Classification is needed because there are large number of living organisms on earth. To study the diversity among such a large group separately at an individual level is almost impossible. Hence, to make the studies more systematic, it is important to classify various kinds of organisms in an ordered manner. The similarities and the differences help us understand the inter-relationships among different groups of animals and understand evolutionary processes and the geographical distribution of plants and animals. Thus, classification also forms a base for other biological sciences, such as evolutionary biology and biogeography.