Final answer:
The circulatory system of cephalopods is more efficient because they have a closed circulatory system, allowing for efficient blood flow to meet their active lifestyle's high metabolic demands. This system is superior to the open circulatory system found in other, less active mollusks. Option A is the correct answer.
Step-by-step explanation:
The circulatory system of cephalopods is more efficient than that of other molluscs because they have evolved a closed circulatory system. This system allows their blood to be separated from the interstitial fluid, providing a more efficient means of transporting oxygen, nutrients, and waste throughout their body. With the closed system, cephalopods like squids can move rapidly to catch prey, which is essential for their active lifestyle. The presence of hemocyanin in their blood, which carries oxygen, complements the efficiency of their circulatory system.
Cephalopods are among the more active and complex mollusks, necessitating a more sophisticated approach to circulation compared to their relatives with open circulatory systems. An open system consists of pumping hemolymph through a blood vessel that empties into the body cavity and returns through openings called ostia. This is sufficient for less active mollusks, but not for the high metabolic demands of cephalopods. Cephalopods' closed circulatory system features a network of vessels that ensure rapid and directed blood flow, which is vital for their high metabolism and active predatory lifestyle.
It's interesting to note that the evolution of the circulatory system in animals demonstrates a progression from simple diffusion in sponges to more complex systems in vertebrates, highlighting the adaptation to increased oxygen needs through terrestrial living. The cephalopod circulatory system represents an advanced stage in this evolutionary process. Therefore, having a closed circulatory system is the reason for the increased efficiency in the circulatory system of cephalopods compared to other mollusks, making option A the correct choice.