Oxygen is absorbed into the hemolymph in the gills which provide the primary respiratory surface.

The gills hang down into the mantle cavity, the wall of which provides a secondary respiratory surface being well supplied with capillaries.

They have internal respiratory surfaces.

In many species, the parapodia, well supplied with blood vessels, act as the worm's primary respiratory surfaces.

Gas exchange is a biological process through which (usually two) different gases are transferred in opposite directions across a specialised respiratory surface.

The genus Lepeta uses the whole of the mantle cavity as a respiratory surface, while many sea butterflies respire through their general body surface.

The main respiratory surface in humans are the alveoli.

The main respiratory surface is the spongy mesophyll cells inside the leaf.

Amphibians are able to use their skin as a respiratory surface, as well as having lungs and sometimes gills.

Some is directly radiated from the skin to the air and some is lost through respiratory surfaces of the lungs.