We brought home 3 new hermit crabs a few days ago to join our family. They were all active and eager to explore their new home. The next morning, one of the new small crabs was out of it's shell, next to one of the water dishes. I immediately moved it to a separate tank by itself with food and water and several different shells for it to choose from. I separated it on Friday, and it is now Sunday morning, and it has shown no interest in returning to a shell. It moves around a little bit, and I think it has eaten a little. This morning I noticed a dark spot covering about 2/3rds of it's abdomen. Any thoughts on the prognosis?