reaction that can be fatal, in rare cases.

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They don't want to hurt you -

Jellyfish usually float in the water doing their own thing. They don't go out of their way to attack, but will sting foreign bodies that come in contact with their stingers. If you're worried about swimming during jellyfish season (mid-spring through late summer), a wetsuit should do the trick.

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Don't do it! -

If you do get stung by a jellyfish, you should know that peeing on the area won't help! In fact, this supposed treatment might make it worse.

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Some jellyfish are edible -

The jellyfish that won't kill you might actually be edible. In countries like South Korea and Japan, they are a delicacy that can be eaten raw like sushi, fried until crunchy, or turned into a chewy candy.

Sources: (One Earth) (CBC) (Treehugger) (The Atlantic) (BBC Earth)

See also: Weird ways animals are eaten around the world

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