I have heard of people having crabs before, but usually they are trying to get rid of them.
I never really thought of keeping a hermit crab as a pet, so I guess I had no idea there was a need for a Hermit Crab Pool. In this case, not only do you get such a gadget for them to maintain moisture, but it looks like a mini lifesaving ring. For their amusement, I guess.
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