They are very small, predatory animals mostly live in salt water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. Some of the species live in freshwater.
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These are referred to as the "true" jellyfish. Scyphozoans have no hard parts, such as no head, no skeleton, and no specialized organs for respiration or excretion. Marine jellyfish can consist of as much as 98% water causing them to rarely be found as fossils.
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The cubazoas are the box jellies and unlike the true jellies they are viewed as square from above. With there very unique anatomy box jellies can move at up to speeds of 6 meters per minute(thats very fast for a jellyfish).
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Anthozoans are probably the most famous cnidarians, they include the corals that build great reefs in tropical waters, as well as sea anemones, sea fans, and sea pens. These animals have had fossils found from close to 560 million years ago.
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