The whip-like appendages that arise from the outer layer of the cytoplasm are called flagella. The stiff flagella are called fimbriae. It is composed of flagellin protein. Its length is 4-5 nm. Flagella help bacteria to move. Each flagella has three segments. Basal body, hook and filament. Bacteria with flagella are called Tricus and those without flagella are called Atrichous.