The Collaborative International Dictionary of English v.0.48:

Cyclostomata \Cy`clo*stom"a*ta\ (s?`kl?-st?m"?-t?), Cyclostoma
\Cy*clos"to*ma\ (s?-kl?s"t?-m?), n. pl. [NL., fr. Gr. ky`klos
   circle + sto`ma, -atos mouth.] (Zool.)
   A division of Bryozoa, in which the cells have circular
   apertures.
   [1913 Webster] Cyclostome

WordNet (r) 3.0 (2006):

Cyclostomata
    n 1: primitive jawless aquatic vertebrate: lampreys; hagfishes
         [syn: Cyclostomata, order Cyclostomata]