A virion is an entire virus particle. A virion can also be defined as the extracellular infective form of a virus. It consists of an RNA or DNA genome surrounded by a protein capsid and, in some virus families, an external lipid envelope derived from the modified host cell membrane. In most animal and plant virus families, non-enveloped or “naked” virions show either icosahedral or helical symmetry. In turn, enveloped virions as well as those that infect bacteria and archaea usually show complex shapes. Virions typically range in size from about 20 to 300 nm, although certain viral families that infect amoebas produce larger virions.