Class Agnatha Jawless fish. Living species include lampreys and hagfish. Ostracoderms – armor plates of bony tissue Placoderms – mineral hardened backbone and jaw Significant because they may represent the ancestor of bony fish/sharks. Key Innovations Bony Fish Bone tissue with a vertebrae part of inner skeleton, paired with muscle segments Jaws started trend towards more complex sensory organs and nervous systems Paired fins Key Innovations Bony Fish Gills – large surface area for water to diffuse into blood vessels Don't function out of water Lungs – supplemented and then replaced gills Increase effiency Characteristics of Cartilaginous Fish Class Chondrichthyes includes sharks, rays and their close relatives. jawed fish, that lack a swim bladder, and cartilaginous skeletons. 5-7 gill silts, stream lined body “conveyor belt” of teeth. Modified scales Sharks and Rays 5-6 Sharks and rays have other interesting characteristics: lateral lines – lines of sensory hair along the length of the body, detect water motion and vibrations. electroreception – the ability to sense minute electricity created by muscles and nerves. ampullae of Lorenzini - visible pits near their snouts used to detect the electrical current. Osteichthyes Ray-finned fish – flexible fin with support from skin and scales Bony endoskeleton Swim bladder – exchanges gases with blood to help with floatation (gulp air) Characteristics of Bony Fish Characteristics for life on the reef and for life in the open ocean: 5-8 lateral lines that detect water motion and vibrations. open ocean fish have a torpedo-like streamlined shape to minimizes drag and turbulence. Lobe-Finned Coelacanths only surviving group Ventral fin are extensions of body with skeletal support Lungfish Have gills and 1-2 small outpouching of gut wall Sacs help take in O2 and remove CO2 Must surface and gulp air (will drown if held under water) Ancestor to tetrapod??