Protozoa: The Microscopic World

Protozoa: The Microscopic World

• Definition: Unicellular organisms lacking tissues and organs. Perform all life functions within a single cell.
• Characteristics:
  • Microscopic, requiring a microscope for observation.
  • Simplest and most primitive animals, demonstrating protoplasmic organization.
  • Single cell with one or more nuclei, but no nucleus specializes in a particular function.
  • Exist solitary or in colonies where individuals remain independent.
  • Exhibit diverse body symmetries, including radial, bilateral, and spherical.
  • Locomotion through finger-like pseudopodia, whip-like flagella, or hair-like cilia. Some may lack locomotion.
  • Nutrition varies — holozoic (animal-like), holophytic (plant-like), saprozoic, or parasitic. Digestion occurs within food vacuoles.
  • Respiration and excretion through the cell surface or contractile vacuoles, primarily regulating osmotic balance .
  • Reproduction via binary fission, multiple fission, budding, or sexual processes involving conjugation or fusion of gametes.
  • Cryptomonadida: Rigid pellicle, anterior gullet, two chromatophores (yellow, brown, or colorless), starch and oils as reserve food. Examples: Chilomonas, Cryptomonas.
  • Euglenida: Thick pellicle, flagella, anterior gullet leading to a reservoir, numerous chromatophores (green or colorless), paramylon and oils as reserve food. Examples: Euglena, Peranema, Phacus, Copromonas.
  • Volvocida: Rigid cellulose covering (theca), no gullet, 2 to 4 flagella, cup-shaped green chromatophores, starch and oils as reserve food. Examples: Chlamydomonas, Volvax
  • Chloromonadida: Dorso-ventrally flattened, delicate pellicle, green chromatophores, oils as reserve food. Examples: Vacularia, Coelomonas, Gonyostomum.
  • Hypermastigida: Highly specialized, numerous flagella, kinetosomes arranged in circles, plates or rows. Mouth absent, food ingested by pseudopodia. Gut symbionts of termites and cockroaches. Examples: Lophomonas, Trychonympha.
  • Trichomonadida: 4 to 6 flagella, one trailing, parasites of vertebrates. Example: Trichomonas.
  • Dinoflagellida : Planktonic, naked, amoeboid or with thick cellulose theca, gullet present or absent, two flagella, yellow or brown chromatophores, starch or oils as reserve food. Some display bioluminescence. Examples: Noctiluca, Ceratium.
  • Opalinata: Covered with cilia-like flagella, 2 to many monomorphic nuclei, reproduction through symmetrical binary fission or syngamy of anisogametes, parasitic in frogs and toads. Examples: Opalina, Zelleriella.

Subphylum I. Sarcomastigophora

• Flagella or pseudopodia as locomotor organelles.
  • Class 1. Zoomastigophorea (Zooflagellata): Lack chlorophyll or chromatophores, primarily parasitic.
    • Rhizomastigida: Small, amoeboid, freshwater. Locomotion via 1-4 flagella and pseudopodia. Examples: Mastigamoeba, Dimorpha.
    • Kinetoplastida: No gullet, kinetoplast present, 1 to 4 flagella. Primarily blood parasites. Examples: Bodo, Leishmania, Trypanosoma.
    • Choanoflagellida: Free-living, solitary or colonial. A collar surrounds the base of a single flagellum. Examples: Proterospongia.
    • Diplomonadida: Bilaterally symmetrical, binucleate, with delicate pellicle and cytostome. Examples: Giardia, Hexamita.
  • Class 2. Sarcodina
    • Moves and captures food using pseudopodia.
      • Subclass (a) Lobosia: Pseudopodia as lobopodia.
        • Order 1. Amoebida: Naked, amoeboid, without skeleton. Nucleus with honeycomb lattice. Examples: Amoeba, Entamoeba, Pelomyza.
        • Order 2. Arcellinida (Testacida): Body housed within a single-chambered shell of pseudochitin with an opening for lobopodia. Examples: Arcella, Difflugia, Euglypha.
      • Subclass (b) Filosia: Pseudopodia as filopodia. Naked or with shell containing a single opening. Examples: Allogronia, Penardia.
      • Subclass (c) Granuloreticulosia
        • Order Foraminiferida: Large, multi-chambered, with calcareous shell and openings for reticulopodia. Examples: Globigerina, Elphidium (Polystomella).
    • Class 2. Actinopodea:
      • Pseudopodia primarily axopodia with axial filaments, extending radially.
        • Subclass (a) Heliozoia: Spherical protozoans, called "sun-animalcules." Axopodia radiate. Skeleton of siliceous scales or spines. Examples: Actinophrys, Actinosphaerium.
        • Subclass (b) Radiolaria: Naked or with central capsule separating ectoplasm and endoplasm. Reticulopodia, axopodia, or filopodia. Skeleton of siliceous spicules or strontium sulphate. Examples: Collozoum, Thalassicola.
        • Subclass (c) Acantharia: Imperforate, non-chitinoid central capsule without pores. Skeleton of strontium sulphate. Axopodia as pseudopodia. Examples: Acanthometra.
        • Subclass (d) Proteomyridia: Pseudopodia are filopodia, mostly parasites on algae. Examples: Vampyrella, Pseudospora.
    • Class 3. Piroplasmea: Small parasites in red blood cells of vertebrates. Examples: Babesia (formerly grouped with Sporozoa, but species lack spore production).

