A hermit crab may live in the water or on the land.
They do not have a hard covering over their body like other crabs. Only their legs are protected by a hard covering. They find shelter in a shell. It has to hang onto the inside of the shell so it does not fall off.
As they grow too big for their shell they search to find a larger one to live in.
They spend a lot of time searching for just the right shell.
Hermit crabs also moult - they shed their skin as they grow.