The Class Chytridiomycetes is a group of simple, mostly aquatic fungi known as chytrids. They are typically microscopic and produce motile spores with flagella, a unique feature among fungi. Chytrids can be saprophytic, decomposing organic matter, or parasitic, infecting plants, algae, and amphibians (notably causing declines in amphibian populations through chytridiomycosis). They represent some of the most primitive fungi, lacking complex multicellular structures like mycelium found in higher fungi.