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2. Phylum - Protozoa

2.1 Introduction

  • The study of protozoans is termed as protozoology.

  • Protozoa is the 3rd largest phylum in which 30,000 species are present.

  • In this phylum unicellular and heterotrophic organisms are included.

  • These one-celled body performs all the biological-activities like multicellular animals. So these are termed as “Acellular-Noncellular” organisms. (term by Dobell)

  • Protozoan animals were first studied by “Leeuwenhoek”.

  • The word protozoa was first used by - “Goldfuss”.
  • Rhizopoda given by Dujardin
  • Ciliata given by Perty
  • Sporozoa is given by Leuckart
  • Leder-Muller “termed protozoa as “Infusoria”. Because they are found in debris.

2.2 General Characters

  • Habitat - Protozoans are universal and cosmopolitan in distribution. The animals of this phylum are free living or parasites in plants or animals these are solitary or colonial.

  • Habit - These are the simplest microscopic and most primitive animals.

  • Organisaton - “Protoplasmic level’’. Their shape is of different types ie. irregular, elongated or round. Body is unicellular which has one or more nucleus which may be monomorphic or Dimorphic.

    Unicellular body performs all the necessary biological activities, so in them subcellular - physiological division of labour is found.

  • Exoskeleton - The body of most animals is naked and some have Pellicle, test or shell on their body as exo-skeleton. On the body of some protozoans an exoskeleton of or silica is found e.g.
    Radiolaria & Foraminifera group.

  • Locomotion - In them many types of locomotary organs are found. Finger like pseudopodia, cilia, flagella, tentacles or absent.

  • Nutrition - Nutrition is of different types, like Holozoic, Holophytic, Mixotrophic like in euglena, Parasitic in plasmodium sparozoic. These have cytostome and cytopyge e.g. Paramecium or These may be absent. Digestion is intracellular and it takes place in the food vacuoles.

  • In these, excretory and respiratory organs are absent. Both these processes take place through general body surface, and by the process of simple-diffusion. These are Ammonotelic animals.

  • Protozoans which are found in fresh water they may have one or more contractile - vacuoles for water-balance or osmoregulation. e.g. Amoeba has 1 contractile - vacuole - Paramecium has 2.”

  • Reproduction - Reproduction may be sexual or asexual. Asexual reproduction is more common ; and takes place by ‘binary fission, Budding or Multiple-fission. Sexual reproduction takes place by hologamy in adults of paramecium, and by syngamy in plasmodium.

  • Life cycle - Life-cycle is simple in most animals. In some animals alternation of asexual and sexual generations is found eg. Polystometa. They have more capability of encystment for protection from environmental conditions and also for dispersal. They don’t have natural-death because in unicellular animals there is no division of Somatoplasm and germplasm and so these are considered immortal.

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  • Protozoans are classified on the basis of locomotary organelles. It has been divided into 4 sub-phyla:
    • Sarcomastigophora
    • Sporozoa
    • Cnidospora
    • Ciliophora

2. 3 Sub - Phylum : Sarcomastigophora

  • Locomotary organs are pseudopodia or flagella or both,
  • Nucelus one or many and similar type.

    These are divided into 3 classes -

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Class - 1 : Mastigophora or Flagellata

  • Locomotary organs are one or many flagella.

  • Many members have chlorophyll e.g. Euglena.

  • Their body has pellicle so they have a definite shape.

  • Nucleus one.

  • Binary fission is longitudinal. Sexual Reproduction is absent.

  • Contractile - Vacuole is present for Osmoregulation.

  • Nutrition is mixotropic.

  • Example:

    • Euglena
    • Proterospongia : This is a colonial protozoan. It is a connecting link between protozoa and porifera.
    • Mastigamoeba : It is a connecting link between mastigophora and Sarcodina.

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  • Leishmania donovani : This parasite is responsible for kala-azar disease in man.

    • This disease spreads through sand - fly (phlebotomus).
    • This parasite is dimorphic and digenetic. Disease caused by it is also known as “Dum-dum fever” or visceral Leishmaniasis or Tropical splenomegaly. (L. Tropica causes – Delhi Boils or oriental sores disease.)
  • Trypanosoma gambiens : This parasite causes “African sleeping sickness” in man-This disease spreads through Tse-Tse fly (Glossina palpalis/tachinoides) . T. gambiens is polymorphic-Leptomonad form, crithidial form, Trypanosomal forms.

  • Trypanosoma cruzi : It causes disease Chagas.

