That is, bacteria are procaryotes. Not to be confused with true algae which are eucaryotes. Different types may be unicellular or multicellular. Virus Viruses are infectious agents, so small they pass through filters known to stop bacteria . Viruses are not cellular and therefore are classified as neither procaryotes nor eucaryotes.
Viruses are obligate, intracellular parasites of cellular organisms.
The first time a binomial is used, the genus name is spelled out. There after it is abbreviated. It is a good idea to abbreviate non-ambiguously. For example, the first time you use Escherichia coli , you use both names spelled out. From then on you use E. coli instead.