Gill

Gills are what fish, amphibians, and some other animals use to breathe in water. They have feathery parts which cause water to move across the animal's body, which contains dissolved oxygen, after the animal has swallowed the water. The oxygen is absorbed into the animal's blood, causing carbon dioxide moves out of the animal's blood and into the water through the gills.

Gills seen on a newt (a type of amphibian)

Gills of a fish

Fish and frog gills are hidden on the sides of their heads. Sharks have many gills slits on their necks. Baby salamanders have gills that stick out like leaves from their heads.

In mushrooms, gills are the spore-bearing structure in agarics (gilled mushrooms) while fish and some young amphibians use them to get oxygen others breath.

Some insects that live in water have a plastron, which is a kind of gill. It is a patch of special hairs that keeps the water away from the insect's spiracles. This allows them to continue to take in oxygen and remove carbon dioxide while they are under water.