In accordance with the Linnaeus method, scientists classify the animals, as they do the plants, on the basis of shared physical characteristics. They place them in a hierarchy of groupings, beginning with the kingdom animalia and proceeding through phyla, classes, orders, families, genera and species. Classification is arranging organisms into groups or sets on the basis of similarities and differences. In fact, to understand the living world classification gives a picture of all life forms at a glance and makes the study of a wide variety of organisms easy. It is also essential to understand the interrelationship among different groups of organisms. Animals are those organisms which are eukaryotic, multicellular and heterotrophic in their mode of nutrition. Except few, most animals are mobile and do not have cell wall. The more features that a group of animals share, the more specific that animal classification group is.