How are bacteria classified on the basis of morphology?

Size of bacteria ranges between 2.0 $\mathrm{\mu }$m - 5 $\mathrm{\mu }$m. Rigid cell wall determines the shape of bacterial cell.

Classification of bacteria based on shape :
i) Cocci  - round or spherical cells.
ii) Bacilli  -  rod shape.
iii) Vibrios  -  comma shape.
iv) Spirillum  -  cells that have more than one complete twist.
v) Pleomorphic  -  not having definite shape.
Eg: Acetobacter
vi) Filamentous  -  thread like.
Eg: Actinomycetes, Beggiotoa