AMOEBA

These unicellular protists are able to change their shape constantly.  Each species has its own distinct shapes.  Amoebas move by forming false feet, called pseudopods, which they use to flow over a surface.  These psuedopods are also used to engulf their prey to capture it.

BACTERIA

Most bacteria are so small that they can only be seen as little dots under a light microscope.  They are the most ancient life forms, and the most prominent creatures in the early stages of life's history, about 4 billion years ago.

CILIATES

These unicellular protists can be recognized by their hairlike 'cilia', which they use for locomotion and feeding.  The cilia act like paddles.  They use food vacuoles to transport food through the cell.  Ciliates range in size from not much larger than the smallest bacteria, to a size of two millimeters, which is large enough to be seen with the naked eye.

CRUSTACEANS

Although crustaceans are usually thought of as crabs and lobsters, they also contain many microscopic relatives.  Crustaceans have segmented limbs and a hard external skeleton made of chitin.  When you look at a drop of pond water under a microscope you will likely see water fleas, ostracods, and copepods, all of which are crustaceans.  Water fleas use large antennae for locomotion and can be seen with the naked eye.  Ostracods' shells fossilize well because they are so strong.  They can shut the two halves of their shells and retreat into them.  Ostracod fossils are very important in determining the age of prehistoric earth layers.  Copepods are perhaps the most numerous animals on earth.  While they may not be as common in fresh water, they are found in the ocean in vast numbers.

DESMIDS

Freshwater single celled green algae.  Their spectacular symmetrical shapes can only be view through a microscope.  They can be recognized because of their symmetry.  Many secrete mucilage through pores in their cell walls, and they reproduce using fission.

DIATOMS

Although they are able to photosynthesize, these delicate unicellular organisms have a yellow-brown chloroplast, instead of the usual green.  Diatoms can be divided into the pen-shaped pennates, and the cylinder shaped centric.  Most fresh water diatoms are pennate.

FLAGELLATED PROTOZOA

The word 'protozoa' refers to the more animal-like single celled organisms, while the word 'algae' refers to those that are more plant-like.  Flagella refers to the whip-like parts of an organism used for locomotion, feeding, and other purposes.  Most flagellated protists have at least two flagella.

GREEN ALGAE

Algae is groups of microorganisms, often unrelated, that are able to perform photosynthesis.  Although green is usually the color associated with photosynthesis, different types of algae can have different colors of chloroplasts, so algae can be brown, red, blue green, and many different shades of green.  Some species' chloroplast changes color when growing conditions are unfavorable.  While most species are flagellated and motile, some are only flagellated at a certain stage in their life cycle, and immobile the rest of the time.  

AQUATIC INSECT LARVAE

Since most insects are partially, if not completely, aquatic, every pond you find will contain insect larvae.  Although they are not microscopic, they have many interesting features that can only be examined under a microscope.  Insect larvae are transparent, so they can be studied quite easily with a low powered microscope.  If you look carefully, you will observe the blood flowing through the body.

ROTIFERS

Although most people have never heard of them, rotifers are actually small, multi-celled animals.  Although their cells number less than 1,000, rotifers are specially equipped for their lifestyle.  They have a crown of cilia located at the front of their bodies for locomotion and waving food into their mouths.  Some have a foot that secretes a sticky substance enabling them to attach to any surface.  

WORMS

A worm is an animal that has a slender elongated body shape that works well for a certain life style.  Worms can be distinguished by their mode of travel.  Oligochaetes wriggle using setae, flatworms use tiny cilia to slowly glide, and nematodes move in frantic s-shaped curves.

SUN ANIMALCULES

Sun animalcules have axopodia, which are long, stiff projections of cytoplasm.  They have limited ability for movement, but are skilled at capturing prey.  They eat small protists, which stick to the axopods, and are then covered by the cytoplasmic flow and transported towards the cell.  Two are sometimes found feeding on the same prey.