Protozoa or Protozoa: What They Are, Characteristics and Classification

Protozoan or protozoan is a eukaryotic unicellular organism with mitochondria, ability to phagocytose, and no cell wall. Fungi, plants, and animals are thought to have evolved from protozoan ancestors.

For a long time, protozoa were classified together with algae in the kingdom Protista. In the most recent classification of living things, the protozoa or protozoa are included in their own kingdom, the kingdom Protozoa.

Many parasites that cause disease in humans are protozoa, such as Trypanosoma cruziwhich causes Chagas disease and entamoeba histolitica, which causes amoebiasis. However, not all protozoa are harmful, and they prefer to live freely in puddles, lakes, rivers and seas.

Other examples of the importance of protozoa are found in the protozoa that form the benthos (aquatic ecosystem bottom), the edaphon (community that inhabits the soil). In general, protozoa, despite not being complex organisms, are essential in promoting environmental and ecological balance.

examples of protozoa or protozoa vorticella trypanosome amoebae and paramecium

Examples of protozoa. Up: vorticella (left), amoebas (right). Down: Stichotricha second (left), trypanosome (right).

Characteristics of protozoa

  • They are unicellular: hehe protozoa are characterized by being cells that live independently without forming differentiated tissues.
  • are mobile: they can move through creeping or by appendages that they have as cilia or flagella.
  • have a nucleus: where the genetic information of the organism is stored.
  • They live in aqueous media: Generally, protoszoans inhabit liquid or aquatic environments of fresh or salt water.
  • They are phagotrophic heterotrophs.: they feed by swallowing the material that they capture abroad, that is, they do not have a digestive system like animals, nor are they capable of photosynthesis like plants.
  • They do not have a cell wall: unlike fungi and plants, protozoa do not possess a protective outer covering of the plasma membrane.
  • Get energy through cellular respiration: protozoa are capable of transforming what they consume into adenosine triphosphate ATP, using oxygen and releasing carbon dioxide.
  • have mitochondria: These are the first organisms in the evolution of life to have mitochondria.
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Classification of protozoa

The kingdom of protozoa presents the following subdivisions or phyla:

Percolozoa Edge

They are protozoa that do not have a Gogi apparatus, such as Percolomonas and Naegleria fowleria parasite that is also known as “the brain-eating amoeba”.

Phylum Euglenozoa

This group includes trypanosomes, such as the Trypanosoma cruzi (producer of Chagas disease) and the Trypanosoma brucei (producer of African trypanosomiasis).

Metamonada Edge

Protozoan with a flagellum and no mitochondria, like the trichomonas vaginalis and the Giardia lamblia.

Phylum Amoebozoa

They are amoeboid protozoa, they form pseudopodia or false feet with the plasmatic membrane. Examples are the Entamoeba histolytica, that produces amoebiasis, and Endolimax nana.

Apicomplexa Edge

Protozoa that parasitize animal cells, such as toxoplasma gondii (producer of toxoplasmosis) and the Plasmodium sp.. (producer of malaria or paludism).

Ciliophora phylum

They are ciliated protozoa, they move through cilia or short filaments on their surface. Some examples of ciliates are the paramecia.

See also Kingdoms of nature


Cavalier-Smith, T. (1993) Kingdom Protozoa and its 18 Phyla. Microbiological Reviews. 57:953-994

Ruggiero MA, Gordon DP, Orrell TM, Bailly N, Bourgoin T, Brusca RC, et al. (2015) A Higher Level Classification of All Living Organisms. PLOS ONE 10(4): e0119248. doi:10.1371/journal. puts.0119248