Mollicutes are a class of bacteria that lack a peptidoglycan layer but have various cell shapes. They perform chromosome segregation and binary fission in a well-organized manner. Especially, species with polarized cell morphology duplicate their membrane protrusion at a position adjacent to the original one and move the new protrusion laterally to the opposite end pole before cell division. The featured various cell shapes of Mollicutes are supported by cytoskeletal structures composed of proteins. Recent progress in the study of cytoskeletons of walled bacteria and genome sequencing has revealed that the cytoskeletons of Mollicutes are not common with those of other bacteria. Mollicutes have special cytoskeletal proteins and structures that are sometimes not shared even by other mollicute species.