Protozoa (Animal-like Protists)

• Protozoa


  Motile eukaryotic unicellular protists
• Protozoa

  • Found in diverse moist habitats, susceptible to desiccation
  • Most are free-living in fresh water, marine environments, or terrestrial habitats like decaying matter and soil; some are parasitic
  • Integral to plankton and important in biochemical and molecular studies
  • Many protozoa exhibit chemoheterotrophic nutrition
• Types of protozoan nutrition

  • Holozoic (phagocytosis)
  • Saprozoic (absorption)
• Protozoan movement

  • Via pseudopodia, flagella, or cilia; some are non-motile
• Protozoan reproduction

  • Mainly through asexual methods like binary fission
  • Sexual reproduction, such as conjugation, occurs in some species, especially among ciliates
• Protozoa lack chitin or collagen in cell walls
• Phylum Rhizopoda (Amoeboid Protists)


  Found worldwide in freshwater, saltwater, and abundant in soil; some are parasitic
• Amoeboid movement


  • Simple amoebae exhibit amoeboid movement using pseudopodia
  • Lack definite shape; internal structures shift as they move
• Amoeboid feeding

  Engage in phagocytosis to engulf materials like algae, bacteria, and other protozoa; pinocytosis also occurs
• Amoeboid reproduction

  • Primarily by asexual binary fission; cyst formation is possible
• Types of amoebae

  • Some amoebae, like Arcella, form protective shells or tests
  • Foraminiferans and radiolarians are marine amoebae with diverse test and skeleton shapes
  • Symbiotic amoebae, like Endamoeba and Entamoeba, live in other animals
• Entamoeba histolytica


  A significant human parasite causing amoebic dysentery
• Naegleria and Acanthamoeba


  Free-living amoebae that can also cause diseases in humans and mammals
• Amoeba


  Uses pseudopodia for food ingestion and locomotion, constantly changing shape
• Amoeba structures


  • Endoplasm: Inner granular cytoplasm region
  • Ectoplasm: Thin, clear outer cytoplasm layer
  • Cell membrane: Surrounds the amoeba; also called plasma membrane
  • Nucleus: Darkly stained, biconcave disc-shaped structure
  • Contractile vacuole: Clear vacuole for water regulation
  • Food vacuoles: Contain digested food and enzymes
• Amoeba movement


  Achieved by extending pseudopodia, crucial for feeding and mobility; similar to cytoplasmic streaming in other cells
• Amoeba reproduction

  Asexual reproduction via binary fission; divides nucleus and cytoplasm to produce genetically identical daughter cells
• Phylum Ciliphora


  Largest protozoan phylum with about 8,000 species; unicellular, heterotrophic protists, ranging from 10 to 3,000 μm in length
• Ciliate movement and feeding

  • Use cilia for locomotion; cilia are arranged in rows or spirals and beat with an oblique stroke
  • Feeding involves cilia around the buccal cavity; food enters cytostome and digested in phagocytic vacuoles
• Ciliate structures

  • Typically have a large macronucleus and a smaller micronucleus
  • Contractile vacuoles regulate water balance, mainly in freshwater species
• Ciliate reproduction

  • Reproduce asexually by transverse binary fission and sexually by conjugation
• Ecological roles of ciliates


  • Free-living and symbiotic forms exist
  • Examples: Entodinium in cattle rumen, Nyctotherus in frog colon
  • Parasitic forms like Balantidium coli in mammalian intestines causing dysentery, and Ichthyophthirius in freshwater fish causing "ick" disease
• Paramecium


  Large, common ciliated protozoan found in freshwater with species ranging from 120-300 microns long; known for avoidance behavior, rotating up to 360 degrees in response to negative stimuli
• Paramecium structures

  • Cilia: Numerous, used for locomotion and food gathering
  • Pellicle: Thick outer covering through which cilia project
  • Trichocysts: Rodlike structures for defense and anchoring during feeding
  • Macronucleus: Large nucleus near the cell center
  • Micronucleus: Smaller nucleus involved in genetic exchange
  • Contractile Vacuoles: Clear vesicles for osmoregulation
  • Cytostome (Cell Mouth): Opening near posterior end for food intake
  • Cytopharynx: Tube extending from cytostome for food vacuole formation
  • Food Vacuoles: Contain and digest prey, discharged through cytopyge (anal pore)
• Paramecium feeding


  Heterotrophic, feeding on bacteria, yeasts, algae, and small protozoa via phagocytosis; specialized feeding apparatus includes oral groove, cytopharynx, and cytostome
• Paramecium reproduction

  • Asexual: Transverse fission where parent divides into two daughter cells
  • Sexual: Conjugation involves exchange of genetic material between two individuals followed by asexual reproduction
  • Occurs under optimal conditions, capable of multiple asexual reproductions per day
• Vorticella

  Sessile with an inverted bell shape; long, contractile stalk (spasmoneme) that coils like a spring; over 100 species
• Vorticella movement and feeding

  • Young are free-swimming; use cilia to create a water current to direct food (bacteria) to its mouth
• Vorticella reproduction

  • Binary fission along the longitudinal axis; one daughter cell keeps the stalk, and the other free swims and grows its own
• Didinium

  80-200 μm long with about 3,000 cilia arranged in bands; oval shape with a pointed snout (cytosome)
• Didinium feeding

  Carnivorous, preying on Paramecium; uses trichocysts to paralyze and devour Paramecium
• Didinium reproduction

  • Can reproduce sexually or asexually; encyst themselves if Paramecium is depleted
• Balantidium

  Anterior end more pointed than the posterior; cilia in oblique, longitudinal rows; macronucleus is large and sausage-shaped
• Balantidium transmission

  Via contaminated food or water containing ovoid cysts in host feces
• Podophyra


  Suctorian with no cilia in the adult stage; numerous long, contractile tubular tentacles for capturing prey
• Podophyra feeding


  Uses suctorial tentacles to capture and ingest other protozoa; prey remains alive as cytoplasm is sucked out
• Podophyra reproduction


  • Binary fission or budding into ciliated motile larvae; common in freshwater habitats, mainly feeding on ciliates
• Opalina


  Parasitic protozoan found in amphibians' digestive systems; flattened, leaf-shaped body covered with nearly equal cilia; lacks mouth and contractile vacuole, ingests via pinocytosis
• Opalina habitat


  Parasitic in cold-blooded vertebrates, including fishes
• Phylum Anticipoda


  Possess axopodia, a type of pseudopodium with an axial rod (axoneme) of microtubules; axopodia used primarily for feeding, not locomotion; many have silica-based tests