Which heart structure is common to jawless, cartilaginous, and bony fishes?

Which heart structure is common to jawless, cartilaginous, and bony fishes?

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

Answer: (C)

Two-chambered hearts are typical in fishes, enabling a single circulatory loop. The heart has an atrium that receives blood and a ventricle that pumps it to the gills for oxygenation, after which blood flows through the body and returns to the atrium. This arrangement is shared by jawless, cartilaginous, and most bony fishes, making two chambers the common heart structure among these groups. There are exceptions, such as lungfishes, which have three chambers, but the standard pattern across the broad fish line is two chambers. The other heart designs are found in other vertebrates with more complex circulations, and a lack of a heart is not applicable to fishes.

Two-chambered hearts are typical in fishes, enabling a single circulatory loop. The heart has an atrium that receives blood and a ventricle that pumps it to the gills for oxygenation, after which blood flows through the body and returns to the atrium. This arrangement is shared by jawless, cartilaginous, and most bony fishes, making two chambers the common heart structure among these groups. There are exceptions, such as lungfishes, which have three chambers, but the standard pattern across the broad fish line is two chambers. The other heart designs are found in other vertebrates with more complex circulations, and a lack of a heart is not applicable to fishes.