THE PROKARYOTIC CELL: BACTERIA. 1. There are three basic shapes of bacteria: coccus, bacillus, and spiral. 2. Based on planes of division, the coccus shape can appear in several distinct arrangements: diplococcus, streptococcus, tetrad, sarcina, and staphylococcus.acterial cell shape is determined primarily by a protein called MreB. MreB forms a spiral band – a simple cytoskeleton – around the interior of the cell just under the cytoplasmic membrane. It is thought to define shape by recruiting additional proteins that then direct the specific pattern of bacterial cell growth.