Phylum: protozoa

  • First animals, solitary or colonial and protoplasmic grade of organization.
  • Simple, unicellular microscopic organisms.
  • Generally free living found in fresh water, salt water and damp soil.
  • Some are parasitic and commensal.
  • Body is naked or covered by pellicle, exoskeleton or internal skeleton may be present in some forms.
  • Locomotory organs are pseudopodia, whip-like flagella and hair like cilia in some forms and absent in sporozoa.
  • Protoplasm divided as ectoplasm and inner endoplasm.
  • Nutrition is holophytic, holozoic and parasitic.
  • Digestion is intracellular and occurs in food vacuoles.
  • Respiration by diffusion through general body surface.

What is Protozoa? - Classification, Characteristics, Examples and Diseases  Caused by Protozoa

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  • Excretion by general body surface, temporary opening in the ectoplasm, permanent opening called cytopyge or contractile vacuoles.
  • Reproduce asexually as well as sexually.
  • Sexual reproduction by conjugation of adults (hologamy), or by fusion of gametes (syngamy).
  • Life cycle complicated with alternation of generation.
  • Resistant cysts formation under unfavourable condition and also for dispersal.

They are classified into four sub-phylum. They are:

Protozoa- Definition, Characteristics, Classification, Examples


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Sub-phylum: Sarcomastigophora

  • Presence of both flagella and pseudopodia for locomotion.
  • Only one type of nucleus (monomorphic).
  • No spore formation.
  • Sexual reproduction by syngamy.
  • It includes three super classes.
  • Examples: Euglena, Ceratium, Trypanosoma, etc.

Sub-phylum: Sporozoa

  • Locomotory organs are absent in adult stage.
  • All are parasitic.
  • Cilia or flagella may be present in gametes.
  • Sexual reproduction occurs by syngamy.
  • The spores are simple and contain one to many sporozoites.
  • The sporozoites are infective phase.
  • The nucleus is only one type.
  • It includes three classes.
  • Examples: Plasmodium, Nematocystis, Toxoplasma, Sarcocystis, etc.

Protozoa- Definition, Characteristics, Classification, Examples

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   Sub-phylum: Cnidospora

  • Spores are multicellular.
  • All members are parasitic in cold blooded vertebrates and in invertebrates.
  • Zygotes give rise to one or more trophozoids without sporogony.
  • It includes two classes.
  • Examples: Ceratomyxa, Nosema, etc.

   Sub-phylum: Ciliophora

  • Have rows of cilia.
  • Unique nuclear dimorphism i.e two types of nuclei are present.
  • Nuclei are micronucleus and macronucleus.
  • Possess a cell mouth or cytostome.
  • Specialized superficial zone of cytoplasm is called pellicle.
  • It includes only one class.
  • Examples: Paramecium, Coleps, Colpidium, etc.




Phylum: protozoa