Protozoans: Animals or Protists?

Protozoans are single celled eukaryotes found worldwide with rich biodiversity. The protozoan species live in different habitats as free living or parasite having different shapes and adapted for various physiological activities. These are microscopic unicellular eukaryotes that have a relatively complex internal structure and carry out complex metabolic activities within a cell by highly specialized subcellular organelles like pseudopodia, flagella and cilia. Initially protozoans were kept in phylum Protozoa under kingdom Animalia as per classification of Linnaeus but later placed under kingdom Protista from three to six kingdom systems. In present article, author attempted to discuss the position of protozoa from two to six kingdom system of biological classification and finally concluded that protozoans are now protists, and not the animals