Introduction
Q.1. Write the general characters of protozoa.
Ans. General characters: -
1. Small, usually microscopic animalcules, ordinarily not visible without a microscope.
2. Simplest and most primitive of all animals, with protoplasmic grade of organization.
3. Body unicellular, containing one or more nuclei which are monomorphic or dimorphic.
4. Solitary or forming loose colonies in which individuals remain alike and independent.
5. Body symmetry none, bilateral, radial or spherical.
6. Body naked or bounded by a pellicle and often provided with simple to elaborate shells or exoskeletone.
7. Body form usually constant, varied in some, while changing with environment or age in many.
8. The single cell body performs all the essential and vital activities, which characterize the animal body : hence only subcellular physiological division of labour.
9. Locomotor organelles are finger-like pseudopodia or whip-like flagella or hairlike cilia or absent.
10. Nutrition holozoic (animal-like), holophytic (plant-like), saprozoic or parasitic. With or without definite oral and anal apertures. Digestion occurs intracellularly inside food vacuoles.
11. Respiration and excretion through general surface or through contractile vacuoles, which serve mainly for osmoregulation.
12. Reproduction asexual by binary multiple fission and budding and sexual by conjugation of adults (hologamy) or by fussion of gametes (syngamy).
13. Life history often complicated with alternation of asexual and sexual phases.
14. Encystment commonly occurs to help in dispersal as well as to resist unfavourable conditions of food, temperature and moisture.
15. Free-living protozoa mostly aquatic, inhabiting fresh and sea waters and damp places. Parasitic and commensal protozoa live over or inside the bodies of animals and plants. Sufficient moisture is essential in their environment.
16. The single-celled individual not diferentiated into somatoplasm and germplasm : therefore, exempt from natural death which is the price paid for the body.
17. About 50,00 known species.
Q.2. Classify protozoa upto orders and mention the characters and suitable examples of each order ? (1999, 2000)
Ans. The phylum protozoa contains about 30,000 known species. These are grouped in two subphyla.
Subphylum 1 Plasmodroma: -
Consists of 3 classes
Class-1 Rhizopoda or Sarcodina
Class-2 Mastigophora and
Class-3 Sporozoa
Subphylum 2 Ciliophora or Infusoria: -
Consist of 2 classes
Class-1Ciliata
Class-2 Suctoria
Characters of the Class Rhizopoda or Sarcodina: -
1. Body naked i.e. not having a firm, delicate pellicle body outline or internal protoplasmic strands.
2. Contractile vacuoles are present except inmarine forms.
3. Generally amoeboid body forms.
4. Locomotion and food engulfing is processed by false feet called psuedopodia, which forms in various shapes as per requirement by the pressure developed due to concentration of protoplasm.
5. Absence of localized mouth.
6. Meganucleus absent.
7. Asexual reproduction by binary fission.
8. The majority of the forms are free living only few are parasitic.
Classification of Rhizopoda: -
About 8,000 species of this class are divided in six orders.
Order 1 - Lobosa (Amoebina): -
1. Presence of short and blunt pseudopodia known as locopodia.
2. The Ectoplasm and Endoplasm are clearly marked.
3. Vacuoles are always absent in ectoplasm.
Order Lobosa is divided into two sub-orders: -
Sub-order 1 - Gymnamoeba or Nuda: -
1. Naked body, without a shell.
2. Cell-membrane is thin, shape constantly changes due to prolongation of pseudopodia from any point of thin layer.
Examples : (i) Amoeba (ii) Entamoeba histolytica (iii) Entamoeba coli (iv) Entamoeba gingivalis (v) Pelomyxa and (vi) Dimastigamoeba.
Sub-order 2 - The camoeba or Testacea: -
1. Body covered by a single shell.
2. Shell covering the body is provided with only one opening called pylome through which pseudopodia extends for locomotion.
Example : Arcella (ii) Lieberkuhnia and Diffugia.
Order 2 Filosa: -
1. Ectoplasm absent.
2. Branched pseudopodia (called filopodia) are present. Example : Englypha.
Order 3 - Foraminifera: -
1. Large-sized mostly marine rhizopods.
2. Fine, branched, recticulate network of pseudopodia is present.
3. Shell is one or many chambered, having single opening (imperforate) or with numerous fine pores (perforate) from where the network of pseudopodia extends.
4. Vacuolated ectoplasm.
Examples : (i) Polystomella (ii) Globigerina (iii) Microgromia and (iv) Allogromia.
