A jellyfish's body is made up mainly of water, along with a jelly-like substance called mesoglea, tentacles, a mouth and a thin layer of skin. Its body is around 90 percent water and its skin is only one cell thick.
The jellyfish does not have a brain, heart or any other organs. In fact, jellyfish don't even have a head. Instead of a nervous system, they have a movable network of nerves that is positioned along their epidermis, which is called a "nerve net." Jellyfish have light-sensitive organs called ocelli, which identifies light but not images. Box jellyfish have more superior eyes, some of which can identify color.
The jellyfish's tentacles are used to sting and catch prey. The sting of a box jellyfish's tentacles is so powerful that it can kill a human being in minutes.