PROTOZOA Introduction

PROTOZOA Introduction
Traditionally the animal kingdom has been divided into two subkingdoms; Protozoa* and Metazoa* .
Protozoa are the most abundant animals in the world in terms of numbers and biomass. Their principal importance is as consumers of bacteria (PROKARYOTES ). Bacteria play a vital role in maintaining the earth as a suitable place for inhabitation by other forms of life and protozoa play a vital role in controlling their numbers and biomass. Protozoa are also important as parasites and symbionts* of multicellular animals.
Protozoa are defined as single-celled eukaryotic* organsims, that feed heterotrophically* and exhibit diverse motility mechanisms. However, it is impossible to draw a line between unicellular animals (consumers), plants (producers) and fungi (decomposers) and it is customary to speak of the Protista* as a separate kingdom of unicellular eukaryotes that embraces both heterotrophic protozoa and autotrophic algae.
Protozoan classification
Four major groups of protozoa are recognised and often given the status of phylum* . Note, however, that in the animal kingdom proper (Metazoa* ), phyla are distinguished on their different body plans and that no comparable body plans are found in Protozoa.
The groups are:
• flagellates (or Mastigophora)
• amoebae (or Sarcodina)
• sporozoans (or Sporozoa, Apicomplexa) and
• ciliates (or Ciliophora).The above classification represents a convenient filing system. We now know from molecular data (especially RIBOSOMAL RNA gene sequencing), that the different groups of flagellates and amoebae are not closely related and that there may be much greater genetic distance between two groups of flagellates than between flowering plants and vertebrates.
The above classification is not therefore phylogenetic* (i.e. reflecting the course of evolution). It is at present premature to try to construct a phylogenetic classification of protists, and for purposes of identification the above traditional classification is a starting point.

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