Cyclostomata

Cyclostomi, often referred to as Cyclostomata (, from Ancient Greekκύκλος (kúklos), meaning "circle", and στόμα (stóma), meaning "mouth", and thus, "circular mouth") is a superclass of vertebrates that comprises the living jawless fishclasses: the lampreys and hagfishes. Both groups have jawless mouths with horny epidermal structures that function as teeth called ceratodontes, and branchial arches that are internally positioned instead of external as in the related jawed fishes.