The Collaborative International Dictionary of English v.0.48:

Galley-worm \Gal"ley-worm`\, n. [Prob. so called because the
   numerous legs along the sides move rhythmically like the oars
   of a galley.] (Zool.)
   A chilognath myriapod of the genus Iulus, and allied
   genera, having numerous short legs along the sides; a
   milliped or "thousand legs." See Chilognatha.
   [1913 Webster]