The Collaborative International Dictionary of English v.0.48:

Trochal \Tro"chal\, a. [From Gr. ? a wheel.] (Zool.)
   Resembling a wheel.
   [1913 Webster]

   Trochal disk (Zool.), the cephalic disk of a rotifer. It is
      usually surrounded by a fringe of cilia.
      [1913 Webster]