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Coelenterata
Coelenterata is an obsolete term encompassing two animal phyla, the Ctenophora (comb jellies) and the Cnidaria (coral animals, true jellies, sea anemones, sea pens, and their allies). The name comes from the Greek "''koilos''" ("hollow bellied"), referring to the hollow body cavity common to these two phyla. They have very simple tissue organization, with only two layers of cells, external and internal and radial symmetry. Some of the examples are corals, sea anemone which are colonial and hydra, jelly fish which are solitary.
== Characteristics ==
All coelenterates are aquatic, mostly marine. The bodyform is radially symmetrical. The body has a single opening hypostome surrounded by sensory tentacles equipped with either nematocysts or collobasts to capture mostly planktonic prey. These tentacles surround a spacious cavity called the gastrovascular cavity or coelenteron. Digestion is both intracellular and extracellular. Respiration and excretion are accomplished by simple diffusion. A network of nerves is spread throughout the body. Many forms exhibit polymorphism, wherein different types of individuals are present in a colony for different functions. These individuals are called Zooids. These animals generally reproduce asexually by budding, though sexual reproduction does occur in some groups.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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