Digestion

Free-living flatworms have a gastrovascular cavity with one opening at the end of a muscular tube called a pharynx (sucks food into the cavity). The cavity then forms an intestine with many branches along the entire length of the worm. Enzymes help break down the food into small particles, which are taken inside the cells of the intestinal wall, where digestion is completed. Because the intestine branches into nearly all parts of the body completed digested food can diffuse to other body tissues.

Some parasitic flatworms have a pharynx that pumps food into a pair of dead-end intestinal sacs where the food is digested. Their digestion is simpler than free-living worms, such as tapeworms, who do not have digestive tracts at all, but hooks/suckers with which they latch onto the intestinal wall of the host. They then absorb the food that passes by (already broken down by the host).

Roundworms however, have tube-shaped digestive tracts with openings at both ends, a very effective system. The anus is the opening in which any materials in the food that cannot be digested leave through.