The Collaborative International Dictionary of English v.0.48:

Cyclostomi \Cy*clos"to*mi\ (s?-kl?s"t?-m?), n. pl. [NL. See
   Cyclostomata.] (Zool.)
   A glass of fishes having a suckerlike mouth, without jaws, as
   the lamprey; the Marsipobranchii.
   [1913 Webster]