Order 4 Heliozoa: -
1. Mostly fresh water spherical rhizopods.
2. The marked division in the body exists between outer vacuolated cortex and an inner denser medulla.
3. From the spherical bodies pseudopodia extends in fine, stiff radiating ray-like form by an axial filament.
4. Some forms are having siliceous spicules. Examples : (i) Actinophrys and (ii)Actinosphaerium.
Order 5- Radiolaria: -
1. Exclusively marine and spherical in shape.
2. Perforated membranous central capsule dividing the cytoplasm into an intra and an extra cellular region is present together with skeleton of siliceous spicules.
3. Small radiating pseudopodia develops. Axial filaments are absent.
4. Ectoplasm have numerous vacuoles. Examples : (i) Acanthometra (ii) Litheircus (iii) Callozoum and (iv) Actinomma,
Order 6- Mycetozoa: -
1. Bddy without shell, skeleton or central capsule. Semi- terrestrial in nature.
2. Amoeboid, large body, multinucleate, forming plasmodia by the flowing together of individuals.
3. Blunt pseudopodia are numerous.
4. Reproduces by Cellulose-coated spores.
Class 2- Mastigophora or Flagellata: -
1. The body usually covered with a fine membrane of pellicle.
2. The special feature is the presence of one or more whip like flagella meant for locomotion and food capture.
3. A single nucleolus (endosome) is present within a nucleus. Meganucleus is absent.
4. Asexual reproduction occurs by longitudinal fission.
5. Free living solitary or colonial. Many are human or animal parasites.
The class Mastigophora is divided into two sub-classes
Sub-class 1 - Phytomastigina: -
1. Mastigophora possessing chromatophores.
2. Holophytic or plant-like nutrition by the process of photosynthesis in sun-light.
3. Flagella are usually two.
4. Reserve food material is starch or other amyloid substances.
5. Parabasal bodies are absent.
6. Syngamy generally takes place.
Sub-class Phytomastigina contains six orders: -
Order 1- Chrysomonadina: -
1. Small flagellates with a thin cuticle generally amoeboid in shape.
2. 1 or 2 flagella present can be marked as principal and accessory flagellum.
3. Gullet or mouth is absent.
4. 1 or 2 yellowish or brownish chromatophores are present.
5. Nutrition usually like plants i.e. holophytic, but sometimes saprophytic or holozoic.
6. Reserve products are oil and leucosin, starch is absent.
7. Sometimes Calcareous or silicious skeletal structures are present. Examples (i) Chrysamoeba (ii) Synura (iii) Ochromonas (iv) auroglena (v) Dinobryon and (vi) Chromulina.
Order 2- Cryptomonadina: -
1. Small flagellates with a difinite cuticle amoeboid form is rare.
2. A gullet or mouth is present.
3. Unequal 1 or 2 flagella present.
4. Differently coloured two chromatophores are usually present, which can be absent.
5. Mostly holophytic nutrition, but sometimes saprophytic.
6. Reserce food material is starch and often oil also. Examples : (1) Cryptomonas, (ii) Chilomonas and (iii) Cyathomonas etc.
Order 3- Euglenoidine: -
1. Large flagellate with a thick and stout cuticle.
2. Anterior end with cytopharynx or mouth (gullet).
3. 1 or 2 flagella, arising from the anterior depression.
4. Several green chromatophores are present or may be absent.
5. Nutrition is holophytic if green chromatophores (chlorophyll) is present or may be saprophytic or holozoic.
6. Reserve food material is paramylum and oil.
7. A red-spot or stigma and a contractile vacuole is present at the anterior end of the body. Examples : (i) Euglena (ii) Peranema (iii) Copromonas and (iv) phacus.
