The circulatory system of cartilaginous fish is characterized by which heart structure?

• A. Three-chambered heart
• B. Four-chambered heart
• C. Two-chambered heart
• D. No heart

Answer: (C)

Cartilaginous fish have a heart with two chambers—an atrium and a ventricle—and a single-circuit circulatory system. Blood moves from the body into the atrium, then into the ventricle, and is pumped to the gills for oxygenation before circulating to the rest of the body and returning to the heart. This setup means there isn’t a separate path for oxygenated versus deoxygenated blood, which is why a two-chambered heart best fits their physiology.

In contrast, a three-chambered heart (found in amphibians and some reptiles) provides partial separation of blood, and a four-chambered heart (in birds, mammals, and crocodilians) fully separates oxygenated and deoxygenated blood into two different circuits. No heart is not compatible with vertebrate circulation at all.