Since Cnidarians live in aquatic environments, they need to be able to survive in water. To do this, they must have special body structures. For instance, to be able to move in the water, jellyfish have a special type of skeleton called a Hydrodtatic Skeleton. This type of skeleton is a skeleton where muscles surround a water-filled body cavity and the muscles are supported by this cavity. This type of skeleton allows Cnidarians to move quickly and easily through the water. As well, Cnidarians do not have teeth to bite into prey. Since they need to feed, Cnidarians use their nematocytes to stun, kill, or paralyze their prey. They may even use their tentacles to drag their prey into the "mouth" alive. Because cnidarians are living in the open sea with many predators, they need a form of protection. So, not only do nematocysts help feed the cnidarian, they help protect them as well. When a predator, like humans, touches the cnidarian's nerve net, the trigger cells are activated. This, in turn, signals the firing of a nematocyst. The nematocyst then injects a toxin into the predator. This toxin, in some cases, can be fatal. In other cases, like humans, getting "stung" by a cnidarian just results in a burn. As we can see, Cnidarians are more than fit to survive in their aquatic environment.