Both zoospores and gametes of the chytrids are mobile by their flagella, one whiplash per individual. The thalli are coenocytic and usually form no true mycelium (having rhizoids instead). Some species are unicellular. Like other fungi, the cell wall in chytrids is composed of chitin.
Some chytrid species are known to kill amphibians in large numbers. The actual process, however, is unknown. The infection is referred to as chytridiomycosis. Decline in frog populations led to the discovery of chytridomycosis in 1998 in Australia and Panama. Chytrids may also infect plant species; in particular, maize-attacking and alfalfa-attacking species have been described. Synchytrium endobioticum is an important potato pathogen.
The earliest fossils of chytrids are from the Scottish Rhynie chert, a Devonian-age locality with anatomical preservation of plants and fungi. Among the microfossils are chytrids preserved as parasites on rhyniophytes. These fossils closely resemble the genus Allomyces.