The Protists
(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.
Algae [Plant-Like Protists]
(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
