Classification of Protozoa
- The sub kingdom Protozoa which was originally included in the kingdom protista includes unicellular, non-photosynthetic, eukaryotic microorganism that are considered single celled, The Protozoan Animals.
- The Protozoa may be defined as ‘microscopic, acellular animalcules existing singly or in colonies without tissues and organs, having one or more nuclei.
- When in colonies, they differ from metazoa in having all the individuals alike except those engaged in reproductive activities.
- The classification followed here is given by the committee on Taxonomy & Taxonomic problems of the society of protozoologists (Honigberg et al. 1964).
- According to Honigberg et al., (1964) Protozoa have been classified into four subphyla.
Sub Phylum I- Sarcomastigophora
- Organelles of locomotion are pseudopodia or flagella.
- Nucleus is of single type (monomorphic).
- There is no spore formation.
- Syngamy occurs in reproduction.
Super class Mastigophora
- They are commonly called flagellates.
- Organelles of locomotion in adults are flagella.
- Body is covered by pellicle.
- Binary fission is longitudinal.
- They are mostly free-living though some are parasitic.
Class 1 Phytomastigophora
- They generally possess chromatophores.
- There are usually only one or two flagella.
- The nucleus is vesicular.
Order 1 Chrysomonadina: Examples: Chromulina, Ochromonas, Chrysamoeba
Order 2 Coccolithophorida: Examples: Coccolithus, Rhabdosphaera.
Order 3 Heterochlorida: Examples: Heterochloris, Myxochloris
Order 4 Cryptomonadida: Examples: Chilomonas, CnJPtomonas
Order 5 Dinoflagellida: Examples: Noctiluca, Ceratium
Order 6 Euglenida: Examples: Euglena, Peranema
Order 7 Volvocida: Examples: Volvox, Eudorilla
Class 2 Zoomastigophora (Zoomastigina)
- They have no chromatophores.
- There are one to many flagella.
- Often there is an undulating membrane.
- Most of them are parasitic.
Order 1 Choanoflagellida: Example: Proterospongia
Order 2 Rhizomastigida: Examples: Mastigamoeba, Dimorpha
Order 3 Hypermastigida: Examples: Trichonympha, Leptomonas
Order 4 Diplomonadida: Examples: Giardia, Hepamita
Order 5 Kinetoplastida
Sub order 1. Bodonina: Example: Bodo
Sub order 2 Trypansomatina: Examples: Trypanosoma, Leishmania
Order 6 Bicosoecida: Examples: Salpingoeca, Poteriodendroll
Order 7 Retortamonadina: Example: Chilomonas
Order 8 Oxymonadina: Examples: Oxymonas, Pyrsonympha
Order 9 Trichomonadina: Example: Trichomonas
Super class B Opalinata
- They have numerous cilia-like organelles in oblique rows over the entire body surface.
- There is no cytostome.
- Binary fission is interkinetal.
- There is syngamy with flagellated gametes.
- All are parasitic.
Super class C. Sarcodina
- Their organelles of locomotion are pseudopodia.
- The amoeboid form is predominant.
- Some have a hard shell.
- They generally do not form spore.
- Formation of gametes and flagellated young ones are common.
Class 1 Rhizipodea
- Their organelles of locomotion are pseudopodia or filopodia but never axopods.
- They are generally creeping forms.
Sub Class (i) Lobosia
- Pseudopodia are typically lobose rarely filiform or anastomosing.
Order (1) Amoebida: Examples: Amoeba, Pelomyxa, Entamoeba
Order (2) Arcellinida: Examples: Arcella, Difflllgia
Sub class (ii) Filosia
- They have tapering and branching filaments rarely anastomosing.
Examples: Gromia, Allogromia
Sub class (iii) Granuloreticulosia
- They have finely granular reticulose podia (reticulopodia).
Order (1) Foraminiferida: Examples: Globigerilla, Elphidium
Sub class (iv) Mycetozoia
- The amoeboid trophic stage develops either into a multicellular aggregation or into a true multinucleate plasmodium.
- Life cycle complex & has sexual reproduction.
- Usually, sporangia are formed which liberate spores.
- Nutrition is phagocytic.
Class 2 Piroplasmea
- Small, round, rod-shaped or amoeboid parasites in vertebrate red blood cells.
Class 3 Actinopodea
- Their organelles of locomotion are delicate and radiose axopodia.
- They are primarily sessile or floating forms.
- Test is present or absent.
- Gametes are usually flagellated.
- Reproduction is both sexual and asexual.
Sub class 1 Radiolaria
- Central capsule is perforated by one to many pores.
- They have spicules or a siliceous skeleton.
- Filopodia or axopodia are present.
- The capsule separates the protoplasm into ectoplasm & endoplasm.
- All are marine.
Examples: Thalassicola, Collozollm, Lithocircus
Sub class 2 Acantharia
- Imperforate, non-chitinoid central capsule without pores.
- Anisotropic skeleton of strontium sulphate.
Sub class 3 Heliozoia
- There is no central capsule.
- Rounded body with radiating axopodia.
- Usually naked, if a skeleton is present it is made of siliceous scales and spines.
- They have axopodia or filopodia.
- There may be more than one nucleus, mostly in fresh water.
Examples: Actinophnjs, Actillosphaerlum, Clathrulina
Sub class 4 Proteomyxidia
- Largely marine and freshwater parasites of class and higher plants.
- Filopodia and reticulopodia in some species.
Sub Phylum II- Sporozoa
- The adult has no external organelles of locomotion.
- They are all parasitic and incapable of active life outside their hosts.
- Cilia or flagella may be present in gametes.
- Syngamy takes place after which many spores are formed.
