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| Phylum Coelenterata |
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 Radially symmetrical, diploblastic multicellular animals with a tissue grade of organisation. |
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 Aquatic, freshwater or marine solitary or colonial forms which may be free swimming or sedentary. |
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 Body has a mouth at the oral end which leads into a spacious cavity called gastrovascular cavity or coelenteron. |
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 Presence of long, hollow structures called tentacles used for locomotion and food capturing. |
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 Presence of peculiar type of cells called cnidoblasts, nematocysts or stinging cells in the ectoderm, especially in the tentacles, used for offence and defence. |
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 Digestion is both intracellular and extracellular. |
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 Respiration and excretion by simple diffusion. |
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 Presence of a network of nerves spread all over the body. |
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 Many forms exhibit polymorphism, wherein different types of individuals are present in a colony for different functions. These individuals are called Zooids. |
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 Reproduction asexually (external budding) or sexually (formation of gametes). |
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| fig. 10.7 - Examples of Coelenterata |
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| The phylum is divided into three classes |
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| fig. 10.8 - Anatomy of Hydra |
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