What is Phylum Protozoa | Characters, Classification

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General Characters of Phylum Protozoa

1. Protozoa are microscopic animalcules With very simple organization.
2. These are unicellular having one is more nuclei.
3. The body may be naked or protected either with the pellicle or with the skeleton in the form of a test or cyst.
4. The single cell of the body performs All The  Vittal activities i.e., there is no physiological division of labor.
5. Animalcules may be free-living commensal or parasitic. The free-living forms are aquatic inhabiting fresh and salt waters. these may be solitary or Colonial. the parasitic form resides on or inside the body of animals and plants.
6. Nutrition may be holozoic (animal-like)  Holophytic  (Plant-like)  saprozoic ( subsisting on dead organic matter)  saprophytic ( feeding on liquid food) or parasitic.
7. The digestion is intracellular and is accomplished inside the food vacuole.
8. Locomotory organ may be pseudopodia or flagella or cilia or absent.
9. Respiration and excretion are brought about through the General Body surface. The contractile vacuole help in osmoregulation and excretion.
10. Asexual reproduction by binary fission, Multiple Fission, and budding.
11. Sexual reproduction by gamete formation or by the conjugation of adults.
12. Encystment occurs to tide over unfavorable conditions and to help in the dispersal of race.
13. In certain animalcules, the life cycle is complicated and exhibits alternation of generations.
14. About 50,000 known species.

So far we have known about the general characteristics of Phylum Protozoa, now we will know about its classification, so let us know about the classification.

Classification of phylum protozoa

The phylum Protozoa is divided into four subphyla.

1. Subphylum – Sarcomastigophora
2. Subphylum – Sporozoa
3. Subphylum – Cnidospora
4. Subphylum – Ciliophora

First of all, we know about the suborder Sarcomastigophora

Subphylum I – SARCOMASTIGOPHORA

• Locomotor organelles pseudopodia or flagella or both.
• Nucleus one or many and of the same kind.
• Asexual Reproduction by binary and Multiple Fission.

Superclass (A) Mastigophora (flagellata)

• Simple primitive and with a firm pellicle.
• Locomotor  organelles flagella.
• Nutrition is autotrophic or heterotrophic or both.

Class 1. Phytomastigophorea (Phytoflagellata)

• Chlorophyll-bearing Chromatophores are present.
• Nutrition is holophytic or phototrophic.
• Reserve food starch is paramylon.
• Flagella 1 or 2  or many.

ORDER 1 – Chrysomonadida

In this order or order of Phylum protozoa, we will study which type of organisms have been placed.

• Amoeboid forms without a gullet but with stigma.
• Flagella usually e one sometimes two or three.
• Chromatophores are one or two yellowish or brownish or yellowish-green.
• Starch is absent but leucosis and fats may be present.
• Siliceous cyst.
• Marine or freshwater animals.
• Examples – Chrysamoeba, Chromulina.

Order 2. Cryptomonadida

In this order of the phylum protozoa, we also know about what type of organisms have been placed.

• The anterior gullet reaches up to the middle of the body.
• Flagella 2 and unequal.
• Chromatophores 2 Brown yellow or colorless.
• Reserve food starch.
• Stigma present.
• Marine or freshwater.

Example – Chilomonas, Cryptomonas etc.

ORDER 3. Euglenoida

What types of animals have been placed in this order or group of Phylum protozoa, you will know about them.

• Anterior end with a  gullet or Cytopharynx leading into a reservoir.
• Flagella one or two to and with mastigonemes.
• Chromatophores are numerous and green.
• Reserve food stuff paramylon and oil.
• Stigma present.
• Mostly freshwater.

Example – Euglena, Peranema, Rhabdomanas.

ORDER 4. Volvocida (=Phytomonadida)

In this fourth order of the phylum protozoa, we also know about what types of animals have been placed.

• Small with rigid cellulose covering and gullet.
• Flagella usually to sometimes more.
• Chromatophores are green and numerous.
• Reserve food stuff starch and oils.
• Stigma present.
• Mostly freshwater some from Colonies.

