Flatworms have bilateral symmetry and they are the first animal group with a head. They also have organs and systems including testes, ovaries, and kidney-like structures. Some examples of flatworms are planaria, fludeworms, and tapeworms. Roundworms have a body cavity filled with fluid that houses the organs. It serves as a circulatory system and also makes the worm rigid, like a hydrostatic skeleton.
Roundworms are parasitic to both animals and plants.
Some examples are trichinella, found in pork, pinworms, hookworms, and brainworms. In lab, we collected deer feces, enticed the brainworm larvae out of the feces with warm water, and collected the sample to study under the microscope. The larvae of the brainworm is found in the deer feces. Snails eat the larvae. Later, deer eat the snails and come in contact with the brainworm as larvae again.