Cnidarians are 95% water and semi transparent. They exhibit radial symmetry. Their body parts are arranged in a circular pattern around a central axis, like the spokes of a wheel. They are in a free-floating stage, called the medusa, where they are free swimming with tentacles on the bottom of their bodies as part of their nervous system. Their main body is a sealed bell with one hole which moves the jellyfish forward by contracting and forcing water out. They use their stinging cells, nematocysts, to capture prey and paralyze them. Many species of cnidarian have powerful stings. Symptoms can include an immediate, intense, burning pain with redness and swelling. You may also experience weakness, nausea, headaches, etc. Their sting is usually nonfatal to humans, unless they are allergic to the toxin. Cnidarians are important in the oceanic food chain and ecosystem, as they are carnivorous and prey on zooplankton, comb jellies, and other marine organisms. They are the prey of sea turtles, sunfish, and spadefish.
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