From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants. Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exit in under water reef formations in tropical oceans.
Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15, 000 new organisms are discovered every year. It is not possible to find out an organism of known characters from the vast number of organisms. A clearer understanding of this huge variety of organisms can be studies by dividing these into smaller groups of sub- groups (categories) and each group or sub-group comprising of organisms with more or less similar characters. This method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification. The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or