• Protozoa or Cornelius protozoans (from Greek proton "first" and zoa "animals"; singular protozoon; (the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular   eukaryotes.
  •  All Protozoans are heterotrophs and live as predators or parasites.
  •  They are believed to be primitive relatives of animals.
  • They may be broken down into four primary categories, which are as follows:
    • Ciliated Protozoans:
      • They are mostly Aquatic animals.
      • They are actively moving organisms because of the presence of thousands of cilia.
      • They have a cavity (gullet) that opens to the outside of the cell surface.
      • The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet.  Example- Paramecium.

      • Amoeboid protozoans:
        • They may be found in saltwater, as well as freshwater, and wet soil.
        • They have pseudopodia (false feet) which help to change their shape and to capture engulf food. E.g. Amoeba.
        • Marine forms have silica shells on their surface.
        • Some of them such as Entamoeba are parasites.

      • Flagellated protozoans:
        • As the name suggests, the members of this group have flagella.
        • They can be free-living as well as parasitic.
        • Trypanosoma species can spread some dangerous diseases such as sleeping sickness.


      • Sporozoans:
        • This includes diverse organisms that have an infectious spore-like stage in their life cycle.                
        • The most notorious is Plasmodium (malarial parasite) which causes malaria which has a staggering effect on human population.