11. Fishes are abundant, diverse, and include four classes.
12. Aquatic adaptations include a streamlined body, lightweight bones, fins and tails, and ways to maximize extraction of oxygen from water. They are ectotherms, with the environment controlling body temperature.
13. Hagfishes and lampreys are two types of jawless fishes. The hagfishes are more primitive, and secrete slime. Lampreys have a sucking mouth.
14. Ostracoderms were jawless fishes, now extinct. The placoderms are an extinct class that may have originated jaws.
15. The cartilaginous jawed fishes include chimaeras, skates, rays, and sharks. Sharks detect vibrations from prey with a lateral line system.
16. The bony jawed fishes account for 96% of extant fish species. They include ray-finned fishes, lungfishes, and lobe-finned fishes. Bony fishes have lateral line systems and also swim bladders, which enable them to control their buoyancy.
17. Amphibians retain some characteristics of fishes, yet are adapted to life on land. They have denser bones, lungs, four limbs, different senses emphasized, and more powerful circulatory systems. Chromatophores enable some of them to change color.