With diameters or lengths in the range of 1–10 µm, prokaryotic cells are generally smaller than eukaryotic cells, whose diameters are usually in the range of 10–100 µm. Each individual prokaryote is a single cell, but many types of prokaryotes form chains or small clusters of cells, and some occur in large clusters containing hundreds of cells. In this section we will first consider the features shared by cells in the domains Bacteria and Archaea. Then we will examine structural features that are found in some, but not all, prokaryotes.