Protozoans: Classification | Zoology Optional Notes for UPSC PDF Download

Sub-Phylum—Sarcomastigophora

• Locomation by flagella or pseudopodia or both.
• Nucleus one or more and monomorphic.
• Nutrition autotrophic or heterotrophic or both.
• Reproduction asexual and sexual by syngamy. Life cycle may show alternation of generation.

Super-Class—Mastigophora

• Flagellates with flagella for locomotion and covered with pellicle.
• Nutrition, autotrophic or heterotrophic or both.
• Longitudinal binary fission.
• 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.

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

• Usually possess chromatophores and so nutrition mostly holophytic by phototrophy. Stored food is paramylum.
• These possess only one or two flagella.
• Life cycle, asexual and sexual too in some cases.

Order-1. Chloromonadida

• Small covered with delicate flattened pellicle.
• Numerous green and some colourless chromatophores, Gullet present. Nutrition is usually by phototrophy. Reserve food is oil.
• Usually two flagella, sometimes more or even one.
• No stigma, complex contractile vacuole.
• Mostly fresh water forms.
  Examples: Vacularia, Coelomonas etc.

Order-2. Englenoidida

• Large with thick and firm pellicle. 
• 1 or 2 flagella. Gullet and cytopharynx leading into reservoir. 
• Chromatophores, green, and many, sometimes colourless. Nutrition is mostly by phototrophy. Reserve food is paramylum and oils. 
• Stigma and contractile vacuole present. 
• Mostly fresh water.
  Examples: Euglena, Peranema, etc.

Order—3. Volvocida (Phytomonadina)

• Small with thick cellulose theca. No gullet. 
• 2 or more flagella. 
• Numerous green and colourless chromatophores. Nutrition is mostly by phototrophy. Reserve food is starch. 
• Stigma present. 
• Sexual reproduction by syngamy. 
• Mostly fresh water, some colonial.
  Examples: Volvox, Chlamydomones etc.

Order—4. Cryptomonadida

• Small with rigid pellicle. Gullet up to the middle of body. 
• With two flagella, stigma present. 
• Green, yellow, brown or colourless chromatophores. 
• Nutrition usually by phototrophy. Reserve food is starch, sometimes oil. 
• Marine or fresh water.
  Examples: Chilomonas, Cryptomonas, etc.

Order—5. Chrysomonadina

• Small, having amoeboid movement, covered with a thin pellicle. 
• One to three flagella. 
• Yellow or brown chromatophores and nutrition, by phototrophy. 
• Siliceous cysts are formed.
• Marine or fresh water.
  Examples: Chromulina, Symura, Chrysamoeba, etc.

Order—6. Dinoflagellida

• Small, naked and amoeboid or have thick pellicle or cellulose theca. 
• Two flagella in the grooves. 
• Numerous yellow to brown chromatophores, Gullet present. Nutrition, mostly by phototrophy. Reserve food is starch and oil. 
• Stigma present. Two contractile vacuoles. 
• Some show bioluminescence.
• Mostly marine, some parasitic.
  Examples: Noctiluca, Ceratium etc.

Class—II. Zoomastigopohrea

• Chlorophyll or chromatophores absent. Mostly parasitic.
• Nutrition holozoic or saprozoic.
• Reserve food glycogen.
• Flagella one to many.

Order—1. Choanoflagellida

• A collar round the base of a single flagellum. 
• Free-living, solitary or colonial.
  Example: Proterospongia.

Order—2. Diplomonadida: 

• Bilaterally symmetrical, binucleate, with delicate pellicle and often with a cytostome. 
• Flagella 3 to 8. One often trailing or forming border of an undulating membrane. 
• Mostly intestinal parasites.
  Examples: Hexamita, Giardia.

Order—3. Hypermastigida: 

• Highly specialized, numerous flagella. 
• Kinetosomes arranged in a circle, plate or longitudinal or spiral rows. 
• Mouth absent. Food ingested by pseudopodia. 
• Gut parasites of termites and cockroaches.
  Examples: Lophomonas, Trychonympha.

Order—4. Rhizomastigida: 

• Small, amoeboid, chiefly freshwater. 
• Locomotion by 1-4 flagella and pseudopodia.
  Examples: Mastigamoeba, Dimorpha.

Order—5. Kinetoplastida: 

• No gullet. Kinetoplast present. 
• Flagella 1 to 4. No definite pellicle. 
• Mostly parasitic forms living in blood.
  Examples: Bodo, Leishmania, Trypanosoma.

Order—6. Trichomonadida: 

• Flagella 4 to 6. One flagellum trailing. 
• Parasites of vertebrates.
  Example: Trichomonas.

Super-Class—Opalinata 

• Body covered by cilia like organelles in oblique rows. 
• Numerous monomorphic nuclei. 
• Interkinetal binary fission. Sexual reproduction by snygamy with flagellated anisogametes. 
• Parasitic in frogs and toads.
  Example: Opalina.

Super-Class—Sarcodina (Rhizopoda) 

• No definite pellicle, some have exoskeleton.
• Adult move by pseudopodia. 
• Nutrition, holozoic or saprozoic. 
• Asexual reproduction by binary fission, sexual by gametes and may form flagellated young. No spore formation. 
• 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 

• Body amoeboid, naked, without skeleton. 
• Nucleus with honeycomb lattice. 
• Largely freshwater and free-living. Many parasitic.
  Examples: Amoeba, Entamoeba, Pelomyxa.

