A class of terrestrial fungi in the phylum Zygomycota, reproducing sexually with a zygospore and asexually by sporangiospore or conidium. The Zygomycetes are one of two classes of the phylum Zygomycota, the other being the arthropod-associated Trichomycetes. Zygomycetes can be distinguished by the production of sporangia (sacs) that undergo internal cleavage to produce multiple sporangiospores (see illustration) as opposed to the production of conidiospores as observed in most other groups of fungi (Ascomycota and Basidiomycota). A notable exception is the order Entomophthorales, which reproduces asexually by conidium formation. Zygomycetes are all microscopic with the exception of Endogone and relatives that produce a zygospore containing structure called a sporocarp. Zygomycetes are typically studied by first isolating them into pure culture on nutrient media. Sexual reproduction results in the formation of a thick-walled zygosporangium following the conjugation of morphologically relatively similar, undifferentiated gametangia (single-cell structures functioning as gametes). The gametangia may be derived from different (heterothallism) or the same (homothallism) thallus, or genetic individual.