In biology, a medusa–plural: medusae–is a form of cnidarian in which the body is shaped like an umbrella and the rest of the body are tentacles that can be of various lengths and forms. Cnidarians are a very old group of aquatic animals that have been around in the oceans for over 600 million years and include thousands of species, including corals. Jellyfish are an essential part of the biosphere and are resilient to dramatic environmental changes, hence their longevity as a group. I love their elegance. Some of them are very poisonous, The Cubomedusae, for example, can kill a person in agonizing pain just by touching them. They kill more people than sharks every year for example. So, both beautiful and dangerous… my kind of organism! The amazing part is that they are between 95% to 98% composed of water.