Amphibians as mediators between water and land animals

In the world of animals, some live in water and some on land. Water animals are called aquatic animals. All categories of Fish come under this category. It lives in water because they have special structures, called gills, with which they take oxygen dissolved in water. But land animals take oxygen directly from atmosphere. So they have lungs.
But amphibians have both, so can live in water and on land. As such they are termed as

Mediators between water animals and land animals.
Thanks to Pixel for providing required video clippings.