Jellyfish

Jellyfish are found all over the world, from surface waters to the deep sea and have been in e xistence for at least 500 million years, making them the oldest multi-organ animal group. Don't be squeamish: find out more about these incredible invertebrates.

Jellyfish
image by Florian Olivo

Despite their name, jellyfish aren’t really a type of fish. Fish are vertebrates that live in water and breathe through their gills, while jellyfish are invertebrates, meaning they have no backbone and they absorb oxygen from water through membranes. They are a type of zooplankton (from the Greek word planktos, meaning to wander or drift) and have no brain, heart, bones or eyes. About 5% of jellyfish bodies are made of structural proteins, muscles, and nerve cells, while the remaining 95% is water. Human bodies, by comparison, are up to 60% water. They have a smooth, bag-like body and tentacles armed with tiny, stinging cells used to stun or paralyze their prey before eating it.

Jellyfish provide habitat for many juvenile fish in areas where there are not many places to hide. They protect the small fish from being eaten by predators with their stinging cells. Also, young crabs hitchhike on the top of jellyfish so they don’t have to swim.