No brain, No blood, No Nervous System.
Jellyfish are boneless animals that are found in both the deep and shallow oceans of the world. They drift at the mercy of the currents, often accumulating in sheltered bays and estuaries. Despite the name, jellyfish are not actually fish, but form a group of their own. The body of the jellyfish is bell shaped and made up of a non-living jellylike substance. This jelly is surrounded by a layer of skin that is just one cell thick. The body of the jellyfish is made up of 90% water.
Jellyfish have no brain, no blood, and no nervous system. However, they have eyes. They also have tentacles around their mouths that vary in length depending on the species. They use their tentacles to both catch and sting their prey. Some jellyfish stings contain poison. Due to the fact that many species of jellyfish are transparent, they are often hard for their enemies to spot. Jellyfish are drifters and move very slowly through the water sometimes using their tentacles to propel themselves along.
Jellyfish can vary in size from the length of your palm, to the being taller than a tall adult. They feed mainly on fish, eggs and invertebrates. Jellyfish are not a threatened species because they do not have many predators - that is not many animals hunt them for food. Moreover, jellyfish are good at adapting to new conditions so there is little danger of their becoming extinct in the near future.