Which mollusks have an open circulatory system?

Which mollusks have an open circulatory system?

• A. Cephalopods
• B. Gastropods and bivalves
• C. Mollusk
• D. Radula

Answer: (B)

Open circulatory systems in mollusks are seen in the slower, less active groups, where hemolymph is pumped into body cavities and bathes organs before returning to the heart. Gastropods (snails and slugs) and bivalves (clams, oysters) fit this pattern well, so they have open circulatory systems. In these animals, blood (hemolymph) is not kept entirely within vessels, so it flows through sinuses and tissues at lower pressure. Cephalopods, by contrast, are mollusks with a closed circulatory system, featuring blood confined to vessels and supported by a more powerful heart arrangement to meet their high oxygen demands as active predators. The option describing a mollusk with a feeding structure (radula) or a vague term for all mollusks doesn’t specify circulation, while the combination of gastropods and bivalves accurately matches those with an open system.

Open circulatory systems in mollusks are seen in the slower, less active groups, where hemolymph is pumped into body cavities and bathes organs before returning to the heart. Gastropods (snails and slugs) and bivalves (clams, oysters) fit this pattern well, so they have open circulatory systems. In these animals, blood (hemolymph) is not kept entirely within vessels, so it flows through sinuses and tissues at lower pressure. Cephalopods, by contrast, are mollusks with a closed circulatory system, featuring blood confined to vessels and supported by a more powerful heart arrangement to meet their high oxygen demands as active predators. The option describing a mollusk with a feeding structure (radula) or a vague term for all mollusks doesn’t specify circulation, while the combination of gastropods and bivalves accurately matches those with an open system.