Subphylum II. Sporozoa

• Lack locomotor organelles. Spores often present. Exclusively endoparasites.
  • Class 1. Telosporea:
    • Spores lack polar capsules and filaments.
      • Subclass (a) Gregarinia:
        • Mature trophozoites large, extracellular in host's gut and body cavities.
        • Each spore yields eight sporozoites.
        • Parasites of invertebrates.
        • Examples: Monocystis, Gregarina.
      • Subclass (b) Coccidia / APICOMPLEXA:
        • Mature trophozoites small and intracellular.
        • Each oocyst produces numerous sporozoites.
        • Blood or gut parasites of vertebrates.
        • Examples: Eimeria, Isospora, Plasmodium.
    • Class 2. Toxoplasmea:
      • Example: Toxoplasma.
    • Class 3. Haplosporea:
      • Spore cases present. Only asexual reproduction.
      • Example: Ichthyosporidium.

Subphylum III. Cnidospora

• Spores possess polar filaments.
  • Class 1. Myxosporidea:
    • Large spores derived from multiple nuclei.
    • Two or three-valved spores.
    • Parasites, primarily in fishes.
    • Examples: Myxidium, Myxobolus, Ceratomyxa.
  • Class 2. Microsporidea:
    • Small spores, developed from a single nucleus.
    • Univalved spore membrane.
    • Intracellular parasites in arthropods and fishes.
    • Example: Nosema.

Subphylum IV. Ciliophora

• Cilia present as locomotor and feeding organelles at some stage of the life cycle.
• Two types of nuclei (dimorphic) – macronucleus and micronucleus.
  • Class Ciliata (Infusoria):
    • Subclass (a) Holotricha:
      • Order 1. Gymnostomatida: Large ciliates lacking oral ciliature. Cytostome opens directly. No vestibule.
        • Examples: Coleps, Didinium, Prorodon, Dileptus.
      • **Order 2. **
    • Subclass (d) Spirotrichia:
      • Reduced body cilia.
      • Buccal cilia well-developed.
      • Definite mouth (cytostome) and gullet present.
        • Order 1. Heterotrichida: Body cilia short. Uniform or absent.
          • Examples: Stentor, Bursaria, Spirostomum.
        • Order 2. Oligotrichida: Body cilia reduced or absent. Buccal membranes prominent.
          • Examples: Strombidium, Halteria.
        • Order 3. Hypotrichida: Dorso-ventrally flattened. Fused cilia forming ventral cirri.
          • Examples: Euplotes, Stylonchia.

Explore the fascinating world of protozoa with this quiz. Test your knowledge on the characteristics, locomotion, nutrition, and reproduction of these unicellular organisms. Dive into the microscopic features that define these primitive animals!