Protozoa are single-celled animals that come in many shapes and sizes.  The most common shapes are round, oval, bell-shaped and slipper-shaped.  Protozoa are clear.  They become the color of the materials inside them, including the food they just ate.

Scientific name: There are thousands of species of protozoa. Some groups found in vernal pools are: Vorticella, Heliozoa, and Amoeba.
Phylum: Protozoa
Habitat: Most aquatic habitats on earth
Size: Microscopic, 2 to 70 microns (0.002 to 0.07 mm)

Fun Facts:

Some species of protozoa use other vernal pool critters as taxis! With a microscope, you can see a species of Vorticella attached to the bodies of Seed Shrimp and Water Fleas. The Vorticella gets a free ride, and finds food along the way.

A different vernal pool species of Vorticella lives in groups. They let a certain species of green algae live inside their bodies. Some scientists believe that the Vorticella are “farming” the algae. This means that they use the food produced by the algae for themselves.

Heliozoa is a protozoan that looks like a soccer ball with spikes. The spikes are covered with a sticky substance that is poisonous to other protozoa. Any protozoan that touches Heliozoa is instantly paralyzed. Heliozoa sucks out the insides of its prey and eats it.

Life Cycle:

Most protozoa reproduce by cell division. The cell splits apart and forms two cells that are identical to the original cell. When food runs out or it becomes too dry and hot in a vernal pool, protozoa form a resting cyst with extra layers of walls around it. The walls protect the cyst until the pools are wet again. They hatch in just a few minutes once the rains return in winter.


Protozoa eat bacteria, detritus, algae and other protozoa. Protozoa are eaten by Water Fleas, Flatworms, Seed Shrimp, Clam Shrimp and many other vernal pool invertebrates.


Find out which vernal pool species eat critters that feed on protozoa?