For over 500 million years, the jellyfish has survived in our oceans. Today, global warming and pollution may be contributing to a population explosion, as billions of these sometimes venomous creatures increasingly swarm around our beaches and shorelines. And though they have no bones, blood or brain, some jellyfish are armed with a deadly arsenal unlike any other on the planet. National Geographic dissects the fascinating physiology of this living fossil, from it's 24 clustered eyes down to the tips of it's stinging tentacles, and examines how mans impact on the environment may be creating a growing invasion.