Parasitic protozoa are classified mainly into four groups. They are:
(a) Rhizopoda (Plasmodroma):
The organisms of this group move by producing pseudopodia. They multiply by binary fission and form cysts, as in E. histolytica.
The organisms move by means of flagella, binary fission takes place by longitudinal division e.g., Trypanosoma, Leptomonad etc.
They move by amoeboid movement with change in form and position and they have no organ of locomotion. These organisms multiply by the process of schizogony within the vertebrate host and sexually by the method of sporogony (reduction division).
Fusion of gametes is followed by sporozoite formation in a sporocyst as in the invertebrate host e.g. Anopheles mosquito in human malaria caused by Plasmodium vivax, P. ovale, P. malaria, P. falciparum.
(d) Ciliophora (Ciliates):
The organisms move by cilia and multiply by transverse division of the body. They also produce cysts, e.g. only pathogenic species is Balantidium coli (Table A.1 and A.2).