This shape varies significantly among species of bacteria and may be employed in the course of isolate identification. Two major shape classes are cocci and bacilli though there are many variations on these themes, additional distantly related shapes, as well as many variations on the degree to which cells separate or interact following their division. That is, from about 0.1 to about 600 m over a single dimension.
Bacteria vary in size as much as in shape.
Escherichia coli , a bacillus of about average size, is 1.1 to 1.5 m wide by 2.0 to 6.0 m long. Recently a huge bacterium has been discovered in the intestine of the brown surgeonfish, Acanthurus nigrofuscus . Epulopiscium fishelsoni grows as large as 600 m by 80 m, a little smaller than a printed hyphen. It is now clear that a few bacterium are much larger than the average eucaryotic cell. Epulopiscium fishelsoni is an example of a very big procaryote.