Smaller than flagella, they are microtubular, hairlike structures used by some single-celled organisms for locomotion through liquids. In addition, they cover the cells of certain tissues (e.g., the epithelium lining the lungs), and help these cells clear away fluids or particles. Structurally identical to flagella, the two terms are often used interchangeably. However, cilia are used when they are short and numerous, and flagella when they are relatively long and sparse.
See Cell, Cell locomotion, Cell migration, Cochlea, Cytoskeleton, Epithelium, Fallopian tubes, Filopdia, Flagella, Lamillipodia, Microtubules