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Platyhelminthes (e.g. flatworm) body form

Flatworms like the liver fluke are bilaterally symmetrical and flattened dorso-ventrally. This means they are flat back (top) to front (bottom). Their bilateral symmetry means they are identical when split into two, lengthways in this case (unlike Cnidaria which are radially symmetrical). 




They have a single opening (mouth) to the gut. Its flat body tissues support its body structure, with no specialised skeletal system. Many flatworm species are parasitic. They do not have an internal body cavity, circulation and respiratory systems, but do have a brain (in the sense of a more concentrated neuronal network in the front part of their body i.e. the head).




The flatworm lives in water or wet environments such as leaf litter, and has its flattened body in order to maximise diffusion across its body. The minimised diffusion pathway ensures it is quick enough to enable good gas exchange.

Having no anus, they regurgitate food as part of digestion, and hence cannot undergo a continuous process of digesting food.

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