flagellum
From ZooTerms (Dictionary of Invertebrate Zoology)
flagellum (noun; plural flagellums, flagella; Latin flagellum, whip): 1. Any of various whiplike appendages.
2. A protoplasmic process, longer than a cilium, whose movements usually effect locomotion of the cell.
3. The whip-like tip of the male copulatory organ in some invertebrates.
4. (Arthropoda: Crustacea) The multiarticulate distal portion of the antennule, antenna, or exopod.
5. (Arthropoda: Insecta) The distal portion of an insect antenna beyond the second segment (pedicel)
See also: flagellomere. 6. (Porifera) A long projection from a cell, used as a propeller.
