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Animal fun facts

10 Cool things you didn’t know about jellyfish

Published on November 03, 2016 | Last Updated December 01, 2022
A purple jellyfish.

1. Jellyfish are the oldest multicellular animals on the planet

A white jellyfish with spots all over it.

Scientists have discovered jellyfish fossil snapshots in rocks believed to be more than 500 million years old. That makes them even older than dinosaurs!

2. Jellyfish don’t have brains

An orange jellyfish with long tentacles.

They don’t have a heart, lungs or a brain either! So how does a jellyfish live without these vital organs?

Their skin is so thin that they can absorb oxygen right through it, so they don’t need lungs. They don’t have any blood so they don’t need a heart to pump it. And they respond to the changes in their environment around them using signals from a nerve net just below their epidermis — the outer layer of skin. It is sensitive to touch, so they don’t need a brain to process complex thoughts.

3. A jellyfish is called a Medusa

A multi-colour jellyfish with very short tentacles.

(Photo by Ihhs licensed CC BY-NC 2.0)

Jellyfish often look like a bell with tentacles all around the edge or hanging off the bottom. The shape of this bell is called a medusa because it looks like the evil Medusa in Greek mythology.

She was a woman who had offended the goddess Athena. Athena then changed Medusa's hair into snakes and made her face so hideous it turned people into stone. Medusa is also the word for jellyfish in many other languages including Greek, Hebrew and French.

4. Jellyfish can clone themselves

Little pink spotted jellyfish swimming together in a group.

(Photo by Yosuke Shizimu licensed CC BY-SA 2.0)

Imagine if you could just split yourself in half and create two of you? If you cut a jellyfish in half, the pieces of the jellyfish can regenerate and turn into two new jellies.

5. Some jellyfish have teeth

A white cone-shaped jellyfish with a large mouth.

(Photo: T3 Media/Nat Geo)

The beroid comb jellyfish has hundreds of rows of teeth. They are made of tiny hairs that can pierce, tear and pull their prey into their stomachs.

6. Jellyfish have gone into space

A small see-through jellyfish with long wispy tentacles.

(Photo: Howard Hall)

In 1991, moonfish jellyfish travelled into outer space on the Space Shuttle Columbia. Scientists wanted to examine how microgravity affected them. The jellyfish multiplied in space. When they came back to Earth, the scientists discovered that the space-born jellyfish couldn't figure out how to deal with gravity.

7. Jellyfish never get tangled

A large orange jellyfish with long bushy tentacles.

Even though some jellyfish have very long tentacles, they never get tangled up or sting them. That’s because the tentacles are very slippery and only sting other species of jellyfish.

8. Jellyfish can have super long tentacles

A group of orange jellyfish with tentacles at least five times longer than their bodies.

(CC0 Public Domain)

The lion’s mane jellyfish is the world’s largest jellyfish species. It can have tentacles that are over 27 meters long — longer than the size of the blue whale which is the biggest mammal in the world!

9. Jellyfish groups have a really awesome name

A bunch of little jellyfish underwater.

You might think that a gaggle of geese, a murder of crows or a clowder of cats sounds interesting. But jellyfish groups have even better names. A group of jellyfish — which can include up to 300,000 of them — is called a bloom, a swarm or a smack.

10. There’s not much to a jellyfish

A blue jellyfish lying on the sand.

(Photo by Kelly Hunter licensed CC BY 2.0)

Jellyfish are between 85 per cent and 98 per cent water. If they wash up on the beach they’ll almost disappear as their water evaporates.

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