With no brains, no heart and no blood, it’s incredible to think that jellyfish have survived for more than 500 million years – even predating dinosaurs!

More than 100 species of jellyfish have been recorded along the Great Barrier Reef, including the notorious stinging blue bottles and box jellyfish. One of these, the infamous Irukandji jellyfish, is one of the smallest (roughly one cubic centimetre) and most venomous jellyfish in the world.

On a more positive note, as well as being a favourite food for the Reef’s marine turtles, large adult jellyfish are often accompanied by small fish which hide amongst their tentacles for protection.

And that’s just the beginning. Here are five fun facts about jellyfish you probably didn’t know.

1. Jellyfish are not actually fish! They’re gelatinous zooplankton (or for the scientifically-minded, invertebrates from the phylum Cnidaria).
2. Their bodies are made up of as much as 98% water – the ultimate camouflage for a marine creature!
3. They might not have a brain or heart, but some jellyfish can see. For instance, the box jellyfish has 24 ‘eyes’, two of which are capable of seeing in colour. It’s also believed that this animal's complicated array of visual sensors make it one of the few creatures in the world to have a full 360-degree view of its environment.
4. A group of jellyfish is not a school or a pod. It’s usually called a bloom or swarm, but is sometimes also called a ‘smack’.
5. Jellyfish have been to space. NASA first started sending jellyfish to space on board the Columbia space shuttle in the early 1990s to test how they might get along in a zero-gravity environment. Why? Because like people, jellyfish rely on specialised gravity-sensitive calcium crystals to orient themselves, so studying how jellyfish manage in space can reveal clues about how humans might also fare.