Examples of Protozoa with Detailed Characters & Pictures

Protozoans are the microorganisms present on land and water.

These are the animals that have a single cell yet live independently.  They are

  1. Ameoba
  2. Euglena
  3. Paramecium
  4. Entamoeba
  5. Trichomonas
  6. Leishmania
  7. Plasmodium
  8. Trypanosoma
  9. Giardia
  10. Blanditidum
  11. Vorticella
  12. Stentors

These protozoans are of different shapes and sizes and have varying habitats. Many of them are free-living, while others live as parasites.

Because of the single-celled feature, they resemble bacteria. But unlike bacteria, they are eukaryotes and do not possess a cell wall.

They perform all their physiology, including reproduction, movement, and food collection, with that single cell.

Protozoa Examples Include

1. Amoeba

Amoeba a protozoa
Amoeba without any specific shape and external organelles for movement.
  • Amoeba is a protozoan that has no specific shape. It is the most common protozoan found in freshwater.
  • They live independently and move in search of food. Most freshwater protozoa are microscopic.
  • They cannot be viewed with the naked eye and need the help of a microscope. However, the marine amoebas are relatively large and are visible to the naked eye.
  • The structure is so simple, with no specialized appendages or sexual parts.
  • They move by pseudopodia, the extensions of the cell membrane and cytoplasm.
  • The cell has a contractile vacuole, which helps to remove excess water from the cell.
  • Since the cell cytoplasm is more hypertonic than the surrounding fresh water, the water tends to accumulate inside the cell.
  • The vacuole expels this accumulating water.
  • They do not have a mouth but engulf solid particles by phagocytosis from any point of the cytoplasmic membrane.
  • They also drink dissolved forms of liquid nutrients by pinocytosis. Their food includes live microbes like bacteria and dead organic matter.
  • They reproduce by binary fission asexually.

However, recent studies showed them even to have sexual means of reproduction.

Some types of amoeba also cause severe diseases in humans.

2. Euglena

Euglena an Examples of Protozoa living in fresh water
Euglena with both plant and animal-like features
  • This is an eye-shaped freshwater protozoan.
  • They impart a green color to the water ponds when grown extensively.
  • Unlike amoeba, they have well-developed cell organelles like eyespot (Stigma), flagella, etc.
  • Unlike amoeba, they can act as autotrophs as they make their own food.
  • The eyespot contains chlorophyll-like pigment, by which they perform photosynthesis.
  • They can also live as heterotrophs and eat external substances. 

Hence, they have both plant and animal characters.

3. Paramecium

This is a slipper-shaped protozoan.

It has cilia all over its body surface, and these cilia help in its locomotion.

Paramecium a slipper shaped protozoan
Slipper-shaped paramecium with cilia
  • They are found in freshwater and are more evolved than the amoeba.
  • They have a mouth, cilia, and vacuoles for the expulsion of waste out of the cell.
  • They undergo sexual reproduction by the method of conjugation.

Disease-causing protozoa

4. Entamoeba histolytica

  • This is an amoeba that infects the large intestine and other tissues.
  • It spreads through contaminated water and food.
  • It is anaerobic and resides in a low-oxygen atmosphere.
Entameoba in intestine by CDC
Entamoeba in the intestine (cdc.gov)
  • The infection causes severe pain in the abdomen and loose stools with mucus.
  • Unlike typical amoeba, it has a single pseudopod.
  • It is a mono-genetic parasite, i.e., it completes its life cycle in man (single host).
  • In the intestine, it resides in the mucous and sub-mucus layers.
  • It secretes an enzyme, namely “Histolysin,” which dissolves the mucus tissue.

5. Trichomonas vaginalis

  • It is a protozoan that causes vaginal infection in humans.
  • The protozoa are flagellate and also anaerobic.
  • It is a type of sexually transmitted disease.
  • The symptoms of infection do not appear in women but appear in men.

6. Leishmania

  • Leishmania is of two kinds: Leishmania donovani and Leishmania tropica.
  • It causes kala-azar (dum dum fever) and visceral leishmaniasis.
  • In comparison, L.tropica affects the endothelial cells of skin capillaries.
  • It is spread by the bite of an infected Sand fly.

7. Plasmodium

  • Commonly known as a malarial protozoan parasite.
  • It is spread from human to human by the bite of a female Anopheles mosquito.
  • This protozoan is of 4 types: plasmodium vivox, P. falciparum, P. malaria, and P. ovale.
  • Of them, plasmodium falciparum is considered to be deadly as it is responsible for 50% of malarial cases.
Plasmodium human parasitic Protozoa
Image By Jfbranch14/commons.wikimedia.org
  • The protozoa in humans reside in the red blood cells.
  • It eats up hemoglobin and converts it into the poisonous substance hemozoin.
  • When the RBC breaks down, the hemozoin is released, causing chills, headaches, and fever.
  • They have a cycle of 24 hours, so they break down the infected RBC and attack news every 24 hours.
  • So, the infected person experiences feverish symptoms in intervals of 24 hours.

8. Trypanosoma gambiense

  • This is a protozoan that causes African sleeping sickness.
  • The bite of a tsetse fly spreads this protozoan from one person to another.
Trypanasoma gambiens (Parasitic Protozoa)
Diagram of protozoa Trypanosoma by Food and Agriculture Organization of the United States.
  • The parasite is oval-shaped and has flagella. It is a digenetic parasite.
  • The first host is a man or animal, and the second host is an insect called a tsetse fly.

9. Giardia intesinalis

  • It is an intestinal parasite residing in the small intestine.
  • It causes abdominal pain and diarrhea.
  • It is spread by contaminated water.
  • As seen in the picture above, it has two nuclei and 4 flagella.
  • They do not possess mitochondria and instead, a modified endomembrane complex helps in energy generation.

10. Balantidium coli

  • It is a ciliated parasitic protozoan living in the large intestine.
  • As seen in the picture below, it has two nuclei.
  • One large and one small nucleus lie close to each other.
  • A mouth called cytosome or peristome is present.
Balantidium another Example of ciliated Protozoa
  • The transmission to man occurs from pigs. It causes ulcers and chronic dysentery.


  • These are bell-shaped ciliates living in mud and freshwater.
  • They eat bacteria and sometimes survive on the surfaces of mosquitoes, prawns, etc.
vorticella a protozoan
  • While moving, they make a vortex in the water, hence the name.


  • These are trumpet-shaped protozoa.
  • They dwell in freshwater, and some are found in marine waters.
  • They have a symbiotic relationship with a few algae.
  • Protozoan’s physical structure is a simple cell.
  • They have a distinct nucleus and other essential organelles, and they also possess the ability to move.
  • Most of them are harmless and live in freshwater or seawater.
  • Some of them make their food by photosynthesis, while others are dependent on other organic debris for food.
  • To the extreme, a few of them are also parasites.

Further, they are grouped into the animal kingdom due to marked similarity to animals.

Read more on single-celled organisms.

Frequently Asked Questions and Answers.

Are protozoa photosynthetic?

Few protozoans, like Euglena, are photosynthetic. But not all of them.


Leave a comment

Leave a Comment