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In this article we will discuss about the definition and classification of protozoa.
Definition of Protozoa:
Protozoa are minute animalcules visible only under the microscope. About 50,000 species are known so far. A protozoan is an independent eukaryotic cell i.e. a complete unicellular organism.
The branch of study is called Protozoology. It was Leeuwenhoek (1677) who first of all studied “protozoa” but its name was given by Goldfuss (1817). Locomotion takes place through pseudopodia, flagella or cilia. Nutrition principally heterotrophic, some are autotrophic.
They are unicellular eukaryotic microorganisms, lack cell walls, colourless and motile. They are larger than prokaryotes but lack chlorophyll. They obtain food by ingesting other organisms found in fresh water of ponds, pools, ditches, etc.
Some are marine but majority of them are parasitic in other animals, including humans. Some are found in soil. The uptake of nutrients (macromolecules) occurs by a process called pinocytosis.
Most of them also ingest the food by phagocytosis, but some form special structure called gullet. The mechanisms of their motility divides into taxonomic groups e.g. Sarcodina in which movement occurs by amoeboid motion, those using flagella i.e. Mastigophora. The protozoans use cilia belong to Ciliophora while non- motile and parasitic to higher animals belong to Sporozoa.
Classification of Protozoa:
Phylum Protozoa is divided into four subphyla based on locomotory organs.
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Subphylum A: Sarcomastigophora:
In these cases, the locomotory organelles are pseudopodia or flagella or both. There is presence of one nucleus or more nuclei in organism. There are three classes.
Class – 1:
Mastigophora or Flagellata
Class – 2:
Sarcodina or Rhizopoda
Class – 3:
Opalinata
Subphylum B: Sporozoa (= Apicomplexa):
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All the organisms are endoparasites. No specialized locomotory organelles and contractile vacuoles are present but possess an apical complex of ring like, tubular, filamentous organelles at apical end at some stage of their life-cycle. The life cycle of such organisms is complicated, spores usually formed but have no polar filaments. The sporozoans are divided into two classes on the basis of sporozoites (contained spores).
Class – 1:
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Telosporea
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Class – 2:
Piroplasmea
Subphylum C: Cnidospora (= Microspora):
They are intracellular endoparasites, especially on insects. No locomotory organelles and contractile vacuoles are present. The spores are formed but these differ from sporozoams in possessing one to four polar filaments. Cnidiospora is divided into two classes on the basis of their mode of spore formation.
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Class – 1:
Myxosporea
Class – 2:
Microsporea
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Subphylum D: Ciliophora:
This is the largest group of protozoans which are animal-like and structurally complex. The locomotory organelles are cilia or ciliary organelles; cilia are replaced in the adult by sucking tentacles for feeding.
A single large-macronucleus of trophic function and one to several small micronuclei of reproductive function are present. The reproduction is mainly by asexual means (transverse fission) and occurs sexually by conjugation.
Class 1:
Ciliata:
There is only one class in this subphylum.
