cy·clo·stome 
(sīklə-stōm′)
(sīklə-stōm′)n.
Any of various fishes lacking jaws and true teeth and having a circular sucking mouth, including the hagfishes and the lampreys.
[From New Latin Cyclostomī and Cyclostomata, class names : CYCLO- + Greek stoma, stomat-, mouth.]
cy·closto·mate′ (sī-klŏstə-māt′, -mĭt) adj.