The document discusses nonvertebrate chordates and fish. It states that tunicates and lancelets are the two groups of nonvertebrate chordates. It defines chordates as animals that have a nerve cord, notochord, pharyngeal pouches and a tail extending past the anus. The document also notes that fish are aquatic vertebrates that mostly have paired fins, scales and gills, and that the evolution of jaws and paired fins were important developments for fish. It discusses adaptations for aquatic life in fish and classifies all living fish into three groups: jawless fish, cartilaginous fish, and bony fish based on their internal structure.