Protos—first, Zoan—animal, First animal phylum
Study of protozoans called Protozoology
Father of protozoology – Antony von Leeuwenhoek
Term Protozoa was assigned by Goldfuss
Protozoa belong to Kingdom Protista of Haeckel
Single-celled, solitary or colonial, eukaryotes
Important characters
- Size ranges from 1µ to 5000µ
- Aquatic – freshwater or marine forms, or endoparasites
- Grade of organization– protoplasmic or subcellular
- Locomotion by cilia, flagella or pseudopodia, or absent
- Skeleton – may or may not be present; if present then either calcareous or siliceous. Foraminifers have external shell of CaCO3 ( ex. Polystomella), whereas Radiolarians have internal plates of silica
- Osmoregulation by contractile vacuole in freshwater protozoans (isotonic to 0.8 % NaCl solution). C.V. absent in parasitic and most of the marine forms.
- Symmetry—radial, bilateral or absent (asymmetrical)
- Nutrition—Holozoic or holophytic.
- Digestion intracellular within food vacuole. Reserve food material- Glycogen or Starchlike bodies
- Respiration – exchange of gases occurs through plasma membrane
- Excretion –excretory product NH3 (Ammonotelic). Excretion occurs through general body surface or plasmalemma.
- Blood and nervous tissue absent. Sensory structure stigma (eyespot) present in Euglena
- Reproduction – Asexual or Sexual. Asexual by budding, spore formation, binary fission or multiple fission. Sexual by Conjugation (Paramecium) or gamete formation (Plasmodium)
Classification
Basis of classification – Locomotory structures
1. Sub Phylum Sarcomastigophora
(i) Super Class Mastigophora (Flagellata) —
- Locomotory structures- flagella
- Most primitive class
- Binary fission –longitudinal
Two subdivisions- Phytomastigophora and Zoomastigophora
| Phytomastigophora | Zoomastigophora |
|---|---|
| Green | Non-green |
| Chloroplast present | Chloroplast absent |
| Mostly free living | Mostly parasites |
| Reserve food material –starch (paramylon bodies) | Reserve food material –Glycogen |
| Flagella- 1 to 2 | Flagella 1 to many |
| ex. Euglena, Volvox, Noctiluca and Ceratium Noctiluca –shows bioluminescence, called Burning of sea | ex. Trypanosoma , Leishmania , Giardia, Trichomonas, Trichonympha, Proterospongia, Mastigamoeba |
T. brucei—digenetic parasite, primary host-cattle and secondary host – a fly; Disease-Nagana
T. cruzi—digenetic parasite, primary host- man and secondary host – dipteran fly; Disease- Chagas
T.evansi—digenetic parasite, primary host –horse and secondary host – Horsefly (Tabanus); Disease- Surra (skin disease)
Trichomonas – T. tenax aggrevates pyrrhoea, T. vaginalis causes leucorrhoea.
Leishmania donovani— a digenetic parasite, primary host- man and secondary host – Sandfly(Phlebotomus); Disease- Kala-azar(Dumdum fever)
L. tropica—causes Oriental sore or Skin Leishmaniasis
Giardia— a bilaterally symmetrical form, commonly called ‘Grand old man of intestine’; causes Diarrhoea
Trichonympha – It is a symbiotic protozoan in the gut of termites, for cellulose digestion.
(ii) Super Class Sarcodina (Rhizopoda)-
- Locomotory structures-Pseudopodia ( false legs)
- Free living or parasitic forms
- Includes Heliozoans, foraminifers, radiolarians and amoebids
ex. Amoeba, Entamoeba, Polystomella, Arcella, Pelomyxa and Babesia (an RBC parasite, transmitted through tick and causes Texas fever in cattles)
Entamoeba histolytia – a monogenetic parasite in colon (large intestine) of man; causes Amoebiasis or Amoebic dysentry. Infective stage – Tetranucleated cyst. Mode of infection – contaminated food and water.
E. gingivalis (or buccalis) – a monogenetic parasite in the pockets, between teeth and gums; aggrevates pyrrhoea. Infective stage – Trophozoite. Mode of infection – Mouth to mouth kissing.
E. coli – a commensal of colon
2. Subphylum Ciliophora (Class Ciliata) –
- The biggest and the most advanced class of protozoa
- Binary fission – Transverse
- Nuclei dimorphic, Micronucleus- reproductive and Macronucleus- vegetative in function.
ex. Paramecium, Vorticella and Rectal ciliates. Rectal ciliates –found in the rectum of frog and toad, include Balantidium, Nyctotherus and Opalina. Opalina has multinucleated condition. (micro- and macronuclei not differentiated).
Though the locomotory structures in Opalina are cilia, due to multinucleated condition, it is sometimes included in superclass Opalinata.
3. Subphylum Sporozoa –
- Locomotory structures absent
- Members most specialized for parasitic mode of life.
- Exclusively endoparasites (contractile vacuole absent)
ex. Plasmodium, Monocystis and Eimeria
Monocystis– endoparasite in the seminal vesicle of earthworms, feeding on sperms
Eimeria– causes coccidiosis in poultry birds
4. Subphylum Cnidospora –
- Spore formation throughout life
- Spores contain polar capsule and coiled filament for attachment
- Trophozoite – multinucleated
ex. Nosema, Myxidium (Nosema bombysis causes ‘Pebrine’ disease in silkworm, Bombyx mori).
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