Protozoans and its classification

  • The word Protozoa is derived from two Greek words: protos means first; zoon means animal.
  • They are the first animals with a protoplasmic grade of body organization.
  • They are simple, unicellular microscopic organisms which may be solitary or colonial.
  • All the vital activities are performed by a single cell so no physiological divison of labour occurs.
  • The body is naked or covered by pellicle and in some cases may be exoskeleton or internal skeleton present.
  • Various kinds of locomotory organs are present such as pseudopodia in Sarcodina, whip-like flagella in Flagellate and hair-like cilia in ciliate and locomotory organs absent in case of sporozoa.
  • The protoplasm is divided as outer ectoplasm and inner endoplasm.
  • Nutrition is holophytic (plant-like), holozoic (animal) or parasitic.
  • Digestion is intracellular and occurs inside food vacuoles.
  • Respiration occurs through the general body surface by diffusion.
  • Excretion occurs through general body surface, a temporary opening in the ectoplasm or through the permanent pore called the cytopyge, or contractile vacuoles.
  • Reproduction is sexually or asexually.
  • Sexual reproduction by conjugation of adults or by fusion of gametes.
  • Life cycle is often complicated with alternation of generation.
  • Formation of resistant cysts occurs to overcome unfavourable conditions as well as to help in dispersal.

They are diverse group of organisms with four sub-phylum. They are:

A) Sub-phylum: Sarcomastigophora

  • It is characterized by the presence of both flagella or pseudopodia for locomotion.
  • They possess only one type of nucleus.
  • There is no spore formation.
  • Sexual reproduction occurs by syngamy.
  • It is classified into three super classes: Mastigophora, Opalinata and Sarcodina.
  • e.g.,Euglena, Ceratium, Chilomonas, etc.

Image result for euglena    Image result for ceratium


B) Sub-phylum: Sporozoa

  • Locomotory organs are absent in adult stage.
  • All are parasitic forms.
  • 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 the infective phase.
  • The nucleus is of only one type.
  • It is classified into three classes: Telosporea, Toxoplasmea and Halosporea.
  • e.g., Plasmodium, Nematocystis, Caelosporidium, etc.

Image result for plasmodium       Image result for toxoplasma


C) Sub-phylum: Cnidospora

  • Al members are parasitic in cold- blooded vertebrates and in invertebrates.
  • Spores are multicellular.
  • Zygote gives rise to one or more trophozoids– without sporogony.
  • It includes two classes: Myxosporidea and Microsporidea.
  • e.g.,Ceratomyxa, Nosema, etc.

Protozoa- Definition, Characteristics, Classification, Examples                                                                                   Image source: biologynotes


D) Sub-phylum: Ciliophora

  • They have rows of cilia, the unique nuclear dimorphism i.e. two types of nuclei are present: macronucleus and micronucleus.
  • Most ciliates possess a cell mouth or cytostome.
  • It includes only one class: Ciliata.
  • e.g.,Paramecium, Coleps, Colpedium, etc.


Image result for paramecium Image result for ceratomyxa




Protozoans and its classification