Planaria
The Planaria is a type of non-parasitic flatworm. These creatures are well known for regenerating parts of their body that may ave been lost. For example, a Planaria that as been cut in half will create two new animals. It's very interesting because these creature are harmless in a way. The planaria has very simple organ systems. The digestive system consists of a mouth, pharynx, and a gastrovascular cavity. The mouth is located in the center of the underside of the body. Digestive enzymes are secreted from the mouth to begin external digestion. The pharynx connects the mouth to the gastrovascular cavity. This structure branches throughout the body allowing nutrients from food to reach all extremities. They basically eat living or dead small animals that they can catch with their mouth which is very muscular and basically helps the gastrovascular cavity to digest the food. Food passes from the mouth through the pharynx into the intestines where it is digested by the cells lining the intestines. Then its nutrients diffuse to the rest of the body.