In this article we will discuss about various classification of protozoans.
Sub-Phylum—Sarcomastigophora:
(i) Locomation by flagella or pseudopodia or both.
(ii) Nucleus one or more and monomorphic.
(iii) Nutrition autotrophic or heterotrophic or both.
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(iv) Reproduction asexual and sexual by syngamy. Life cycle may show alternation of generation.
Super-Class—Mastigophora:
(i) Flagellates with flagella for locomotion and covered with pellicle.
(ii) Nutrition, autotrophic or heterotrophic or both.
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(iii) Longitudinal binary fission.
(iv) May be free swimming or parasitic.
Caerulin:
Caerulin is a decapeptide produced by the skin of the frog Hyla caerulea. Its structure and functions resemble both gastrin and cholecystokinin-pancreozymin. It has strong stimulatory effect on the contractions of gall bladder.
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Gastrone:
Gastric mucosa has a substance known as gastrone. It inhibits the secretion of gastric acid stimulated by histamine and gastrin.
Villikinin:
This hormone is secreted by the upper ileum stimulated by the entry of acid chyme. This hormone stimulates the movement of intestinal villi.
A summary of the sources, site of action and effects produced is given below:
Class—I. Phytomastigophora:
(i) Usually possess chromatophores and so nutrition mostly holophytic by phototrophy. Stored food is paramylum.
(ii) These possess only one or two flagella.
(iii) Life cycle, asexual and sexual too in some cases.
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Order—1. Chloromonadida:
(i) Small covered with delicate flattened pellicle.
(ii) Numerous green and some colourless chromatophores, Gullet present. Nutrition is usually by phototrophy. Reserve food is oil.
(iii) Usually two flagella, sometimes more or even one.
(iv) No stigma, complex contractile vacuole.
(v) Mostly fresh water forms.
Examples:
Vacularia, Coelomonas etc.
Order—2. Englenoidida:
(i) Large with thick and firm pellicle.
(ii) 1 or 2 flagella. Gullet and cytopharynx leading into reservoir.
(iii) Chromatophores, green, and many, sometimes colourless. Nutrition is mostly by phototrophy. Reserve food is paramylum and oils.
(iv) Stigma and contractile vacuole present.
(v) Mostly fresh water.
Examples:
Euglena, Peranema, etc.
Order—3. Volvocida (Phytomonadina):
(i) Small with thick cellulose theca. No gullet.
(ii) 2 or more flagella.
(iii) Numerous green and colourless chromatophores. Nutrition is mostly by phototrophy. Reserve food is starch.
(iv) Stigma present.
(v) Sexual reproduction by syngamy.
(vi) Mostly fresh water, some colonial.
Examples:
Volvox, Chlamydomones etc.
Order—4. Cryptomonadida:
(i) Small with rigid pellicle. Gullet up to the middle of body.
(ii) With two flagella, stigma present.
(iii) Green, yellow, brown or colourless chromatophores.
(iv) Nutrition usually by phototrophy. Reserve food is starch, sometimes oil.
(v) Marine or fresh water.
Examples:
Chilomonas, Cryptomonas, etc.
Order—5. Chrysomonadina:
(i) Small, having amoeboid movement, covered with a thin pellicle.
(ii) One to three flagella.
(iii) Yellow or brown chromatophores and nutrition, by phototrophy.
(iv) Siliceous cysts are formed.
(v) Marine or fresh water.
Examples:
Chromulina, Symura, Chrysamoeba, etc.
Order—6. Dinoflagellida:
(i) Small, naked and amoeboid or have thick pellicle or cellulose theca.
(ii) Two flagella in the grooves.
(iii) Numerous yellow to brown chromatophores, Gullet present. Nutrition, mostly by phototrophy. Reserve food is starch and oil.
(iv) Stigma present. Two contractile vacuoles.
(v) Some show bioluminescence.
(vi) Mostly marine, some parasitic.
Examples:
Noctiluca, Ceratium etc.
Class—II. Zoomastigopohrea:
(i) Chlorophyll or chromatophores absent. Mostly parasitic.
(ii) Nutrition holozoic or saprozoic.
(iii) Reserve food glycogen.
(iv) Flagella one to many.
Order—1. Choanoflagellida:
(i) A collar round the base of a single flagellum.
(ii) Free-living, solitary or colonial.
Example:
Proterospongia.
Order—2. Diplomonadida:
(i) Bilaterally symmetrical, binucleate, with delicate pellicle and often with a cytostome.
(ii) Flagella 3 to 8. One often trailing or forming border of an undulating membrane.
