Intro
Platyhelminthes is essentially Flatworm. They are very simple, unsegmented, and soft-bodied. There are no circulatory or respiratory organs which causes the flattened shape in order to let oxygen and nutrients to diffuse through. They are divided in to parasitic and non-parasitic groups. You have the Turbellaria which are non-parasitic and then three different parasitic groups which are Cestoda, Trematoda, and Monogenea. Flat worms are mostly predators and live in water or a shaded, humid, terrestrial environment. Some flatworms are especially harmful to humans and livestock.
Nervous System
A flatworm has a very simple nervous system with two chords running down either side. It has two brains called ganglia, which are simple bundles of nerves. It also has two light spots to help it sense light.
Cestoda
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These are more commonly known as tape worms. They often live in animals all their life. When they are young they live in bodies of various animals but as adults they live in the digestive track of vertebrates. It is often contracted by consuming unprepared meat.
Monogenea
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A monogenea is a small parasitic flatworm found on skin or gills of fish. They lack circulatory, respiratory, and skeletal systems. Also they have no oral suckers. They attach to other organisms by a series of hooks, clamps, and other specialized structures. They also have no body cavity. All they have is a simple digestive system.
Turbellaria
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This is a non parasitic sub group with about four thousand five hundred species. They have a lack of a respiratory and circulatory system so they have to rely on difusion. Most are predators and live in water or moist land environments. These also reproduce sexually. The way they move depends on their size. If they are small then they use cilia for motion but if they are large they use muscular motions to move.