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An introduction to the protists, a diverse group of organisms consisting of approximately 160,000 living and extinct species. Mostly single-celled eukaryotes, they inhabit aquatic or moist environments and can be classified into three main types: algae, protozoa, and slime & water molds. In this document, we will discuss examples of each type, including their characteristics, habitats, and classifications.
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(160,000 living & extinct species; estimates to 200,000 actual species) mostly single-celled, eukaryotes restricted to aquatic, or moist environments: oceans, ponds, lakes, rivers, damp soil, tree bark, snow, etc.; some species are colonial or multicellular; autotrophs & heterotrophs; with or without cell walls; most motile. Genetic analyses have dramatically changed the classification scheme if this group of organisms. In this course we will discuss examples of three main types of protists; algae, protozoa and slime & water molds.
(22,000 living species) diverse group of mostly unicellular protists, some colonial or multicellular; restricted to aquatic or moist environments: oceans, ponds, lakes, rivers, soil, bark, snow, etc.; photosynthetic with chloroplasts containing chlorophyll and other pigments, most motile; most with cell wall; cell walls of cellulose, proteins,, silica or other materials classified according to their kinds of photosynthetic pigments and composition of cell wall Fire Algae (Dinoflagellates; Phylum Pyrrhophyta, 2100 species) unicellular, many symbiotic as zooxanthellae; some produce cell walls of armored plates, blooms produce toxic red tides, bioluminescent Diatoms (Glass Algae; Phylum Chrysophyta, 28000 living & extinct species) most abundant group of algae; unicellular, radial symmetry, cell walls contain silica; common in freshwater and oceans; source of diatomaceous earth; gliding movement, Euglenas (Phylum Euglenophyta, 1000 species) unicellular, only algae without a cell wall; mainly in eutrophic ponds and pools, motile by flagellum Green Algae (Phylum Chlorophyta, 9000 species) aquatic and terrestrial; some form lichens with fungi; diverse body forms, mostly unicellular and colonial, some filaments or sheets; probably gave rise to plant kingdom; motile by flagella, cell wall of cellulose; energy stored as starch in vacuole Red Algae (Red Sea Weeds; Phylum Rhodophyta, 4000 species) mostly multicellular, body of filaments or sheets attached to substrate by holdfast; some excrete calcium carbonate=coralline algae; found in warm tropical oceans; thick starchy cell walls yield commercial quantities of agar and carrageenan Brown Algae (Brown Sea Weeds; Phylum Phaeophyta, 1500 species) all multicellular, some up to 60 m long; body differentiated into blade, stipe, floats and holdfast; found in cooler marine waters especially intertidal areas; used as food especially in SE Asian countries
mostly single celled or colonial, heterotrophs, nonphotosynthetic, no chloroplasts; lack cell wall, heterotrophic nutrition, most are motile; classified according to type of motility Amoebas (Phylum Sarcomastigophora) 44,000 living & extinct species simplest of protozoan protists; ‘amoeba’ means to change form - move by means of false feet (pseudopodia) some species produce shells of silica (radiolaria) or calcium carbonate (foraminiferans) Flagellates (Phylum Sarcomastigophora) 1,500 species most are symbiotic with other organisms, a few are pathogens; move by one or more flagella Ciliates (Phylum Ciliophora) 8,000 species the largest, most diverse group of protozoans; ;most are freeliving, motile by cilia; great diversity of size, shape and internal organelles Apicomplexans (Phylum Apicomplexa) 5,000 species all are nonmotile parasites with complex life cycles that alternate between sexual and asexual reproduction
Superficially resemble fungi; nonphotosynthetic heterotrophs with body of hyphal filaments; produce flagellate reproductive cells; some have cell wall of cellulose, others of chitin. Plasmodial Slime Molds (Phylum Myxomycota) (500 sp) feeding stage is motile, plasmodial stage; fruiting body a sporangium producing swarm cells and myxamoeba Cellular Slime Molds (Phylum Acrasiomycota) (65 sp) feeding stage is unicellular amoeboid like cells; fruiting body is multicellular pseudoplasmodium (=slug) producing spores. Water Molds (Phylum Oomycota & Chytridiomycota) (170 sp) aquatic multicellular heterotrophs; mycelium of threadlike hyphae; most are saprobes others are parasites of plants, animals and other fungi; mostly aquatic, a few are terrestrial