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Physiology Jellyfish have no brain, blood, or heart, but they still manage to survive. Jellyfish have a bell-like body with tentacles flowing underneath. They may have one or more mouths in the center of their body, between the tentacles. Around the mouth(s) there are tiny, frilly arms. Jellyfish range in size from the thimble jellyfish, which are only a few centimeters, to the Lion's Mane jellyfish, who's tentacles can reach a length of over 100 feet. Most jellyfish are transparent and have a white to light blue tint to them. The jellyfish moves using a jet propulsion method. Jellyfish have special muscles on the underside of their body that contract and shoot out water, moving the jellyfish. Jellyfish also have special light sensory organs along the rim of the body. These organs can detect light and dark, but can't pinpoint exact objects. Dispite not having a brain, jellyfish can still taste and smell. Diet Jellyfish eat tiny planktonic creatures such as small fish, larvae, and other jellyfish. Jellyfish have sensors in their tentacles that can detect movement around them. When movement is detected, stingers shoot out and into the cause of the movement. If the object is prey, the jellyfish will eat it. Then the jellyfish will quickly flee. Habitat Jellyfish are found throughout the world, in every ocean. Species live in both deep and shallow coastal waters. It's the species of jellyfish that live in the coastal regions that come in contact with humans the most. Predators Sea turtles and certain kinds of bony fish, like the sunfish, do eat jellyfish on a regular bases. Even humans eat jellyfish but not enough to make them endangered. Most people fear jellyfish for their painful stings. Most of the time, jellyfish stings only cause a rash; but in some people, they have been known to cause death. Reproduction In most species of jellyfish, the reproduction goes through four stages. First the female lays eggs and caries them around her mouth. The eggs grow into small round, flat, disc shape larvae. The larvae is released and travels through the water until it reaches a hard surface, such as a rock or coral. Once it reaches the hard surface it transforms into a polyp, much like a sea anemone. A polyp is a animal with a mouth at on end and a disc-like foot at the other. It may take a jellyfish several years to complete this stage of turning into a polyp. During this time it may produce exact copies of itself by breaking off parts of itself which grow into complete polyps. When the polyp stage is complete, the polyp divides into different sections an it resembles a stack of pancakes. One by one a layer swims off and becomes a tiny miniature of an adult. Once a jellyfish become an adult it only lives for 2 to 6 months.
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