Coccus is the name given a single bacterium that stands and functions alone. A coccus is generally spherical although these bacteria may also be slightly elongated, kidney bean shaped, or helmet shaped.
Diplococci are cocci that remain attached to another cell, often due to an incomplete budding process after cellular division. Neisseria gonorrhoeae, a bacterium that causes multiple diseases in humans, grows as diplococci.
Staphylococci are a species of cocci that remain attached after division and form sheets or clusters, similar to grapes. Each form of Staphylococcus lacks an organized shape. Staphylococcus aureus, responsible for many serious skin infections, grows in this form.
Streptococci are a form of cocci that form a chain of cells after failing to divide completely. The Streptococcus species, responsible for a variety of human disease including strep throat, grow in a chain form.
Sarcina are a form of cocci that remain in groups of eight after division, forming a three-dimensional cube. Bacteria in the Sarcina genus are often found in soil and water and are typically parasitic.
Tetrads are a group of four cocci that form a square. Within this classification is the common microorganism Micrococcus luteus found in dust, air, soil and the skin of mammals.