Pond Water Critters
that you can see with a microscope:
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 is 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 are identified regularly.

Find below links to images and descriptions of some common fresh water critters that you might encounter in your investigations with a microscope.  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.  (Note:  All images are copyrighted and cannot be used without permission.) 

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Phylum Ciliophora:  These critters are called Ciliates and have hundreds of tiny cilia which beat in unison to propel the protists through the water.  Shown at left is a school classic, the Paramecium. 

 Often cilia are fused together in rows or tufts (called cirri) and are used for special functions such as food gathering.  In addition to locomotion, the Paramecium uses cilia to sweep food down into it's central channel or gullet.  Other ciliates include the Stentor, Blepharisma, Bursaria, and Vorticella.  Click on the image to see more.

Phylum Mastigophora:  These protists move with a whip like extension.called a flagella.  The flagella is a long fibril that is spirally wound and beats or rotates in the water to move the protozoan about.  Included in this group is the Peranema (shown at left), the Euglena and the Volvox.  Click on the image to see more.

Phylum Sarcodina:  The amoebas.  They are a blob of protoplasm formed in a single cell.  By flowing their protoplasm forward into a "foot" then bringing the rest of their body into the foot, they can slither along.  Some Sarcodina have firm axial rods instead of pseudopods.  They move by motion in these rods.  Another classic high school protozoan is the Amoeba Proteus, shown at the left.  Click on the image to see more.


Multicellular animals:  These critters don't belong to the Kingdom Protista but rather the Kingdom Anamalia.  Some, like the rotifers look like protists and even have cilia but they are made of many cells and have organs like other animals.  Shown at the left is a very common pond water critter called a Rotifer.  If you study pond water samples, you will see rotifers.  Click on the image to see more.

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