In lancelets, blood is circulated by which mechanism?

In lancelets, blood is circulated by which mechanism?

• A. A central heart
• B. Contractile blood vessels
• C. Rapid arteries in limbs
• D. Capillary beds only

Answer: (B)

In lancelets, there isn’t a true heart. Blood circulation is produced by the rhythmic contraction of vessels themselves—the contractile blood vessels along the body drive the flow. This vessel-walled pulsing moves blood through the dorsal aorta and into capillary networks, such as those in the pharyngeal region, before it returns. So the circulation is achieved by these contractile vessels rather than by a centralized pump, such as a heart. The other ideas—a central heart, rapid arteries in limbs (which lancelets lack), or capillary beds alone without a pumping mechanism—don’t fit what lancelets actually use to move blood.

In lancelets, there isn’t a true heart. Blood circulation is produced by the rhythmic contraction of vessels themselves—the contractile blood vessels along the body drive the flow. This vessel-walled pulsing moves blood through the dorsal aorta and into capillary networks, such as those in the pharyngeal region, before it returns. So the circulation is achieved by these contractile vessels rather than by a centralized pump, such as a heart. The other ideas—a central heart, rapid arteries in limbs (which lancelets lack), or capillary beds alone without a pumping mechanism—don’t fit what lancelets actually use to move blood.