Atail like structures which allows certain unicellular organisms to move

The answer is flagella.

Flagella are tail-like structures which allow some unicellular organisms to move. Although their primary function is in locomotion, they can also serve as sensory organelles that are sensitive to chemicals or temperature of the environment. They can be found in all three domains - bacteria, archaea, and eukaryota:
- Bacterial flagella have a rotary motor at the base of each filament turning clockwise or counterclockwise
- Archaeal flagella look like bacterial flagella.
- Eukaryotic flagella are structurally complex cellular projections.