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Jellyfish are strange creatures, and they often send people in the other direction. This is because they are gooey, mushy, and if you step on them the wrong way, painful. Jellyfish contain the power to sting someone, but other than this elementary defense mechanism, they are harmless, and in some respects beautiful, creatures.
Jellyfish belong to the phylum Cnidaria, and they are invertebrates, or animals with no backbone. They contain a very simple nervous system. Their body is literally one big “bundle of nerves!” Their body contains a system of simple neurons that are capable of detecting food, light, warmth and vibration. Smell and taste are aided by chemoreceptors, which allow the jelly to detect odor and food. Light receptors allow the jelly to distinguish light and dark, but no shapes or external dimension. This system can be seen under their skin, which is translucent. They contain a thin outer layer of clear skin, and a gastrodermis, or an inner layer lining the stomach and inside cavity. The middle of the jellyfish is filled with the “jelly,” or mesoglea. Their mouth is typically underneath them as they move, and they contain a series of tentacles that help draw food inside them. Food, for the jellyfish, consists of plankton, comb jellyfish (the smallest variety) and other members of their own species. The inside cavity is a stomach, digestive cavity, intestine and gullet all in one. They contain one opening for both taking in food and letting out waste.
While they are fragile-less than 7% of a jellyfish is solid matter-jellyfish can live in almost any water. Extremely salt water is the only climate that they avoid. They can live at almost any depth, and some can reach up to over seven feet wide. The Arctic lion’s mane contains tentacles over 100 feet long! Several species contain a stinger, which can cause anything from light pain to burning for several days. This stinger is a stinging cell area made of nematocysts, sensory hair that are capable of firing a warning to animals and people. The Australian box jelly and the Portuguese man-of-war contain the most powerful stingers, and divers are advised not to provoke these creatures, because it may result in great injury or death.
While jellyfish have tentacles under their stomach, these usually limit them to moving either up or down. They can fill their stomach with water and contract quickly, propelling themselves in a straight line. They also contain special muscles on either side of their pulpy body that contract and pulsate according to the stimuli that their nerve endings receive. Other than these movements, they are generally at the mercy of people, winds, tides and waves.
Jellies mate in an interesting manner. The female will produce eggs around her mouth and underside, and the male fill fire sperm in her direction. The female gather the sperm with her tentacles and, in essence, uses them to fertilize herself. Her eggs then attach to her tentacles, and stay for a while until they are released into the water. They then attach to rocks, and sit for months, even years, in some cases producing replicas of themselves. They then split into several jellyfish, and swim away.
Jellyfish are being examined for potential cures for human diseases. They are also of great benefit to marine life at times, because of their living habits. Certain countries even regard the jellyfish as a delicacy, and serve it as food!
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