Animal-Like Protists

• Protozoa


  • Single-celled eukaryotes
  • Sharing traits with animals
  • Feed by engulfing and digesting other organisms
  • Heterotrophs that are capable of movement
  • Thought to be ancestors of animals
• Protozoa


  • Various roles in food chains and webs: predators, herbivores, decomposers, parasites
  • Important food sources for larger organisms
• Classification of protozoa based on movement

  • Amoeboid: Amoeba moves using temporary extensions called pseudopods
  • Flagellate: Giardia moves with microscopic hair-like structures called flagella
  • Ciliate: Paramecium moves with short, hairlike vibrating structures called cilia
  • Sporozoan: Plasmodium doesn't move as adults
• Protozoan Taxonomy


  • Phylum Sarcomastigophora: Protozoans possessing flagella for movement
  • Phylum Labyrinthomorpha: Protozoans possessing labyrinthine membranes for locomotion
  • Phylum Apicomplexa: All parasites, includes Plasmodium and Toxoplasma
  • Phylum Microspora: Small intracellular parasites
  • Phylum Acetospora: Produce spores lacking polar capsules, parasitic in molluscs
  • Phylum Myxozoa: Tiny parasites, found in cold-blooded vertebrates and invertebrates
  • Phylum Ciliophora: Possess cilia, macronucleus, and micronuclei
• The kingdom Protista is a polyphyleric group that arose about 1.5 billion years ago from the Archaea
• Protozoa are both single cells and entire organisms. Organelles specialized for the unicellular lifestyle carry out many protozoan functions
• Many protozoa live in symbiotic relationships with other organisms, often in a host-parasite relationship
• Precise evolutionary relationships are difficult to determine for the protozoa due to sparse fossil record and uncertain ribosomal RNA sequence comparisons