Lungs vs. Gills: No Known Animal Uses Both for Respiration

There are no extant animals that simultaneously use both lungs and gills as functional respiratory organs.

• Lungs – Air‑breathing; evolved in tetrapods and some fish (lungfish, bichirs).
• Gills – Water‑breathing; typical of fish, amphibian larvae, many invertebrates.

Transitional Forms

• Lungfish – Have both gills and a lung; aestivate in mud using lung, but gills are reduced/non‑functional in air.
• Amphibians – Larval gills → metamorphosis → lungs + cutaneous respiration; not simultaneous functional gills + lungs.
• Some crabs/mollusks – Have both gill‑like and lung‑like structures but use one medium at a time.

True bimodal respiration (simultaneous efficient gas exchange in both air and water) does not exist in vertebrates.