The coccus bacteria (plural - cocci) are spherical, ellipsoidal or ovoid in shape. Coccus forms may exist singly (Micrococcus), in tetrads (Tetracoccus), in chains (Streptococcus) or in irregular grape-like clusters (Staphylococcus). A few cocci may occur in cubical packets of 8 or more cells (Sarcina).