Biology · ANIMAL KINGDOM

Observe the cartilaginous fishes illustrated in Figure 4.19. Which combination of anatomical features correctly explains why these organisms must swim constantly without resting?

1. A
   Absence of an operculum forces continuous movement for water filtration
2. B
   Presence of placoid scales generates high frictional resistance in water
3. C
   Absence of an air bladder forces continuous swimming to prevent sinking
4. D
   Presence of a persistent notochord prevents flexible body undulating motion