A jellyfish looks like a floating sac of jelly, and if you’ve ever seen one, you know how it got the jelly part of its name. But the fish part of the name is less deserved, for the jellyfish is not a fish at all.
Fish have skeletons, blood, and brains, but the jellyfish, like the sponge and the coral, has no skeleton, no blood, and no brain! It consists mostly of a sac-like stomach, a mouth, and long tentacles, which sting and capture its prey.
Some jellyfish are tiny, but others are over seven feet in diameter, with tentacles 120 feet long!