ParameciumParamecium tetraureliaParamecium aureliaParamecium caudatumThe Paramecium is a group of unicellular ciliate protozoa formerly known as slipper animalcules from their slipper shape. They are commonly studied as a representative of the ciliate group. Paramecia range from about 50 to 350 μm in length, depending on species. Simple cilia cover the body which allow the cell to move with a synchronous motion. There is also a deep oral groove containing inconspicuous compound oral cilia (as found in other peniculids) that is used to draw food inside. They generally feed upon bacteria and other small cells. Osmoregulation is carried out by a pair of contractile vacuoles, which actively expel water absorbed by osmosis from their surroundings.Paramecia are widespread in freshwater environments, and are especially common in scums. Paramecia are attracted by acidic conditions. Certain single-celled eukaryotes, such as Paramecium, are examples for exceptions to the universality of the genetic code (translation systems where a few codons differ from the standard ones).credit : http://en.wikipedia.org/wiki/Main_Page