In the subdivision Mastigomycotina which comprises two classes, the fungi produce motile spores, called zoospores, with one or two flagella.
The fungi class chytridiomycetes (the chytrids, or water molds) includes three orders of fungi that produce asexual zoospores with a single posterior whiplash flagellum in a sporangium, or, more specifically, a zoosporangium. Most species are microscopic, and many grow as parasites within the cells of algae, other fungi or higher plants. The cells are coenocytic (multinuclear) and enclosed in rigid walls containing chitin, except for some that grow as plasmodia within their host. The chytrids characteristically grow as sac-shapped cells with tapering, rootlike extensions, called rhizoids, that penetrate the substratum of its host. In asexual reproduction part or all of the cell body is converted into zoosporangia, or sporangia-producing zoopores. Sexual reproduction leads to a thick walled, often dormant resting spore.
The class Oomycetes of the subdivision Mastigomycotina is a group of fungi (water molds and fish molds) that typically occur in freshwater streams and ponds or as parasites of higher plants. Many are saprobes, living off decayed matter. Others cause damping off or rotting of seedlings; downy mildews of many plants, such as potato blight; and fish diseases. Oomycetes reproduce asexually by motile biflagellate zoospores with one whiplash and one tinsel flagellum. Pathogenic species such as Phytophthora infestants (the cause of potato blight) produce zoospores on specialized branches of the mycelium. The zoosparangia break free and are carried by wind or water to new hosts, whereupon zoospores may be released to initiate new infections or, under dry conditions, the sporangia may directly produce a mycelium.
Other Subdivisions:
Zygomycotina
Ascomycotina
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