The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis (meaning "soft" or "pliable"), and cutis (meaning "skin"). They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size and have a very small genome size. They vary in form, although most have sterols that make the cell membrane somewhat more rigid. Many are able to move about through gliding, but members of the genus Spiroplasma are helical and move by twisting. The best-known genus in Mollicutes is Mycoplasma.
Many Mollicutes cause diseases in humans, attaching to cells in the respiratory or urogenital tracts, particularly species of Mycoplasma and Ureaplasma.
Phytoplasma and Spiroplasma are plant pathogens associated with insect vectors.
Whereas formerly the trivial name "mycoplasma" has commonly denoted any member of the class Mollicutes, nowadays it refers exclusively to a member of the genus Mycoplasma.
Read more about Mollicutes: Origin and Development To Parasitic Life, History of The Classification, Modern Taxonomy