Protist Diversity: Key Concepts

• Lineages of Protists: There are two primary lineages of protists:

  • Unikonta: Includes Amoebozoa and Opisthokonta, which encompasses animals and fungi.

  • Bikonta: Includes Excavata, Plantae (Archaeplastida), SAR (Stramenopila, Alveolata, Rhizaria), Cryptista, and Haptista.

• Synapomorphies: Characteristics that define each lineage; these are fundamental to understanding protist diversity and each lineage includes representatives of biological importance.

Unikonta Lineage

Amoebozoa

• Characteristics:

  • Lack of cell walls.

  • Exhibit lobed pseudopodia, utilizing cytoplasmic streaming.

• Examples:

  • Lobose Amoebas:

    • Entamoeba histolytica: A pathogenic species.

    • Naegleria fowleri: A free-living amoeba that can cause infections.

  • Cellular Slime Molds:

    • Dominant haploid stage, e.g., Dictyostelium discoides.

    • Free-living amoeboid cells gather when starved, forming a slug-like organism, then produce spores.

  • Plasmodial Slime Molds:

    • Diploid dominant, forming a multicellular structure during part of their lifecycle.

Opisthokonta

• Characteristics:

  • Reproductive cells have a single flagellum.

  • Includes kingdoms of fungi and animals.

Bikonta Lineage

Excavata

• Characteristics:

  • Feature a feeding groove and many lack mitochondria.

  • Primarily motile with flagella.

• Examples:

  • Parabasalids: Live inside animals; e.g., Trichomonas vaginalis (causes trichomoniasis).

  • Diplomonads: Have two nuclei; e.g., Giardia (cause of giardiasis).

  • Euglenoids: Freshwater plankton, many are photosynthetic; e.g., Euglena gracilis.

  • Trypanosomes: Have a kinetoplast; e.g., Trypanosoma brucei (causes African Sleeping Sickness).

Archaeplastida (Plantae)

• Characteristics:

  • Possesses chloroplasts with a double membrane from primary endosymbiosis.

  • Important for primary production in ecosystems.

• Examples:

  • Glaucophyte Algae.

  • Red Algae.

  • Green Algae.

  • Land Plants.

Rhizaria

• Characteristics:

  • Lacks cell walls and exhibits calcium carbonate shells.

  • Threadlike pseudopodia for feeding or movement.

• Examples:

  • Foraminiferans: Create calcium carbonate shells, contributing to limestone formation over time.

  • Radiolarians: Possess silica skeletons.

  • Cercozoans: Recognized mainly through modern molecular phylogenies based on rRNA studies.

Alveolata

• Characteristics:

  • Defined by sac-like structures called alveoli beneath the plasma membrane.

• Examples:

  • Dinoflagellates: Can cause harmful algal blooms; some are bioluminescent and symbiotic with corals (zooxanthellae).

  • Ciliates: E.g., Paramecium caudatum.

  • Apicomplexans: Parasitic; e.g., Plasmodium (causes malaria).

Stramenopila

• Characteristics:

  • Possess two flagella with hollow hair-like extensions.

• Examples:

  • Diatoms: Major primary producers; contribute significantly to ocean photosynthesis; have silica cell walls, creating diatomaceous earth.

  • Oomycetes (Water Molds): Key decomposers in freshwater environments.

  • Brown Algae: Includes multicellular forms like seaweeds and kelp.