Protozoa: Microscopic Animalcules Quiz

Protozoa: Microscopic Animalcules

• Organisms that are microscopic and acellular, lacking tissues and organs
• Exist as single cells or colonies
• All individuals in a colony are alike, except during reproduction
• Body is unicellular with one or more nuclei

General Characteristics

• Size: Small, usually not visible without a microscope
• Organization: Simplest and most primitive animals, with a protoplasmic grade of organization
• Nuclei: One or more nuclei, monomorphic (all alike) or dimorphic (two types)
• Symmetry: No symmetry, bilateral, radial, or spherical.
• Locomotion: Finger-like pseudopodia, whip-like flagella, hair-like cilia or absent.
• Nutrition: Holozoic (animal-like), holophytic (plant-like), saprozoic, or parasitic. Digestion is intracellular.
• Respiration and Excretion: Through the general surface or contractile vacuoles.
• Reproduction: Asexual through binary or multiple fission and budding. Sexual reproduction through conjugation of adults (hologamy) or fusion of gametes (syngamy).

Classification of Protozoa

• Divided into four subphyla: Sarcomastigophora, Sporozoa, Cnidospora, and Ciliophora

Sarcomastigophora

• Subphylum: Sarcomastigophora
  • Class 1. Mastigophora (flagellates):
    • Possess flagella for locomotion
    • Order 1. Cryptomonadida:
      • Have a rigid pellicle, two flagella, and a gullet reaching to the middle of the body.
      • Examples: Chilomonas, Cryptomonas
    • Order 2. Euglenida:
      • Thick and firm pellicle, one or two flagella, an anterior gullet leading to a reservoir.
      • Examples: Euglena, Peranema, Phacus, Copromonas
    • Order 3. Volvocida:
      • Rigid cellulose covering (theca), two to four flagella, no gullet.
      • Examples: Chlamydomonas, Volvox
    • Order 4. Chloromonadida:
      • Dorso-ventrally flat, delicate pellicle, a gullet, and numerous green chromatophores.
      • Examples: Vacularia, Coelomonas, Gonyostomum
    • Order 5. Hypermastigida:
      • Highly specialized with numerous flagella, kinetosomes arranged in circles, plates, or longitudinal or spiral rows.
      • Examples: Lophomonas, Trychonympha
    • Order 6. Trichomonadida:
      • Four to six flagella, one trailing flagellum, mostly parasites of vertebrates.
      • Example: Trichomonas
    • Order 7. Dinoflagellida:
      • Small, planktonic organisms, naked, amoeboid, or with a thick cellulose theca.
      • Examples: Noctiluca, Ceratium
  • Class 2. Zoomastigophora (zooflagellates):
    • Lack chlorophyll or chromatophores.
    • Primarily parasitic.
    • Order 1. Rhizomastigida:
      • Amoeboid, chiefly freshwater, locomotion by one to four flagella and pseudopodia.
      • Examples: Mastigamoeba, Dimorpha
    • Order 2. Kinetoplastida:
      • Possess a kinetoplast, one to four flagella, mostly parasitic.
      • Examples: Bodo, Leishmania, Trypanosoma
    • Order 3. Choanoflagellida:
      • A collar surrounding a single flagellum, free-living, solitary or colonial.
      • Example: Proterospongia
    • order 4. Diplomonadida:
      • Bilaterally symmetrical, binuclcate, with a delicate pellicle and a cytostome.
      • Examples: Hexamita, Giardia

Sarcodina (Rhizopoda)

• Subphylum: Sarcodina
  • Class 1. Rhizopodea:
    • Subclass (a) Lobosia:
      • Pseudopodia are lobopodia.
      • Order 1. Amoebida:
        • Naked, amoeboid, no skeleton, freshwater and free-living, many parasitic forms.
        • Examples: Amoeba, Entamoeba, Pelomyza.
      • Order 2. Arcellinida (Testacida):
        • Body enclosed in a one-chambered shell of pseudochitin, with an opening for pseudopodia.
        • Examples: Arcella, Difflugia, Euglypha.
    • Subclass (b) Filosia:
      • Pseudopodia are filopodia, naked or with a single-opening shell.
    • Subclass (c) Axopodia:
      • Pseudopodia are axopodia with axial filaments.
      • Example: Acanthometra
    • Subclass (d) Proteomyridia:
      • Pseudopodia are filopodia, mostly parasites on algae.
      • Examples: Vampyrella, Pseudospora
  • Class 2. Microsporidea
    • Small spores developed from one nucleus.
    • Intracellular parasites in arthropods and fishes.
    • Example: Nosema
  • Class 3. Piroplasmea
    • Small parasites in red blood cells of vertebrates.
    • Example: Babeisa

Sporozoa

• Subphylum: Sporozoa
  • No locomotor organelles.
  • All are endoparasites.
  • Spore formation is common.
  • Example: Plasmodium

Ciliophora

• Subphylum: Ciliphora
  • Class 1. Ciliata (Infusoria):
    • Subclass (a) Holotricha:
      • Body cilia simple, uniform, buccal cilia mostly absent.
      • Order 1. Gymnostomatida:
        • Large ciliates, no oral ciliature, cytostome opens directly, no vestibule.
        • Examples: Coleps, Didinium, Prorodon, Dileptus.
      • Order 2. Trichostomatida:
        • Vestibular but no buccal ciliature.
        • Examples: Balantidium, Colpoda.
      • Order 3. Chonotrichida:
        • No body ciliature, a spirally coiled apical funnel contains vestibular cilia.
        • Examples: Spirochona, Lobochona.
      • Order 4. Apostomatida:
        • Spirally arranged body cilia, cytostome midventral.
        • Example: Hyalophysa.
      • Order 5. Astomatida:
        • Body ciliation uniform, cytostome absent.
        • Examples: Anoplophyrya, Maupasella.
      • Order 6. Hymenostomatida:
        • Body ciliation uniform, buccal cavity ventral with ciliary membranes.
        • Examples: Colpidium, Paramecium.
    • Subclass (b) Peritricha:
      • Adults lack body cilia, apical end with buccal cilia.
      • Order: Peritrichida:
        • Examples: Vorticella, Carchesium.
    • Subclass (c) Suctoria:
      • Sessile and stalked body.
      • Young have cilia, adults have suctorial tentacles.
      • Order: Suctorida:
        • Examples: Acineta, Ephelota, Podophyra.
    • Subclass (d) Spirotrichia:
      • Reduced body cilia, buccal cilia well marked.
      • Order 1. Heterotrichida:
        • Body cilia are short, uniform, or absent.
        • Examples: Stentor, Bursaria, Spirostomum.
      • Order 2. Oligotrichida:
        • Body cilia reduced or absent, buccal membranes conspicuous.
        • Examples: Strombidium, Halterna.
      • Order 3. Hypotrichida:
        • Dorso-ventrally flattened, fused cilia forming ventral cirri.
        • Examples: Euplotes, Stylonchia

Example: Chlamydomonas

• A typical genus of the order Phytomonadida.
• Microscopic, unicellular, and solitary.
• Found in stagnant freshwater ponds.
• Ovoid or flattened body with a thick cellulose cell wall.
• Two long flagella arising from blepharoplasts.
• Cytoplasm contains a vesicular nucleus, cup-shaped chloroplast with a pyrenoid, a red stigma, a pair of small contractile vacuoles, and reserve food granules such as starch and oil droplets.
• Nutrition is mainly holophytic, but osmotrophic tendencies are also seen.
• Asexual reproduction is by binary fission, often in a palmella stage.
• Sexual reproduction occurs through conjugation.