Examples – Chlamydomonas, Volvox.

ORDER 5. Chloromonadida

In this fifth order of the Phylum protozoa, which type of animals have been kept, you will know about them.

• Dorso-ventrally forms with a delicate pellicle.
• Gullet present.
• Flagella 2 sometimes 1 or more.
• Chromatophores are green and numerous, some colorless.
• Reserve food stuff oil.
• No stigma.
• Largely freshwater.

Example – Coelomonas

ORDER 6. Dinoflagellida

In this sixth order of the phylum protozoa, we also study what types of organisms have been placed.

• Small and planktonic, naked and amoeboid, or with a thick pellicle or theca.
• Flagella 2.
• Chromatophores numerous yellow to Brown.
• Reserve food starch or oil or both.
• Stigma present  contractile vacuoles  2.
• Some are  bioluminescent.
• Largely married some parasitic.

Examples – Noctiluca, Ceratium, and Gymnodinium.

Class 2. Zoomastigophorea (=Zooflagellata)

We know about what types of animals have been kept in this class or the class of Phylum Protozoa.

• Chlorophyll-bearing chromatophores are absent.
• Nutrition and holozoic  or saprozoic.
• Parasitic symbiotic or free living.
• Reserve food glycogen.
• Flagella one too many.

ORDER 1. Rhizomastigida

• Small and amoeboid.
• Flagella  1 to 4.
• Locomotion by   flagella or pseudopodia.
• Chiefly freshwater.

Examples – Mastigamoeba, Dimorpha.

ORDER 2. Kinetoplastida

• Small and more or less amoeboid in form.
• Flagella 1 or 2.
• Holozoic or saprozoic  nutrition.
• Solitary or colonial.
• Parasitic forms live in blood.

Examples – Leishmania, Trypanosoma, Bodo.

ORDER 3. Choanoflagellida

•  Free-living.
•  Colonial.
•  A collar around the base of a single flagellum.
•  Nutrition holozoic.

Example – Proterospongia.

ORDER 4. Diplomonadida

• Small with a delicate Pellicle and a cytostome.
• Flagella 3 to 8 form the border of the undulating membrane.
• Uninucleate sometimes multinucleate.
• Mostly intestinal parasites.

Example – Giardia, Hexamita.

ORDER 5. Hypermastigida

• Highly Specialised phone with numerous flagella.
• Kinetostomes or parabasal bodies are arranged in a circle or Longitudinal or spiral row.
• Uninucleate or Multinucleate.
• Mouth absent, food ingested by pseudopodia.
• Gut parasites of termites and cockroaches.

Example – Triychonympha, Lophomonas.

ORDER 6. Trichomanadida

• Flagella 4-6.
• One flagellum trailing.
• Parasites in genital passage.

Example – Trichomonas

Superclass (B). Opalinata

• The body is covered by flagella or cilia.
• Nuclei 2 are too many and monomorphic.
• Nutrition saprozoic.
• Reproduction by binary fission or by gametes.
• Parasites of frogs and toads.

Example – Opalina.

Superclass (C) Sarcodina (=Rhizopoda)

• The body is without a definite pellicle.
• Locomotion by Pseudopodia.
• Nutrition holozoic or saprozoic.
• Asexual reproduction by Binary fission.
• Solitary and free-living, some parasitic or colonial.

Class 1. Actinopodea

Pseudopodia are axopodia with axial filaments radiating from the spherical body.

Subclass (1) Heliozoa

• Spherical protozoans.
• Pseudopodia (axopodia) radiating.
• The body is naked and differentiated into outer vacuolated ectoplasm and inner dense endoplasm.
• Nutrition holozoic.
• Mostly freshwater.

Example – Actinophrys, Clathrulina Actinosphaerium.

