Protozoans and Small Animals

When you look at fresh water with a microscope you will likely see a variety of tiny living things. Sources of fresh water samples can include ponds, lakes, rivers, aquarium tanks or even an old rain puddle.

You might see bacteria which belongs to the Kingdom Monera. You likely will see tiny animals like rotifers which belong to the Kingdom Animalia and of course, there are the Protozoans and Algae which belong to the Kingdom Protista. The algae are single celled plant-like protists and the protozoans are single celled animal-like protists. Remember, the Protists are neither animals or plants but in a Kingdom of their own!

Protozoans are further classified according to how they move and there are four types. The phyla Mastigophora move with a long whip like extension called a flagella. The Ciliophora have hundreds of tiny little “hairs” which beat in unison like little oars to move them through the water. The Sarcodina includes the Amoebas and they move like a flowing blob of jelly using what is called a “pseudopod”, or false foot. The last type of protozoan are the Sporazoans. They are very small spore-like with no apparent means of locomotion. Some are harmful like those that cause malaria.

Scientists estimate that there are over 50,000 different species of protozoans. Even at that, there are many new protists yet to be found as new species that are identified regularly. Take a look at some info on Actinophrys Protists here.

Find below links to images and descriptions of some common fresh water critters that you might encounter in your investigations with a compound microscope (high power). Click on the small image to go to a page of that group. If you are trying to identify a particular protozoan, first determine how it moves then search the corresponding section below. When looking through the microscope at bacteria or protozoans, start at the lowest magnification to focus, then move up to 400x to view your samples. (Note: All images are copyrighted and cannot be used without permission.)

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