Jellyfish have been living at least for 500 million years. The smallest jellyfish is the Peculiar Creeping Jellyfish. If jellyfish are in a group its called a smack. A bloom is a huge group of jellyfish. Rising sea temperatures caused by climate change may also make jellyfish blooms. Lots of jellyfish are relatively better able to survive in warmer water and some jellyfish live in fresh water. Jellyfish do not have a brain. There is a chemical reaction that causes these creatures have light inside of them that is called bioluminescence this causes jellyfish to glow