Marvel: Amphibious Physiological Adaptation

Aquaria Neptunia (Namora)
Namora's body was specially developed for underwater conditions, granting her specialized blood circulation to withstand freezing temperatures and highly-developed vision to see clearly, even in murky ocean depths. This hybrid physiology meant she could survive indefinitely underwater or on land, though she would need occasional contact with water to survive.

Iara Dos Santos (Shark Girl)
This hybrid physiology means she can survive indefinitely underwater or on land. Although, like sharks, if she tastes blood, she goes into a frenzy for a time.

Namor McKenzie (Namor the Sub-Mariner)
Namor's body is specially developed for underwater conditions, granting him specialized blood circulation to withstand freezing temperatures and highly-developed vision to see clearly, even in murky ocean depths. This hybrid physiology means he can survive indefinitely underwater or on land, though he would still need occasional contact with water to survive.