Hermit crabs is a type of crustacean with a sift abdomen which lives its life in a shell or other protective surrounding. Hermit crabs have been a popular pet for many children and given that there are over a thousand species, the ones we know as pets are only a small proportion of hermit crabs out there in the wild as there only 15 terrestrial species.
As the hermit crab grows, it needs to upgrade its shell to a larger version. They often use the shells of sea snails and hermit crabs can fight another to gain a better shell.