Paramecium is one of the simplest unicellular organisms, which is found in almost all water body related environmental conditions. Classification Provided below is the scientific classification of paramecium. This protozoan is a member of the group of living beings, known as animal kingdom. It belongs to the class Ciliatea of the phylum Protista. Paramecium is its genus name, and there are several species of this protist, namely aurelia, bursaria, caudatum, trichium, etc. Description Paramecia are oval, slipper shaped, and unicellular organisms, and are commonly found in freshwater environment. Their body is slender and roughly cylindrical, with a thick and pointed posterior end, and a blunt or rounded anterior end. Depending on the type of species, their length ranges from 50 to 300 µm. The whole body is covered by a thin protective membrane, known as pellicle. This stiff outer covering imparts the particular slipper shape to the microorganism. The pellicle is covered by tiny and thin hair-like structures called cilia. These structures are the characteristic features of all members belonging to the class Ciliata. The cilia play a key role in paramecium movement. Underneath the cell membrane, there exist a thin and clear layer of ectoplasm, which encloses the cytoplasm. Other structures like granules, vacuoles, and spindle shaped trichocysts are present in this layer. Paramecium has two distinct nuclei, which are responsible for different functions. The protist also possesses a definite digestive tract and a peristomial oral groove, which is covered with cilia all around it. It helps in the case of holozoic type of nutrition. Paramecium is capable of both sexual or asexual reproduction types. Locomotion in Paramecium The whole body of this protozoan is covered with fine protoplasmic cilia, which are arranged in definite longitudinal rows; these structures serve as its locomotive organs. The cilia beat in unison against the water in a particular direction, just like oars in a boat. For example, if the organism has to move forward, the cilia beat at a particular angle in the backward direction. This helps them to move forward, spiraling through the water around an invisible axis, in pursuit of food. Paramecium generally thrusts itself forward, traveling in a straight line through the water. However, it is capable of changing its direction, when it comes in contact with a solid object or a predator. In such a case, the cilia immediately start beating in the opposite direction. This helps the paramecium to go backward, and turn in a direction away from the predator. The spiral movement or the spinning nature allows it to collect food, which is pushed by the cilia into the oral groove. They possess certain chemical sensors, which enable them to locate food sources.