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| Phylum Platyhelminthes |
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 Bilaterally symmetrical, triploblastic true multi-cellular animals with organ grade of organisation. |
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 Free living (aquatic or terrestrial) or parasitic (ecto- or endoparasites). |
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 Body is dorso-ventrally compressed, leaflike. |
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 A body cavity is absent. Space between body wall and alimentary canal is filled with mesenchyme (connective tissue). |
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 Digestive system is incomplete. Anus is absent. |
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 Respiration by simple diffusion. |
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 Excretion with the help of specialised cells called flame cells or solenocytes. |
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 Nervous system is ladder-like consisting of a brain and a pair of longitudinal nerves connected by many transverse nerves. |
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 Reproduction is usually by sexual methods. Majority of the forms are bisexual (hermaphrodites). Development is direct or indirect. |
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 Body is triploblastic. |
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 They have blind sac body plan. |
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| fig. 10.9 - Examples of Platyhelminthes |
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| The phylum is divided into three classes |
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| fig. 10.10 - Planarian Anatomy |
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