What are the signs that distinguish flatworms from roundworms?

Worms are very widespread. Flat and round worms differ in both internal and external structure.
Roundworms have a cylindrical body shape, while flatworms have a flattened body shape. In round ones, the body is filled with liquid, and in flat ones, a loose substance. The digestive system in roundworms is a tube with an oral and excretory opening, and in flatworms it may even be absent. The nervous system of the round is a semblance of a brain with nerve branches, in flat ones, a set of nerve cells with branches of fibers. Roundworms are usually hermaphrodites, while flatworms are unisexual animals.
Also, the organs of vision may be present in flatworms.

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