Why crab have gills and they can stay on land for a period of time?

Question

Why crab have gills and they can stay on land for a period of time?

Answer 1

The gills of many crustaceans are adapted to let them survive on land. Gills, like lungs, are a gas exchange organ that allows the animal to absorb oxygen and expel carbon dioxide. The oxygen does not need to be in water - as long as the gills are moist, they can absorb oxygen from the air. In crabs, the gills are enclosed in a chamber under the sides of their carapace. Crabs that live in or near water have no trouble keeping their gills moist, but crabs that spend more time on land moisten them with fluids from the body, and can seal the chambers to keep the moisture from evaporating.