Subclass (2) Radiolaria

• Perforated central capsule separating the ectoplasm from endoplasm.
• Contractile vacuole absent.
• Pseudopodia are axopodia or filopodia.
• Skeleton of siliceous spicules.
• Marine.

Example – Collozoum.

Subclass (3) Proteomyxidia

• Pseudopodia are filopodia.
• Marine or freshwater.
• Reproduction by binary or multiple fission.

Example –Pseudospora

Subclass (4) Acantharia

• Central capsule non-chitinoid and without pores.
• Skeleton of strontium sulphate.
• Pseudopodia are axopodia.

Example – Acanthrometra

 Class 2. Rhizopodea

• Pseudopodia are lobopodia, filopodia or reticulopodia without axial filaments.

Subclass (1) Lobosia

Pseudopodia are Labopodia.

ORDER 1. Amoebida

• Bosy amoeboid, without a skeleton.
• Pseudopodia (lobopodia) short with blut ends.
• Ectoplasm and endoplasm distinct.
• Largely fresh water, some parasites.

Example – Amoeba, Entamoeba  

ORDER 2. Arcellinida (=Testacida)

• Body enclosed in one-chambered shell.
• Shell with a single opening through which lobopodia protrude.
• Free-living, found in freshwater.

Examples – Arcella, Difflugia, Euglypha.

Subclass (2) Filosia

• Pseudopodia are filopodia, tapering and branching.
• Body naked or with shell wth single aperture.
• Ectoplasm not distinct.
• Marine and freshwater forms.

Examples – Allogromia, Penardia.

Subclass (3) Granuloreticulosia

Pseudopodia and reticulopodia.

ORDER Foraminiferida

• Large-sized with uni-or multi-chambered shell.
• Shell with one or more openings through which reticulopodia emerge.
• Reticulopodia fine and branching forming a network.
• Mainly marine.

Example – Globigerina, Elphidium (=Polystomella)

Subclass (4) Mycetozoia

• Body large, amoeboid and multinucleate.
• Pseudopodia numerous and blunt.
• Form sporangia with spores.

Example – Slime molds.

Class 3. Piroplasmea

• Small parasites in R.B.Cs of vertebrates.
• Do not form spores.

Example – Babesia

• Now we will know entirely about the second suborder Sporozoa of the Phylum Protozoa.

Subphylum II. SPOROZOA

• Exclusively endoparasites.
• Body with a thick pellicle.
• Locomotor organelles absent in adult.
• Nutrition saprozoic.
• Asexual reproduction by multiple fission and sexual reproduction by syngamy followed by spore formation.
• Life-cycle includes both asexual and sexual phases.

Class 1. Telosporea

• Spore without polar capsule or filaments.
• Sporozoites elongated, and microgametes flagellated.
• Trophozoites with one nucleus only.

Subclass (1) Gregarinia

• Trophozoites large and found in the gut and body cavities (i.e. extracellular) of invertebrates.
• Gametocytes show syzygy.
• Zygote non-motile.
• Male and female gametes merogamous.
• Sporozoites found in sporocysts.
• Parasites of invertebrates.

Examples – Monocystis, Gregarinia, Nematocystis.

Subclass (2) Coccidia

• Trophozoites are small and intracellular.
• Gametocytes are dimorphic.
• Sporozoites in sporocysts (oocysts).
• Blood or gut parasites of vertebrates.

Example – Eimeria, Isospora Plasmodium.

Class 2. Toxoplasmea

• Spores not formed.
• Only asexual reproduction.

Example – Toxoplasmea

Class 3. Haplosporea

• Spores with spore cases.
• Parasites of fish and invertebrates.
• Pseudopodia may be present but no flagella.
• Reproduction by schizogony only (asexual).

Examples – Ichthyosporidium, Haplosporidium.

Now we will study completely step by step the third suborder of Phylum Protozoa.

Subphylum III. CNIDOSPORA

• Trophozoites have many nuclei.
• Spore formation occurs throughout life.
• Spores contain polar capsules with polar filaments.

