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4: "Protists"

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    Protists are not a phylogenetically related group of organisms. In the very recent past--and still in many textbooks today--eukaryotic organisms were lumped into four groups: Animals, Plants, Fungi (only separated from plants since around the same time we figured out how to get to THE MOON), and Protists. Organisms were classified as belonging to Kingdom Protista by saying "Well, it isn't an animal, plant, or fungus," so it isn't surprising to find out that these organisms are not actually genetically related to each other. Protists encompass an incredibly diverse group of organisms that span many evolutionary lineages. Below are a few supergroups discussed in Pawlowski (2013) that include groups you'll find in the "Protists" chapter of this book:

    • Stramenopiles: Includes the water molds, brown algae, and diatoms
    • Archaeplastida: Includes the red and green algae (and plants!)
    • Amoebozoa: Includes the slime molds
    A phylogeny for eukaryotes published in Pawlowski (2013), an open-access paper
    Figure from Pawlowski (2013).

    • 4.1: Slime Molds
      Slime molds encompass organisms from several lineages. Here, we look at two major types. Cellular slime molds are groups of unicellular amoebae that collaborate to form fruiting structures to disperse spores. This group includes Dictyostelids and Acrasids. Plasmodial slime molds (classified under Myxogastria or Myxomycetes) form a large, multinucleate amoeba with no cell wall that will eventually wall off individual nuclei to form spores.
    • 4.2: Water Molds
      Water molds belong to the phylum Oomycota. These fungus-like organisms have cellulose cell walls, a diplontic life cycle, and zoospores with one whiplash and one tinsel flagellum. They are more closely related to brown algae and diatoms (in a group called the Heterokonts) than to Kingdom Fungi.
    • 4.3: Brown Algae
      Brown algae are a lineage of primarily marine, multicellular heterokonts. Rockweeds and kelps belong to this group.
    • 4.4: Diatoms
      Diatoms are another photosynthetic lineage of heterokonts. They are unicellular organisms surrounded by a silica frustule. Diatoms are an incredibly diverse group of unicellular organisms containing anywhere from 20,000 to 2 million species.
    • 4.5: Red Algae
      The red and green algae are descendents of the primary endosymbiosis event that resulted in the first chloroplast. Red algae are primarily marine and can be unicellular or multicellular. They have a complex alternation of generations life cycle with an extra diploid phase.
    • 4.6: Green Algae
      The nature of the evolutionary relationships between the green algae are still up for debate. As of 2019, genetic data supports splitting the green algae into two major lineages: chlorophytes and streptophytes. The streptophytes include several lineages of green algae and all land plants. Streptophytes and chlorophytes represent a monophyletic group called Viridiplantae (literally “green plants”).

    This page titled 4: "Protists" is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Maria Morrow (ASCCC Open Educational Resources Initiative) .

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