conodont: 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
jawless vertebrate: eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms
reductase: an enzyme that catalyses the biochemical reduction of some specified substance