In chytrids, the globular fruiting body forms multicellular, branched hyphae; other species are single-celled. Chytrids are thought to be one of the earliest fungal groups to diverge from other fungi. This phyla of fungi contains 1,000 species. Chytrids fulfill various roles in the ecosystem: some are decomposers, some are parasites. Other chytrids have mutualistic relationships with organisms, for example, sheep and cattle have anaerobic chytrids in their digestive tracts, which aid in digestion. Chytrids have characteristics in common with other fungi such as chitinous cell walls, enzymes and several metabolic pathways. Chytrids produce zoospores with a single flagellum, making them capable of active movement through water. Because of this, early taxonomists classified them as protists. According to rRNA sequences in ribosomes, the chytrids are the most primitive of the fungal phyla.