Raven Johnson Biology Chapter 42 Answers to Review Questions 1. In the vertebrates, bony vertebrae replace the notochord. The nerve cord is protected within a U-shaped groove in the vertebrae.
Jaws are a modification of one or more gill arches.
Teeth are modified from skin. The bony skeleton weighs more so that fish tend to sink with it. An air bladder provides buoyancy to counter the sinking. This bladder developed from a lunglike outpocketing of the pharynx. The lateral line system is the ability to detect changes in the pressure of water and sense movements of objects.