Class 1. Myxosporidea

• Spores develop from several nuclei.
• Spores within two or three valves.
• Trophozoites are amoeboid.

Example – Myxidium

ORDER 2. Actinomyxida

• Spores are large and with a trivalve membrane.
• Polar capsules 3, each with a filament.

Example – Triactinomyxon, Sphaeractinomyxon.

class 2. Microsporidia

• Spores are small and with a univalved membrane.
• With or without a polar capsule.

Example – Nosema

Subphylum IV. CILIOPHORA

• Body organization complex.
• Presence of cilia as feeding and locomotory organelles at some stage in the life cycle.
• Two types of nuclei -micronucleus and macronucleus are present.
• Asexual reproduction by binary fission or budding.
• Sexual reproduction by conjugation.

Class 1. Ciliata (Infusoria)

• Protozoa with a definite form and size.
• The body is bounded externally by a firm pellicle.
• Locomotor organelles cilia.
• Definite mouth (cytoplasm) and gullet present. Anal aperture (cytopyge) permanent.
• One or more contractile vacuoles present.
• Have two kinds of nuclei-large macronucleus and smaller micronucleus.

Subclass (1) Holotrichia

• Body cilia uniform.
• Buccal cilia are absent.

ORDER 1. Gymnostomatida

• Body large.
• Buccal cilia are absent.
• Cytostome opens to outside.

Examples – Coleps, Didinium, Nassula.

ORDER 2. Trichostomatida

• Cytostome at the bottom of vestibule.
• Spiral rows of cilia in vestibule; no cilia in buccal region.

Example – Colpoda, Balantidium.

ORDER 3. Chonotrichida

• Body vase-shaped.
• Body cilia absent.
• Funnel at the free end of the body with vestibular cilia.
• Ectocommensal on crustaceans.

Example – Lobochona, Spirochona.

ORDER 4. Apostomatida

• Body with spirally arranged Cilia.
• Cytostome mid-ventral.
• Parasites are commensals with a Complex life cycle completed on two hosts.

Example – Hyalophysa, Polyspira.

ORDER 5. Astomatida

• Cytostome absent.
• Body ciliation uniform.
• Parasites or commensals in the gut and coelom of earthworms.

Example – Anoplohyra, Hoplitophyra.

ORDER 6. Hymenostomatida

• The body is small and with uniform cilia on the body.
• Buccal cavity with undulating membrane and adoral zone of membranes cells.

Examples – Copidium, paramecium, Tetrahymena.

ORDER 6. Hymenostomatida

• Organisms of this group have similar cilia on their body along with being small.
• The membrane is the synovial region of cells and the oral cavity with a wavy membrane.

Examples – Copidium, paramecium, Tetrahymena.

Subclass (2) Peritrichia

• Adult without body cilia.
• Apical end with buccal cilia.
• Sessile organism

ORDER 1. Peritrichida

• The character of subclass peritricha.

Examples – Vorticella, Carchesium.

Subclass (3) Suctoria

• Body sessile and stalked.
• Young with Celia adult with tentacles.

ORDER 1. Suctorida

• Character as of subclass suctoria.

Example – Ephelota, Podophrya.

Subclass (4) Spirotricha

• Body cilia reduced.
• Buccal cilia well marked.

ORDER 1. Heterotrichida

• Body encased in lorica.
• Body cilia are usually absent.
• Body naked with uniform body cilia.

Examples – Bursaria, Stentor, and Blepharisma.

ORDER 2. Hypotrichida

• Body dorso-ventrally flattened.
• Body cilia at ventral side, forming cirri.

Example– Euplotes, Kerona.

ORDER 3. Oligotrichida

• Body cilia reduced or absent. 
• Buccal membranelles at front end only.

Examples – Strombidium, Halteria.

Conclusion –

Friends, we have learned about the Phylum Protozoa, and its subphylum, superclass, class, order, and characteristics.

So, friend, I hope that you have liked the given information about phylum protozoa. If you liked this article then share it with your friends.

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