Final answer:
Bacilli and spirilla bacteria use flagella to move through liquid environments. These hair-like structures act like tiny whips, propelling the bacteria forward.
Step-by-step explanation:
Bacilli and spirilla bacteria use flagella, which are slender, hair-like extensions, to help them move. These structures are sometimes likened to tiny whips that propel the bacteria through liquids. The flagella are composed of flagellin protein subunits and extend outward from the cell, being driven by a motor called the basal body that is embedded in the plasma membrane. While cilia and pili, other hair-like structures found on some cells, serve different functions such as moving substances along the cell's surface or aiding in attachment to surfaces, it is the flagella that are particularly associated with bacterial locomotion.