n.
Spherical bacterium.
Many species have characteristic arrangements that are useful in identification. Pairs of cocci are called diplococci; rows or chains, streptococci (see streptococcus ); grapelike clusters, staphylococci (see staphylococcus ); packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads. These characteristic groupings occur as a result of variations in the reproduction process.