Closteriaceae
Desmidiaceae
Gonatozygaceae
Peniaceae
Desmids are the Desmidiales class of green algae, comprise around 40 genera and more than 10000 species, found mostly but not exclusively in freshwater. Most are unicellular, and are divided into two compartments separated by a narrow bridge or isthmus. Desmids assume a variety of highly symmetrical and generally attractive shapes, which provide the basis for their classification. Each has a single chloroplast, and no flagella. Sexual reproduction occurs through a process of conjugation, also found among the Zygnematales. These two groups are closely related, and may be united as the division Gamophyta . The desmids are sometimes treated as members of the Zygnematales, but more often given the separate order Desmidiales.