Question

General organization and distribution of cyclostomata

Answer 1

Cyclostomata is a group of agnathans that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have round mouths that lack jaws but have retractable horny teeth. The name Cyclostomata means "round mouths".[1][2] Their mouths cannot close due to the lack of a jaw, so they have to constantly cycle water through the mouth.