Source : Webster's Revised Unabridged Dictionary (1913)

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