Order 4 - Phytomonadina or Volvocina: -
1. Flagellates similar to algae having rigid cellulose covering.
2. Transverse groove or gullet is absent.
3. Number of flagella present is usually 2, but can be 1 or 4 or even more rarely.
4. Green or brown chromatophores are present.
5. Holophytic or saprophytic nutrition.
6. Reserve food material is starch and oil.
7. Red-spot present. Examples : (i) Chlamydomonas (ii) Volvox (iii) Pandorina and (iv) Haematocoecus
Order 5 - Chloromonadina:-
1. Small flagellated having delicate cuticle, amoeboid in form.
2. Gullet present but transverse groove is absent.
3. Two flagella are present.
4. Chromatophores are numerous, green coloured or sometimes colourless.
5. Holophytic or saprophytic nutrition.
6. Oil is present as reserve material.
7. Contactile vacuole complex is present. Examples (i) Vacuolaria (ii) Coelomonas and (iii) Gomyostomum etc.
Order 6- Dinoflagellata: -
1. Amoeboid small planktonic flagellates provided either with a thick cuticle or cellulose covering or naked bodies.
2. Gullet (mouth) may be present or absent.
3. Chromatophores are variously coloured or may be absent.
4. Nutrition holophytic or holozoic.
5. Reserve material may be either starch or oil or both.
6. Complex system of vacuoles are provided.
7. Some species are emitting coloured light. (phosphorescent). Examples (i) Noctiluca and (ii) Ceratium
Sub-Class II- Zoomastigina: -
1. Chromatophores are absent.
2. Nutrition holozoic (animal-like), saprozoic or parasitic.
3. Usually more than two flagella are present.
4. Starch or other amyloid subtances as reserve material are always absent.
5. Conjugation (syngamy), never occurs.
Sub-class - Zoomastigina contains 4 orders: -
Order I - Rhizomastigina or Pantostomatida: -
1. Peculiar flagellates linking Sarcodina and Mastigophora.
2. Permanently amoeboid form.
3. Pseudopodia and flagella both are present. Examples : (i) Mastigina (ii) Mastigamoeba (iii) Actinomonas (iv) Mastigella and (v) Histomonas.
Order 2 - Protomonadina: -
1. Minute, simple flagellates with a thin cuticle, and naked amoeboidal body form.
2. Mouth (Gullet) absent.
3. Flagella 1 or 2 rarely more without supporting rods.
4. Holozoic nutrition in free living forms while in parasitic forms it is saprophytic. Examples (i) Choanoflagellates i.e. Proterospongia (ii) Trypanosoma (iii) Leishmania (iv) Monas and Oikomonas.
Order 3- Polymastigina: -
1. Minute, complex flagellates with delicate cuticle.
2. Mouth (Cytostome) present.
3. 3 to 8 or even more flagella are present.
4. 1 to several nuclei are present accompanied by a parabasal body and axostyle.
5. Mostly harmless internal parasites. Examples: (i) Trichonympha and (ii) Lophomonas,
Class 3. Sporozoa: -
1. Body covered with thick cuticle or pellicle.
2. The adult form is without external locomotary organs.
3. A single nucleus present, the meganucleus absent.
4. Due to adaptation of parasitic life mouth, vacuoles and anal opening are absent.
5. Nutrition by absorption through outer surface of the body.
6. A sexual reprodution by multiple fission and sexual reproduction by conjugation.
7. Life cycle complicated by alternation of sexual and asexual phases in different hosts.
8. Exclusively parasitic forms. Class sporozoa contains more than 2,000 species grouped in 3 sub-classes.
Sub-class 1 - Telosporidia: -
1. The adult trophozoite is uninucleate.
2. Some stages are intracellular.
3. Each simple spore is without polar capsule and filament contain one to many sporozoites.
4. life cycle completed with spore formation.
Order 1 - Gregarinida: -
1. Trophozoite or asexual adult is large, and extracellular, free and motile.
2. Zygote non-motile.
3. Sporozoites incased in capsules.
Sub-order 1 - Engregarinida: -
1. Life-cycle completed without schizogony. Examples : (i) Monocystis and (ii) Gregarina
Sub-order 2. Schizogregarinida
1. Schizogony and sporogony both occur in life cycle. Example : Schizocystis.
Order 2 - Coccidia: -
1. Trophozoite small and intracellular.
2. Zygote non motile.
3. Sporozoites in cased in capsules.
4. Parasites of Gut infecting epithelial cells. Examples: (i) Eimeria (ii) Coccidium and (iii) Isopora.
Order 3 - Haemosporidia: -
1. Mature trophozoite is amoeboid, small and intracellular.
2. Zygote motile.
3. Sporozoites are naked without capsules.
4. They are blood parasites of vertebrates. Examples: (i) Plasmodium and (ii) Babesia.
Sub-Class II - Cnidosporidia: -
1. Adult trophozoite is multinucleated.
2. Spore-formation occurs throughout life.
Order 1 - Myxosporidia: -
1. Spores large, with a bivalved membrane.
2. Trophozoite is not intracellular and amoeboid in shape. Examples : (1) Myxidium and (ii) Myxobolus.
Order 2- Actinomyxidia: -
1. Large spores with a trivalved membrane.
2. 3 Polar capsules, each with a filament. Examples (i) Triactinomyxon and (ii) Sphaeractinomyxon.
