As a group the protozoa are most primitive and are inhabiting the earth for about a billion and half years. Fossil forms of radiolaria and foraminiferans, half a billion years old, have been recorded. Origin : Pre-Cambrian Taxonomic Retrospect : Leeuwenhock (1676) first gave preliminary accounts of some protozoan forms after the discovery of microscope. Goldfuss (1818) coined the term Protozoa but he included many non-protozoan forms under protozoa. Von Siebold (1845) recognised the unicellular nature of the protozoa and established the term Protozoa in its true sense. The zoologists like Doflein (1901), Colkins (1901, 33), Kudo (1931, 77), Hyman (1940), Honigberg (1964), Grell (1973), Corliss (1967, 84), Cavalier-Smith (2002) and Brusca and Brusca (2003) have classified the protozoa in different angles and have discussed on different aspects. Definition : Unicellular or acellular, eukaryotic and commonly motile heterotrophic organisms are