All About Jellyfish

They float through the sea - without a brain and without a heart, but with plenty of tentacles and stinging cells!

All About Jellyfish All About Jellyfish - Photos (TL-BR): abcphotosystem, Shutterstock, Humberto Ramirez, Damsea/Shutterstock

What Are Jellyfish?

Jellyfish are invertebrate marine animals that belong to the phylum Cnidaria. They seem to drift weightlessly through the water and are among the oldest creatures on Earth. The most well-known are the umbrella jellyfish, recognized for their unique body shape and tentacles. Jellyfish live freely in the ocean and can be found in all oceans – both at the surface and in great depths.

Main Characteristics of Jellyfish

1. Jelly-Like Body

Jellyfish are composed of about 98% water and lack a solid body structure, instead consisting of a gelatinous substance – they are essentially like small floating jelly desserts. Most are transparent.

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2. Tentacles With Stinging Cells

Most jellyfish have tentacles that they use to catch prey and defend themselves against enemies. Their tentacles have a superpower: stinging cells. Upon contact, tiny whip-like threads snap out from the cells, releasing a stinging venom.

3. Simple Body Structure, But Remarkable Abilities

Jellyfish do not have a brain or a heart, but possess a simple nervous system. Nevertheless, they respond to their environment and can move purposefully. But that's not all: they can remember the past, rejuvenate themselves (!), suffer from sleep deprivation, or merge with other jellyfish to form a new organism.

Jellyfish Family Tree

Amazing Facts About Jellyfish

There are 2,000-3,000 species of jellyfish, around 200 of which are true jellyfish.
Jellyfish only spend part of their lives swimming freely. Before they are fully grown, they're sessile for some time. In this state, they're called polyps.
Jellyfish are carnivores. They feed on the smallest creatures, zooplankton, crustaceans and other jellyfish.
They live all over the world, in warm and cold seas and in freshwater.
The largest is the lion's mane jellyfish. It lives in the Atlantic. Its bell grows well over six feet (2 meters) in diameter, its tentacles measure over 100 feet (30 meters) in length and it weighs up to one ton.
The smallest is the Irukandji jellyfish, which is native to Australia. Its bell measures only one inch (1-2.5 cm).
The most poisonous jellyfish is the sea wasp. A sting can cause death within 5-20 minutes. She lives on the coast of Australia.
The jellyfish Turritopsis dohrnii can rejuvenate itself and therefore is said to be "immortal".