Jellyfish are ubiquitous in the Earth’s oceans. They can thrive in warm water and cold, along coastlines or out in the deep. Their bodies are about 95 percent water. Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.