The various forms of Eubacteria : Eubacteria has a definite form and shape. They are classified as given below:
(a) Cocci : They are oval or spherical in shape. When they occur singly, they are called Micrococcus;if in pairs Diplococcus; if in a chain, streptococcus; and if occur in clusters, staphylococcus. Shape of bacteria may change according to time, habitat and medium. This characteristic of bacteria is known as pleomorphism e.g., Azotobacter.
(b) Bacilli: They are rod-like, with or without flagella. Flagella may be present at one or both the ends or around cells. Bacteria may occur singly, Bacillus; or in pairs, Diplobacillus or may form filaments, Streptobacillus.
© Vibrio : They are small and curved like commas. These are mostly motile. These have a flagellum at one end.
(d) Spirillum : These are twisted like a screw. They have flagella at one end or both the ends. Certain bacteria possess flagella for locomotion. The bacterial flagellum is made of a single protein molecule only.