Order 3- Microsporidia: -
1. Small spores with a univalved membrane. Example : Nosema
Order 4 Helicosporidia: -
1. Spores small. Example : Helicosporidium
Sub-Class III - Acnidosporidia: -
1. Mature trophozoite having more than one nucleus.
2. Simple spores without polar capsules having a single sporozoite.
Order 1 - Sarcosporidia: -
1. Spore are naked without case.
2. Muscular parasites of higher vertebrates. Example: Sacrocystis
Order 2 Haplosporidia: -
1. Spores cases are present.
2. Parasited of fish and invertebrates. Examples : (i) Ichthyosporidium and (ii) Haplosporidium.
Class 1 - Ciliata of subphylum 2 - Ciliophora: -
About 2,500 species of this class are grouped in 2 subclasses which are further divided into orders.
Sub-Class I - Protociliata: -
1. Baby is uniformly covered by equal sized cilia.
2. Mouth (Cytostome) absent, food in liquid form absorbed by the entire outer body surface.
3. 2 to several nuclei, all of one type are present.
4. Contractile vacuoles are absent.
5. Reproduces asexualy by plasmotomy, Sexualy by syngamy or by complete fusion of gametes, No conjugation.
6. Encystment during unfavourable conditions.
7. They are intestinal parasites of amphibians.
Order 1 Opalinata: -
1. Character similar to sub-class Protociliata. Examples (i) Opalina (ii) Protoopalina and (iii) Cepedea
Sub-Class II- Euciliata: -
1. Cilia of unequal size are not uniformly distributed.
2. Mouth (Cytostome) is generally present.
3. Dimorphic i.e. both mega and micronuclei are preseat.
4. Contactile vacuoles are present.
5. Asexual reproduction by binary fission and sexual reproduction occurs by conjugation.
Order 1 Holoricha: -
1. Uniform cilia
Sub-order 1 Astomata: -
1. Cytostome absent. Example : Collinia
Sub-Order 2 Gymnostomata: -
1. Mouth present, opens at the time of feeding.
2. Simple gullet. Examples : (i) Prorodon (ii) Chilodon (iii) Dileptus (iv) Did inium and (v) Ichthyophthiritus
Sub-order 3 Hymenostomata: -
1. Mouth remain open permanently.
2. Complex gullet. Example : (i) Paramecium (ii) Frontonia (iii) Colpidium and (iv) Colpoda.
Order 2 - Spirotricha: -
1. Peristome upto general body surface.
2. Gullet with undulating membranes.
Sub-Order 1 Hetrotricha (Polytricha): -
1. Short cilia are uniformly distributed. Examples: (i) Balantidium (ii) Nyctotherus (iii) Stentor and (iv) pirostomum etc.
Sub-order 2 Oligotricha: -
1. Cilia absent are reduced to the adoral zone. Examples : (i) Diplodinum and (ii) Entodinium
Sub-Order 3 Hypotricha: -
1. Body flatterned.
2. Cilia, Cirri and membranellae present only on the ventral surface of the body. Examples : (i) Stylonchia (ii) Euplotes
Order 3 Chonotricha: -
1. Adoral zone of membranellae are clockwise bounded to mouth.
2. Spirally coiled peristome extending out like a funnel.
3. One type of Nucleus exists.
4. It is a permanent ectoparasite on the gills of Crustacea. Example: Spirochona
Order 4 Peritricha: -
1. Adoral zone of membranellae are anti-clockwise bounded to mouth.
2. Gullet bearing undulating membrane.
3. Cilia reduced to one or more.
4. Mostly sessile and colonial. Examples: (i) Vorticella (ii) Epistylis and (iii) Carchesium.
Class 2 Suctoria of Subphylum Ciliophora: -
1. Usually sessile Infusoria or highly specialized forms.
2. Young stages are motile due to presence of cilia.
3. Cilia is absent in adult sessile form which is provided with two types of tentacles serving as sucking and piercing organs.
4. Mouth and gullet absent.
5. Feeding upon other protozoans. Examples : (i) Podophrya (ii) Sphacrophrya (iii) Acineta (iv) Tokophrya (v) Ephelota and (vi) Dendrosoma.