Coccus (plural cocci or coccuses) can be used to describe any bacterium that has a spherical shape. It is one of the three distinct types of bacteria shapes, the other two being bacillus (rod-shaped) and spirillum (spiral-shaped) cells. Coccus is an English loanword of a Neolatin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning "berry".
Like all bacteria, each single coccus bacterium is an entire living organism. And some species exist in groups of cells. If they do group together, the patterns they arrange themselves in are given certain names based on the shape. Diplococci are arranged in two-cell pairs; these may represent several different genera. Bacteria in the Streptococcus genus are arranged in chains. Bacteria in the Sarcina genus typically form a cuboidal arrangement of eight cells. Staphylococcus is a genus of bacteria characterized by cells arranged in tetrad clusters (four cells in a square formation) or large, often irregular, grape-like clusters. While groups of cells together form these characteristic shapes, the individual bacterial cells themselves will appear as distinct circles within the chain or cluster.
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