Why do crabs store water in their gill chamber before going on land?

Crabs don't actually store water in their gill chambers before going on land. Instead, they use a special adaptation to keep their gills moist. Here's why:

* Gills need moisture: Like all fish, crabs breathe using gills. Gills need to be constantly moist to function properly.

* Land is dry: When crabs leave the water, they are exposed to the dry air. This could quickly dry out their gills and make it impossible for them to breathe.

* Branchiastegite: Crabs have a special plate called the branchiastegite that acts like a lid over their gill chamber. This plate traps a small amount of water, creating a humid micro-environment.

* Water retention: The crab's gills are covered in a thin layer of mucus, which helps to retain moisture. They also have a special structure called the "branchial chamber" that helps to circulate water over the gills.

So, in summary, crabs don't store water in their gills, they use a combination of adaptations to keep their gills moist in a dry environment.