What is Protozoa?
Protozoa, their very name meaning "first animals", are found on every continent as they are swept along by tides and currents of oceans and streams. They can even be blown along by winds as they have the ability to protect themselves from heat and drought in cysts- self-made houses of cemented-together grains of sand -until they find themselves someplace where conditions are right to resume their life functions. They can exist internally in other animals. Protozoan parasites are rather well distributed throughout the animal kingdom.
Protozoa are solitary cells or colonial, and nearly all microscopic.
They are not found in large masses like the algae. A few are large enough to be seen with a hand lens, and some even with the naked eye. These animals are classified chiefly according to their means of locomotion. The flagellate protozoa swim by means of a whip-like extension of the cell. The ameboid protozoa actually flow along in the water by extending pseudopods or "false feet."
The ciliated protozoa (often called infusoria) move about by rhythmic functioning of cilia, "hairs." The spore forms have no special mode of locomotion and are all parasites.
The flagellate protozoa have both plant and animal characteristics.
Some of the flagellates appear green to the viewer, due to the presence of chlorophyll which enables them to carry on photosynthesis like the algae previously discussed. Some scientists consider the bacteria and flagellate protozoa to belong to a group called Protista, thereby eliminating them from both the plant and animal kingdoms. You will discover that the flagellates are being treated as animals in line with those scientists who have so classified them.