Small, infectious, obligate intracellular nonliving molecular parasite. Have ss or ds genome of DNA or RNA. Multiplication requires host cell. Progeny are the vehicle of transmission of virus. Icosohedral virus (simple/complex) and helical virus. Spindle viruses are specific to archaea. (+) RNA = mRNA; (-) RNA = complimentary mRNA. Viruses are filterable & passageable. Envelope [...]