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16 Interesting Facts about Jellyfish

Last Reviewed and Updated on June 26, 2022

Most people avoid them when they see them in water and it’s for a good reason, jellyfish sting, and while most stings aren’t deadly, they are painful. That jellyfish fact aside, these animals are fascinating and mesmerizing. 

One of them might even be immortal… Now if that’s not something to be amazed about we don’t know what is.

1. They mostly live in saltwater

True jellyfish can only be found living in saltwater, however animals with a similar appearance, hydrozoans, can be found in freshwater.

2. A jellyfish is not a fish

Their name might suggest they are a part of the fish family but they are not, and the only thing they really have in common with fish is their habitat and ability to move in the water.

Fish are vertebrates (have a backbone) and jellyfish are invertebrates (don’t have a backbone),

3. A group of jellyfish is called a smack

A smack of jellyfish. Has a ring to it. A group of jellyfish can also be called a swarm or a bloom. They can be solitary, but most do live in groups so these terms are worth remembering.

4. Jellyfish by itself is not a species, it’s a term used to describe a part of this animals life cycle

Jellyfish or medusa is a phase of the life cycle of some members of the Medusozoa. Other parts of the cycle include the egg, the planula larva, polyp, strobila, and ephyra. 

5. Fossils of jellyfish are rare

Since jellyfish have no bones or other hard parts in their body, fossils of them are rare.

What we see in jellyfish fossils are actually their prints and not the organism itself.

6. Their mouths are also their anus

They technically don’t have an anus but will excrete waste through their mouth. But this is also not the case for all jellyfish, the warty comb jelly can create an anus when it needs one. Hands down one of the most interesting facts about jellyfish and the weirdest.

7. Jellyfish don’t have lungs

Or brains as we know them, or a heart. They still need oxygen though and they get it through their thin skin. One of the freakiest facts about jellyfish, however, they are far from being the only species lacking organs we take for granted.

Learn what are some other animals without brains.

8. They come in many sizes

Smallest known jellyfish measures about a millimeter and the largest known jellyfish, Lion’s mane jellyfish measures about 6 ft and 7 inches / 2 m.

9. Jellyfish are capable of reproducing asexually

We already mentioned the “normal” life cycle of these animals, consisting of eggs and fertilization. But it’s not that simple, the medusa/jellyfish stage reproduces sexually, while the polyp stage of this animal’s life cycle is capable of reproducing asexually by cloning themselves.

10. A species Turritopsis dohrnii might be immortal

This has to be one of the coolest facts about jellyfish, even though it currently applies to one species only. This species is also called the immortal jellyfish and they got named after their unique ability to switch back and forth between the different stages, this jellyfish for example can revert back to the polyp stage if stressed or damaged. In theory, this makes them immortal.

11. They are generally carnivorous

They feed on planktonic organisms, small fish, fish eggs, larvae, and other small creatures they can find.

12. Some jellyfish have partnerships with certain fish

Juvenile fish of some fish species will seek protection between the tentacles of jellyfish.

13. Some are bioluminescent

Many species of jellyfish are bioluminescent, meaning they produce light, some more than others. The main purpose of their bioluminescence is to deter predators and the most common glow color is blue, or blue-green.

14. They can sting you, stings ranging from mild, to painful and even deadly

Some sting mildly, and some don’t sting at all. But some can kill you. Sea wasp (Chironex fleckeri) is one of the most poisonous jellyfish out there and if the sting is left untreated it can kill you.

15. Jellyfish caused a power blackout in the Philippines in 1999

They have sadly been sucked in the water intake of the power plant, clogging things up and causing the blackout.

16. They are eaten in some parts of the world

They are commonly found on the menu in some parts of the world.

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