- The spores are simple and contain one to many sporozoites.
- Sporozoites are the infective phase.
- Nucleus is of the single type.
Class 1 Telosporea
- Pseudopodia are generally absent & locomotion is by gliding or body flexion.
- Spores are formed & there are flagellated microgametes in some.
- Reproduction is both sexual & asexual.
Sub class I Gregarinia
- Mature trophozoites are large and extracellular.
- Reproduction is entirely sexual with sporogony.
- The spores contain eight sporozoites.
- They are parasites in the digestive tract and body cavity of invertebrates.
Sub class 2 Coccidia
- Mature trophozoite is small & typically intracellular.
- Being parasitic in the digestive tract or blood.
- Gametocytes are dimorphic.
- Sporozoites multiply by schizogony in tissue cells.
Order (a) Eucoccida
- Schizogony takes place.
- There are both sexual & asexual phases in the life cycle.
- They are parasitic in epithelial and blood cells of invertebrates and vertebrates.
Sub order 1 Eimeriina Examples: Eimeria
Sub order 2 Haemosporina Examples: Plasmodium
Class 2 Toxoplasmea
- Spores are absent.
- There are no flagella or pseudopodia at any stage.
- Reproduction by binary fission.
- Cysts are formed which have many naked sporozoites.
Examples: Sarcocystis, Toxoplasma
Class 3 Haplosporea
- Spores are present.
- Pseudopodia may be present but flagella are absent.
- Reproduction is only asexual & schizogony takes place.
Sub Phylum III- Cnidospora
- Spores have several cells having one or more polar filaments which are coiled threads and can be shot out, and one or more sarcoplasma or sporoplasma.
- All are parasitic.
- Zygote gives rise to one or more trophozoites without sporogony.
Class 1 Myxosporidea
- Spores are of multicellular origin.
- There are one or more sporoplasms, with two or three valves.
- They are parasitic in fishes.
Examples: Myxobolus, Ceratomyxa
Class 2 Microsporidea
- Spores are of unicellular origin.
- There is one long tubular polar filament through which the sporoplasm emerges, one valve only.
Sub Phylum IV- Ciliophora
- All possess simple ciliary organelles for locomotion, infraciliatureis subpeculiar.
- They have two nuclei, a trophic macronucleus and a reproductive micronucleus.
- Binary fission is perkinetal.
- Conjugation takes place with fusion of nuclei, autogamy and cytogamy also occur.
- There are never any free gametes.
- Nutrition is mixtrophic or heterotrophic.
- They usually have a cytostome.
Class 1 Ciliatea
- All possess cilia or compound ciliary structure as locomotor or food acquiring organelles at some time in the life cycle.
- Also present is an infraciliary system, composed of basal granules below the cell surface and interconnected by longitudinal fibrils.
- Most ciliates possess a cell mouth or cytostome.
- Two types of nuclei, one vegetative (macro-nucleus) and the other reproductive (micronucleus).
- Fission is transverse.
- Sexual reproduction never involves the formation of free gametos.
Sub class I. Holotrichia
- With simple or uniform body cilia.
- Buccal ciliature either absent or, if present, usually inconspicuous.
Order 1 Gymnostomatida Examples: Coleps, Dileptus, Didillium
Order 2 Trichostomatida Examples: Colpoda, Balantidium
Order 3. Chonotrichida Examples: Spiroclwna, Chilodochona
Order 4. Apostomatida Examples: Nassula
Order 5 Astomatida Examples: Anoplophyra, Hoplitophyra
Order 6 Hymenostomatida Examples: Colpidium, Tetrahymena, Paramecium
Order 7 Thigmotrichida Examples: ThigmophnJa, Boveria
Sub Class II Peritrichia
Order 1 Peritrichida Examples: Vorticella, Trichodina
Sub Class III Suctoria
Order 1 Suctorida Examples: Acineta, Ephelota
Sub Class IV Spirotrichia
- With generally reduced body cilia.
- Well developed conspicuous buccal ciliature.
Order 1 Heterotrichida Examples: Bursaria, Stentor, Spirostonlunl, Nyctotherus
Order 2 Oligotrichida Example: Halteria
Order 3 Tintinnida Examples: Codonella, Favella
Order 4 Entodiniomorphida Examples: Elltodiniunl, Cyclopostltill1n
Order 5 Odontostomatida Example: Saprodilli
Order 6 Hypotrichida Examples: Euplotes, Stylonychia, UroshJla, Oxytricha
Brief Classification of the Parasitic Protozoa
Parasitic protozoa are classified mainly into four groups. They are:
(a) Rhizopoda (Plasmodroma)
The organisms of this group move by producing pseudopodia. They multiply by binary fission and form cysts, as in E. histolytica.
The organisms move by means of flagella, binary fission takes place by longitudinal division e.g., Trypanosoma, Leptomonad etc.
They move by amoeboid movement with a change in form and position and they have no organ of locomotion. These organisms multiply by the process of schizogony within the vertebrate host and sexually by the method of sporogony (reduction division).
Fusion of gametes is followed by sporozoite formation in a sporocyst as in the invertebrate host e.g. Anopheles mosquito in human malaria caused by Plasmodium vivax, P. ovale, P. malaria, P. falciparum.
(d) Ciliophora (Ciliates)
The organisms move by cilia and multiply by transverse division of the body. They also produce cysts, e.g. only pathogenic species is Balantidium coli.
- Trivedi P.C., Pandey S, and Bhadauria S. (2010). Textbook of Microbiology. Pointer Publishers; First edition
- Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi : Jaypee Brothers Medical Publishers.
- https://www.cliffsnotes.com/study-guides/biology/microbiology/the protozoa/classification-of-protozoa