Why are jellyfish clear?
A jellyfish has a protective skin, or "jelly bag," which is filled with a jelly-like secretion that is 94 percent water. The jellyfish doesn't have a heart, a brain, or bones! The jelly is held together by muscle fibers that lace through it. The jellyfish has a hollow stomach, connected directly to its mouth. The mouth is the only opening on the body, so the food goes in, and the waste passes out there as well. Jellyfish also use their mouths to swim. They let the water come in and fill up their stomachs; when they pump it out, it propels them.