Marvel: Amphibious Breathing

Aquaria Neptunia (Namora)
Like all Atlanteans, Namora could breathe indefinitely underwater due to having gills located behind her ears. Unlike most Atlanteans, however, Namora could also breathe on land indefinitely as well without the aid of breathing devices.

Iara Dos Santos (Shark Girl)
Shark Girl can breathe indefinitely underwater due to having gills, however she can also breathe on land indefinitely.

Namor McKenzie (Namor the Sub-Mariner)
Like all Atlanteans, Namor can breathe indefinitely underwater due to having gills located behind his ears. Unlike most Atlanteans, however, Namor can breathe on land indefinitely as well without the aid of breathing devices, whereas most Atlanteans can only survive being out of the water for a matter of minutes.