In which of the following classes do fish have a 3-chambered heart?

Correct option is D

Correct Answer: (d) Dipnoi
Explanation:
→ Lungfishes (Dipnoi) possess a partially divided atrium and ventricle, functionally giving a 3-chambered heart.
→ Adaptation supports air-breathing and partial separation of oxygenated/deoxygenated blood.
→ Transitional feature between fish and amphibians.
Information Booster:
→ Dipnoi have both gills and lungs.
→ Capable of aestivation during drought.
→ Provide evolutionary clues to vertebrate land transition.
Additional Information (Other Options):
(a), (b), (c) – All typical fishes with 2-chambered hearts.