fish, in zoology, Vertebrate Zoology

Related Category: Vertebrate Zoology

The Jawless Fishes

The primitive fishes of the class Agnatha lack jaws and the paired pelvic and pectoral fins characteristic of more advanced fishes. This largely extinct class includes two living groups, the bloodsucking lampreys and the scavenging hagfishes. Fishes of the extinct class Placodermi were the first vertebrates to develop jaws and paired fins. These fish had bony skeletons and were covered with bony armor. A branch of this group probably gave rise to the two main modern classes of fish, the cartilaginous fish and the bony fish.