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.
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Cocci (singular - coccus, from the Latin coccinus (scarlet) and derived from the Greek kokkos (berry) ) are any microorganism (usually bacteria) whose overall shape is spherical or nearly spherical. Describing a bacterium as a coccus, or sphere, distinguishes it from bacillus, or rod. This is the first of many taxonomic traits for identifying and classifying a bacterium according to binomial nomenclature.