Lesson Summary. Let's review. A flagellum is a whip-like structure that allows a cell to move. They are found in all three domains of the living world: bacteria, archaea, and eukaryota.While all three types of flagella are used for locomotion, they are structurally very different.The eukaryotic flagellum is a long, rod-like structure that is surrounded by an extension of the cell membrane like a sheath.t is similar to a cilium in structure, though cilia generally move in a back and forth motion, as opposed to the corkscrew movement of a flagellum. The eukaryotic flagellum is a long, rod-like structure that is surrounded by an extension of the cell membrane like a sheath.