Order—2. Arcellinida (= Testacida)

• Body enclosed in one-chambered shell of pseudochitin, with a single opening through which lobopodia protrude.
• Free-living, mostly freshwater. 
  Examples: Arcella, Difflugia, Euglypha.

Sub-Class—4. Mycetozoia:

• Large, amoeboid and multinucleate. 
• Exoskeleton or central capsule present. 
• Numerous, blunt pseudopodia. 
• Nutrition is phagocytic. 
• Sexual reproduction forming sporangia.
  Example: Didynium.

Class—IV. Actinopodea

Pseudopodia as axopodia with axial filaments, radiating from spherical body.

Sub-Class—1. Helizoia: 

• Rounded body called sun-animalcules covered with radiating axopodia. Usually with more than one nucleus. 
• Mostly naked, some with siliceous scales or spines. 
• Nutrition holozoic. 
• Mostly fresh water.
  Examples: Actinophrys, Actinosphaerium etc.

Sub-Class—2. Proteomyxidia

• Pseudopodia are filopodia. 
• Reproduction by binary or multiple fissions usually within the cyst. 
• Marine or fresh water, usually parasite on algae.
  Example: Pseudospora.

Sub-Class—3. Radiolaria

• Preforated central capsule in between ectoplasm and endoplasm. 
• Skeleton of siliceous spicules. Filopodia or axopodia is present. 
• All marine.
  Examples: Collozoum; Lithocircus.

Sub-Class—1. Acantharia

• Imperforate non-chitinoid central capsule without pores. 
• Skeleton of strontium sulphate. 
• Pseudopodia are axopodia.
  Example: Acanthometra.

Class—V. Piroplasmea

Small round, rod-shaped or amoeboid parasites in the vertebrate red blood corpuscles.
Example: Babesia.

Sub-Phylum—Sporozoa:

• Body with thick pellicle.
• No locomotor organs in adult. Cilia or flagella may be present in gametes.
• Nutrition is saprozoic.
• Asexual reproduction by multiple fission and sexual reproduction by syngamy followed by spore formation.
• All endoparasites.

Class—1. Telosporea

• Locomotion by gliding or body flexion.
• Spore formation.
• Both a sexual and sexual reproduction with flagellated microgametes in some.

Sub-Class—1. Gregarinia: 

• Mature trophozoites large, extracellular in host’s gut and body activities. 
• Each spore produces 8 sporozoites. 
• Parasites in invertebrates.
  Examples: Monocystis, Gregarina.

Sub-Class—2. Coccidia: 

• Mature trophozoites small and intracellular. 
• Gametocytes are dimorphic. 
• 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: 

• Spores are absent.
• Reproduction by binary fission, cysts is formed.

Sub-Phylum—Cnidospora

• Adult trophozoite with many nuclei. 
• Spore formation. 
• Zygote forms one or more trophozoite without sporogony.

Class—1. Myxosporidea: 

• Spores large, developed from several nuclei. 
• Spores with two or three valves. 
• Parasites mostly in fishes.
  Examples: Myxidium, Myxobolus, Ceratomyxa.

Class—2. Microsporidea: 

• Spores small, developed from one nucleus. 
• Spores with a univalved membrane. 
• Intracellular parasites in arthropods and fishes.
  Example: Nosema.

Sub-Phylum—Ciliophora

Class—1. Ciliata: 

• Cilia or compound ciliary organelles for locomotion.
• Usually two types of nuclei, macro and micro. 
• Asexual reproduction by binary fission and sexually by conjugation.

Sub-Class—1. Peritrichia

• No cilia on the body of the adult. Mostly sessile.
• Apical end with buccal cilia.

Order—1. Pertrichida:

• Adults without cilia but buccal ciliature present.
• Mostly attached stalked animals.
  e.g. Vorticella, Carchesium.

Sub-Class—2. Suctoria:

• Sessile and stalked body.
• Young with cilia, adult with suctorial tentacles.

Order—2. Suctorida

• Sessile, stalked with distal end bearing tentacles.
• No cilia in adult.
  Example: Ephenota.

Sub-Class—3. Heterotrichida

Body with uniform cilia or encased in a lorica.
Examples: Nyctotherus, Bursaria, etc.

Order—1. Oligotrichida: 

• Small ciliates with reduced cilia or cilia absent. 
• 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

• Simple and uniform cilia on body. 
• 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:

• Small ciliates with uniform body ciliation. 
• Buccal cavity with undulating membrane.
  Example: Colpidium, Paramecium.

Order—3. Trichostomatida

• Spiral row of cilia in vestibule. 
• Cytostome opens at the bottom of vestibule. Example: Colpidium, Paramecium.

Order—4. Astomatida: 

• Cytostome absent with uniform body ciliation. 
• Commensals or endoparasites in the gut and coelom of oligochaete worms.
  Example: Anoplophyra.

Order—5. Apostomatide: 

• Body has spirally arranged cilia.
• Cytostome is mid-ventral. 
• Life cycle complex with two hosts, one of them is crustacean. 
• Marine and parasitic or commensals.
  Example: Hyalophsya.

Order—6. Chonatrichida: 

• Vase-shaped body without body cilia. 
• A funnel at the free end bears vestibular cilia. 
• Mostly marine and ectocommensal on crustaceans.
  Example: Spirochona.