Jellyfish are typically free-swimming animals consisting of a gelatinous, inverted-umbrella body form (the bell) with trailing tentacles. Having roamed the sea for the last 500 (and maybe 700!) million years, they are the oldest known multi-cellular animal. Since jellyfish are not true fish, many experts prefer to use the name “jellies” to avoid cultivating misconceptions. The body of a jellyfish is between 95% and 98% water and most do not have specialized digestive, osmoregulatory, central nervous, respiratory, or circulatory systems. They can range in size from about 1 millimeter to a bell height and diameter of over 2 meters (6.6 feet). The lion’s mane jellyfish (Cyanea capillata) has fine, threadlike tentacles that may extend over 36.5 meters (120 feet!).