animal living wholly or chiefly in or on water

superclass of eel-shaped chordates lacking jaws and pelvic fins: lampreys; hagfishes; some extinct forms

extinct fish-like jawless vertebrate having a heavily armored body; of the Paleozoic

extinct jawless fish with the anterior part of the body covered with bony plates; of the Silurian and Devonian

extinct jawless fish of the Devonian with armored head

extinct small freshwater jawless fish usually having a heterocercal tail and an armored head; of the Silurian and Devonian

small (2 inches long) extinct eellike fish with a finned tail and a notochord and having cone-shaped teeth containing cellular bone; late Cambrian to late Triassic; possible predecessor of the cyclostomes

superclass of eel-shaped chordates lacking jaws and pelvic fins: lampreys; hagfishes; some extinct forms