Bacilli= rod shaped
cocci = round spheres

Bacilli have a large surface area that helps them take in nutrients, but they may dry out easily. Cocci do not dry out as quickly and retain water, but they absorb nutrients slowly.

An example of cocci is Staphylococcus hominis, and it occurs commonly on human and animal skin harmlessly, but it may occasionally cause infection in patients with weak immune systems. An example of bacilli is Escherichia coli, and these live in the intestines of animals and decompose undigested food. They are usually helpful or harmless, but some may cause food poisoning in their hosts.