(iii) Mostly intestinal parasites.
Examples:
Hexamita, Giardia.
Order—3. Hypermastigida:
(i) Highly specialized, numerous flagella.
(ii) Kinetosomes arranged in a circle, plate or longitudinal or spiral rows.
(iii) Mouth absent. Food ingested by pseudopodia.
(iv) Gut parasites of termites and cockroaches.
Examples:
Lophomonas, Trychonympha.
Order—4. Rhizomastigida:
(i) Small, amoeboid, chiefly freshwater.
(ii) Locomotion by 1-4 flagella and pseudopodia.
Examples:
Mastigamoeba, Dimorpha.
Order—5. Kinetoplastida:
(i) No gullet. Kinetoplast present.
(ii) Flagella 1 to 4. No definite pellicle.
(iii) Mostly parasitic forms living in blood.
Examples:
Bodo, Leishmania, Trypanosoma.
Order—6. Trichomonadida:
(i) Flagella 4 to 6. One flagellum trailing.
(ii) Parasites of vertebrates.
Example:
Trichomonas.
Super-Class—Opalinata:
(i) Body covered by cilia like organelles in oblique rows.
(ii) Numerous monomorphic nuclei.
(iii) Interkinetal binary fission. Sexual reproduction by snygamy with flagellated anisogametes.
(iv) Parasitic in frogs and toads.
Example:
Opalina.
Super-Class—Sarcodina (Rhizopoda):
(i) No definite pellicle, some have exoskeleton.
(ii) Adult move by pseudopodia.
(iii) Nutrition, holozoic or saprozoic.
(iv) Asexual reproduction by binary fission, sexual by gametes and may form flagellated young. No spore formation.
(v) Fresh water, marine or in moist soil, a few parasitic.
Class—III. Rhizopodea:
Pseudopodia as lobopodia, filopodia or reticulopodia, without axial filaments.
Sub-Class—1. Filosia:
Pseudopodia as filopodia. Naked or with a shell with single aperture.
Examples:
Allogromia, Penardia (naked).
Sub-Class—2. Granuloreticulosia:
Pseudopodia delicate granular reticulopodia.
Order-1. Foraminiferida:
Large sized with uni-or multi-chambered calcareous shell with one or more openings through which reticulopodia emerge.
Examples:
Globigerina, Elphidium (= Polystomella)
Sub-Class—3. Lobosia:
Pseudopodia as lobopodia.
Order—1. Amoebida:
(i) Body amoeboid, naked, without skeleton.
(ii) Nucleus with honeycomb lattice.
(iii) Largely freshwater and free-living. Many parasitic.
Examples:
Amoeba, Entamoeba, Pelomyxa.
Order—2. Arcellinida (= Testacida):
(i) Body enclosed in one-chambered shell of pseudochitin, with a single opening through which lobopodia protrude.
(ii) Free-living, mostly freshwater.
Examples:
Arcella, Difflugia, Euglypha.
Sub-Class—4. Mycetozoia:
(i) Large, amoeboid and multinucleate.
(ii) Exoskeleton or central capsule present.
(iii) Numerous, blunt pseudopodia.
(iv) Nutrition is phagocytic.
(v) Sexual reproduction forming sporangia.
Example:
Didynium.
Class—IV. Actinopodea:
Pseudopodia as axopodia with axial filaments, radiating from spherical body.
Sub-Class—1. Helizoia:
(i) Rounded body called sun-animalcules covered with radiating axopodia. Usually with more than one nucleus.
(ii) Mostly naked, some with siliceous scales or spines.
(iii) Nutrition holozoic.
(iv) Mostly fresh water.
Examples:
Actinophrys, Actinosphaerium etc.
Sub-Class—2. Proteomyxidia:
(i) Pseudopodia are filopodia.
(ii) Reproduction by binary or multiple fissions usually within the cyst.
(iii) Marine or fresh water, usually parasite on algae.
Example:
Pseudospora.
Sub-Class—3. Radiolaria:
(i) Preforated central capsule in between ectoplasm and endoplasm.
(ii) Skeleton of siliceous spicules. Filopodia or axopodia is present.
(iii) All marine.
Examples:
Collozoum; Lithocircus.
Sub-Class—1. Acantharia:
(i) Imperforate non-chitinoid central capsule without pores.
(ii) Skeleton of strontium sulphate.
(iii) Pseudopodia are axopodia.
Example:
Acanthometra.
Class—V. Piroplasmea:
1. Small round, rod-shaped or amoeboid parasites in the vertebrate red blood corpuscles.
Example:
Babesia.
