Branchiostegal lung

A branchiostegal lung is a special respiration organ that helps some air-breathing animals, like certain crabs and hermit crabs, breathe on land. This organ lets these creatures, such as the big coconut crab, live far from water, exploring forests and beaches.

The branchiostegal lung works by using tissue that looks like the gills these animals would have in water. But instead of taking oxygen from water like normal gills, this lung pulls oxygen from the air. Folds in the tissue give it a large surface area, helping it get as much oxygen as possible.

Not all land hermit crabs have branchiostegal lungs. Some, like those in the group Coenobita, use a mix of small gills and tiny lungs, along with other clever ways to get oxygen. This shows how different animals have found many ways to live outside of water.

Scientists think this change from water-based gills to air-based lungs happened because these animals needed ways to survive without losing too much water. Living on land means they must be careful with their water use, and these special lungs helped them do that.