The single-celled eukaryotic organisms can live inside the tissues and cells of humans and other organisms, to cause diseases in them are referred to as parasitic protozoans.
Parasitic protozoans are found in marine and freshwater.
Example of parasitic protozoa: Plasmodium falciparum that causes malaria.
It is an example of parasitic protozoa that causes malaria in human beings.
Plasmodium doesn't have any specialized structure for locomotion.
It spreads malaria in humans from the bites of infected Anopheles mosquitoes.