Paramecium is one of the best-known protists, often taught in school biology courses. Paramecium is the most complex and specialized of the protists. It is a ciliate genus. Ciliates are a group of protists which move by waves of tiny hairlike projections from their cuticle. They live in freshwater ponds, and eat bacteria, and other protists such as algae. Paramecium species usually have bacterial symbionts, and some species have green algal symbionts. Symbiotic bacteria are bacteria living in biological interaction with another organism or each other.
Paramecium are slipper-shaped and nearly see through. The body of a paramecium is not symmetrical. It has a well-defined ventral or oral surface and has a circular body surface. Its whole body is covered with a flexible, thin and firm membrane called pellicles. These pellicles are elastic in nature which supports the cell membrane. They are covered in a protective skin that functions and protects them from the elements. On the edges of the skin are the cilia, or tiny hair-like structures.
Paramecium usually feeds on micro organisms such as bacteria, algae, and yeast. In order for the paramecium to gather its food, it uses its cilia to sweep food, as well as water, into oral grooves and into the organism's mouth. The food then passes through the mouth and into the cells.