Sub-Phylum—Sporozoa:
(i) Body with thick pellicle.
(ii) No locomotor organs in adult. Cilia or flagella may be present in gametes.
(iii) Nutrition is saprozoic.
(iv) Asexual reproduction by multiple fission and sexual reproduction by syngamy followed by spore formation.
(v) All endoparasites.
Class—1. Telosporea:
(i) Locomotion by gliding or body flexion.
(ii) Spore formation.
(iii) Both a sexual and sexual reproduction with flagellated microgametes in some.
Sub-Class—1. Gregarinia:
(i) Mature trophozoites large, extracellular in host’s gut and body activities.
(ii) Each spore produces 8 sporozoites.
(iii) Parasites in invertebrates.
Examples:
Monocystis, Gregarina.
Sub-Class—2. Coccidia:
(i) Mature trophozoites small and intracellular.
(ii) Gametocytes are dimorphic.
(iii) Parasite in the blood or gut of vertebrates.
Examples:
Eimeria, Plasmodium, etc.
Class—2. Haplosporea:
Spore cases present. Only asexual reproduction.
Example:
Ichthyosporidium.
Class—3. Toxoplasmea:
(i) Spores are absent.
(ii) Reproduction by binary fission, cysts is formed.
Sub-Phylum—Cnidospora:
(i) Adult trophozoite with many nuclei.
(ii) Spore formation.
(iii) Zygote forms one or more trophozoite without sporogony.
Class—1. Myxosporidea:
1. Spores large, developed from several nuclei.
2. Spores with two or three valves.
3. Parasites mostly in fishes.
Examples:
Myxidium, Myxobolus, Ceratomyxa.
Class—2. Microsporidea:
(i) Spores small, developed from one nucleus.
(ii) Spores with a univalved membrane.
(iii) Intracellular parasites in arthropods and fishes.
Example:
Nosema.
Sub-Phylum—Ciliophora:
Class—1. Ciliata:
(i) Cilia or compound ciliary organelles for locomotion.
(ii) Usually two types of nuclei, macro and micro.
(iii) Asexual reproduction by binary fission and sexually by conjugation.
Sub-Class—1. Peritrichia:
(i) No cilia on the body of the adult. Mostly sessile.
(ii) Apical end with buccal cilia.
Order—1. Pertrichida:
(i) Adults without cilia but buccal ciliature present.
(ii) Mostly attached stalked animals.
e.g. Vorticella, Carchesium.
Sub-Class—2. Suctoria:
(i) Sessile and stalked body.
(ii) Young with cilia, adult with suctorial tentacles.
Order—2. Suctorida:
(i) Sessile, stalked with distal end bearing tentacles.
(ii) No cilia in adult.
Example:
Ephenota.
Sub-Class—3. Heterotrichida:
1. Body with uniform cilia or encased in a lorica.
Examples:
Nyctotherus, Bursaria, etc.
Order—1. Oligotrichida:
(i) Small ciliates with reduced cilia or cilia absent.
(ii) Buccal membranelles extend around apical end of body.
Example:
Halteria.
Order—2. Hypotrichida:
Dorso-ventrally flattened. Fused cilia forming ventral cirri.
Examples:
Euplotes, Stylonchia.
Sub-Class—4. Holotricha:
(i) Simple and uniform cilia on body.
(ii) Buccal cilia either absent or rudimentary.
Order—1. Gymnostomatida:
Large ciliates without oral ciliature. Cytostome opens directly. No vestibule.
Examples:
Coleps, Didinium, Prorodon, Dileptus.
Order—2. Hymenostomadia:
(i) Small ciliates with uniform body ciliation.
(ii) Buccal cavity with undulating membrane.
Example:
Colpidium, Paramecium.
Order—3. Trichostomatida:
(i) Spiral row of cilia in vestibule.
(ii) Cytostome opens at the bottom of vestibule.
Example:
Colpidium, Paramecium.
Order—4. Astomatida:
(i) Cytostome absent with uniform body ciliation.
(ii) Commensals or endoparasites in the gut and coelom of oligochaete worms.
Example:
Anoplophyra.
Order—5. Apostomatide:
(i) Body has spirally arranged cilia.
(ii) Cytostome is mid-ventral.
(iii) Life cycle complex with two hosts, one of them is crustacean.
(iv) Marine and parasitic or commensals.
Example:
Hyalophsya.
Order—6. Chonatrichida:
(i) Vase-shaped body without body cilia.
(ii) A funnel at the free end bears vestibular cilia.
(iii) Mostly marine and ectocommensal on crustaceans.
Example:
Spirochona.