  • Giardia intestinalis : It is termed as Grand-old man of Intestine”. It causes diarrhoea in humans.

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  • Trichomonas vaginalis : It is a parasite in the vagina. It causes “Vaginitis = Leucorrhoea”.

  • Trichonympha : This is a symbiont in the intestine of termite and wood cockroach. It helps in the digestion of cellulose.

  • Noctiluca : It shows bioluminiscense due to Luciferin protein. It is also called the Fire of Sea”.

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Class - 2 : Sarcodina or Rhizopoda

  • Locomotary organs are organs that help in locomotion different types of pseudopodias are:-

    • Lobopodia - in Amoeba
    • Filopodia - in Euglypha, Chlamydophorus
    • Reticulopodia - in Globigerina
    • Axopodia - in Actinophyrus, Actinosphaerium.
  • Body is naked so shape is changeable, few have different types of shells.

  • Pseudopodia help in feeding and locomotion.

  • Nutrition is Holozoic or Saprozoic or others.

  • Cytoplasm is divided into Ectoplasm and Endoplasm.

  • Nucleus is one or many but monomorphic.

  • Animals may be free-living or parasitic.

  • Contactile vacuole found in only fresh water species like amoeba. But in parasites and marine-animals the contractile-vacuoles are absent. e.g. Entamoeba histolytica

  • Asexual reproduction normally takes place by Binary-fission, which is transverse Sexual reproduction is absent.

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  • Example :

    • Amoeba Simplest animal
    • Pelomyxa - chaos This is the largest amoeba. Size = 6 mm. It is multinucleated.
    • Entamoeba histolytica - It is a parasite in the colon of man. It causes amoebic dysentery in man. In it contractile vacuoles are absent. It is dimorphic:-

      • Magnum-Pathogenic
      • Magnum-Pathogenic
    • Entamoeba gingivalis - It is found in between the teeth of man. It increases Pyrea disease but does not cause it. Pyrea is caused by “Trichomonas-tinax”.

    • Arcella - It has an exoskeleton of tectin.
    • Elphidium (Polystomella) - It has a multichambered shell of silica and magnesium sulphate.
    • Thalassicola shell
    • Acanthometra shell
    • Allogromia - It has internal skeleton.

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  • Actinophrys - It is termed as the “Sun aninmalcule”.
  • Entamoeba coli - It is found in the intestine of man. It shows commensalism.
  • Aulocantha - It have maximum chromedia.
  • Radiolarian

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Class - 3 : Opalinata or Protociliata

  • Locomotory organs are flagella which are found on the whole surface of body.
  • Body has pellicle over it.
  • Nuclei many but isomormphic.
  • Binary fission common, sexual reproduction takes place by syngamy.
  • Contractile-vacuole is absent.
  • All flat and parasite in the intestine of amphibia.
  • Cytostome absent.
    e.g.Opalina” - It is found as a parasite in the intestine of frog.

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2.4 Sub Phylum - 2 : Sporozoa


  • All the members of this group are endoparasite. These are found in cells (called cytozoic) tissues (called histozoic) or in vacuoles (called coelozoic).

  • Locomotory organs are absent.

  • A thick pellicle is present on the body.

  • Cytostome, cytopyge and contractile vacuoles are absent.

  • Binary-fission absent, In place of that asexual reproduction takes place with the help of multiple fission.

  • Sexual reproduction takes place by syngamy. Spore formation takes place in most of the members.

  • Life-cycle is complex. Polar filaments are absent in spores.

  • Sub-phylum sporozoa is divided into four classes on the basis of presence or absence of spores in life cycle.

Class 1: Telosporea

  • Sporozoites elongated and mostly find in spores


  • Plasmodium - Four species spread malaria fever in human. Female anopheles is the carrier of plasmodium. P. falciparam causes “Malignant Malaria” or “Black water fever” or “Cerebral Malaria”.

  • Monocystis - It is found in seminal vesicle of earthworm, and causes sterility in earthworm. It is
    monogenetic in nature.

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  • Eimeria - It is found in epithelial cells of liver of rabbit.

Class - 2 : Piroplasmea

  • Microscopic parasites of the RBC of animals in which spores are not formed, the sporozoites are naked.


  • Babesia - It causes the “Texas cattle fever” in animals. This disease also called “Red water fever” or “Haemoglobin-uric fever”.

Class - 3 Toxoplasmea & Sarcocystis

  • Example : Toxoplasma & Sarcocystis

Class - 4 Haplosorea

  • Example : Coelosporidium.

