Final answer:
Mollusks have two circulatory systems: open and closed. In an open system, the fluid hemolymph is pumped through a blood vessel that empties into the body cavity. In a closed system, the heart pumps blood through vessels separate from the interstitial fluid of the body.
Step-by-step explanation:
Mollusks have two different circulatory systems: open and closed. In an open circulatory system, a fluid called hemolymph is pumped through a blood vessel that empties into the body cavity.
Hemolymph returns to the blood vessel through openings called ostia. Arthropods like bees and most mollusks have open circulatory systems. On the other hand, some mollusks, such as squids, have evolved a closed circulatory system. In a closed system, the heart pumps blood through vessels that are separate from the interstitial fluid of the body.