Final answer:
The circulatory system of cephalopods is more efficient than other mollusks because it has branchial hearts at the base of each gill.
Step-by-step explanation:
The circulatory system of cephalopods, such as squids, is more efficient than other mollusks because it has accessory or branchial hearts at the base of each gill. In cephalopods, the branchial hearts help to pump oxygenated blood to the gills for efficient gas exchange.
This allows cephalopods to have a closed circulatory system that enables them to move rapidly and catch prey. On the other hand, most mollusks have open circulatory systems with simple hearts that are less efficient.