2.5 Sub Phylum - 3 : Cnidospora

  • Parasites of other animals like sporozoa.
  • Absence of locomotary organs and contractile vacuoles.
  • Spore-formation takes place in life-cycle the spores have polar - filaments.
  • Cnidospora has been classified into 2 classes on the basis of development of spores

Class 1 - Mixosporea

  • Spores develop from many nuclei. Spore shell made of 2 or 3 valves. Example - Ceratomyxa, Myxidium.

Class 2 - Mictrosporea

  • Spores develop from 1 nucleus. Spore shell made of only 1 valve.

    Example : Nosema - It is an endoparasite of the tissues of silk-worm. It causes harm to “Sericulture”. This disease is called “Pebrine disease”.

2.6 Sub Phylum - 4 : Ciliophora

  • These are complex protozoa.
  • In at least one stage of life cycle cilia are present for locomotion & feeding.
  • Nuclei are dimorphic or two types the larger one is Macronucleus (vegetative nucleus) and the smaller is Micronucleus (generative nucleus).
  • Body surface has a rigid-pellicle.
  • Asexual reproduction by Binary fission and sexual reproduction by Conjugation. Ciliophora is divided into two classes ciliata and suctoria.

Class 1 - Ciliata

  • Life-cycle is complex. A rigid-pellicle is found around body.
  • Locomotary organs are cilia and present on the whole body surface
  • Nutrition is Holozoic.
  • Nuclei are dimorphic. i.e. Macro nuclei or vegetative and micro nuclei or generative
  • Asexual reproduction takes place by transverse binnary fission and sexual reproduction takes place by Conjugation, Autogamy, Hemimixis, Endomixis and Cytogamy
  • Two contractile - vacuoles are found; present at the anterior and posterior ends of the body. These help in osmo-regulation.
  • For the ingestion and egestion of food permanent pores are present. For ingestion cytostome is present and for egestion cytopyge or cytoproct are also cell-anus is present.
  • Below the pellicle, “Trichocysts” are found which are defence organelles.
  • Paramecium : It is termed as the “Slipper-animalcule”. In the cytoplasm of paramecium some toxic particles are found called “Kappa particles” and “Sigma particles”. Both these particles shown cytoplasmic inheritance Kappa-particles produce “Paramecin which destroys the sensitive species. Paramecium which have Kappa-particles are called killer and which don’t have them are called Non-Killer. Lambda, Mu, Pi particles are also present in cytoplasm. They are transferred to next generation by cytoplasmic inheritance.

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  • Vorticella : It is called “Bell animalcule. It is a pedicellate protozoan.

  • Didinium : It is called “Water-Bear”.

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  • Spirostomum : It is the largest living ciliate. It is 4 mm long.

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  • Balantidium coli : This parasite cause ulcer in the colon of man and causes diarrhoea.
  • Nyctotherus : It is a parasite in the rectum of frog. It is also found in the rectum of cockroach.
  • Neummulites : In the form of fossils largest member of protozoa.
  • Stentor

Class 2 - Suctoria

  • The members of this class are sessile and stalked.
  • Locomotary organs in adults are the “Sucking-tentacles.”
  • Pellicle is found.
  • Cytostome and cytopyge are absent.
  • Asexual reproduction by external budding.
  • Binary fission is absent.
  • Nuclei are dimorphic i.e. a macronucleus and micronucleus are present, but the macronucleus is branched.
  • Only 1 contractile vacuole is present. Example - Arcineta, Ephelota

2.7 Curios

  • Largest protozoa - Pelomyxa Palustris - 1.4 cm long.
  • Longest live protozoa - Euglena gracilis - 20 years.
  • Paramecium bursaria possesses green algae.
  • Fastest running protozoan is “Monas steigmata”.
  • Some protozoans have a loose exoskeleton called “Loricahourse” on them e.g. Difflugia, Tintinn opsis.
  • The fastest reproducing protozoan is “Glaucoma”. It produces 6-generation within 24 hrs.
  • Ceratium” and “Noctiluca” show bio-luminescense.
  • The largest euglena is “E. oxyuris”.
  • When Euglena is kept in dark, then its chlorophyll disappears.
  • “Heliozoans” are mainly fresh water rhizopods and termed “Sun - animalcules.”.
  • Oblique binary fission in ceratium.
  • Ceratium and Notiluca are bioluminiscent due to presence of luciferin protein.

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2.8 Comparison between three classes of Protozoa

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