IMO it sounds like a case of PPS. I have posted the link below;
http://www.hermitcrabassociation.com/ph ... 67&t=92531
I have had several pet shop crabs go through this and have done exactly what you are describing. I wish I could say they made it, but they didn't. Sorry you are dealing with this. It can be very hard.
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He is adorable BTW! It is an uneasy felling when they shift in the shells, I know exactly what you are talking about. I would just let him be and if he is passed, you will smell rotten fish, its really an unmistakable smell. Unfortunately, these crabs go through so much before they end up in our tanks, and sometimes its just too much for them. Don't be discouraged though. PPS is unavoidable, all you can do is just have the proper conditions and hope for the best. It is important to have a day/night cycle for the crabs as they are getting acclimated to their new home. Hopefully your little buddy beats the odds and pulls through for you!
Also, below is our help template. If you can fill that out, we can make sure everything is set up correctly!
What kind of substrate is used in your tank and how deep is it?
2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
3. Is a heat source used in the tank? If so, what?
4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
5. What kinds of food do you feed and how often is it replaced?
6. How long have you had the crab and what species is it, if known?
7. Has your crab molted, and how long ago did it happen?
8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
9. How many crabs are in the tank and about how large are they?
10. How many extra shells are usually kept in the tank, if any?
11. Have there been any fumes or chemicals near the crabitat recently?
12. How often do you clean the tank and how?
13. Are sponges used in the water dish? If so, how are they cleaned?
14. Has anything new been added to your crabitat recently?
15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?
16. Please describe the emergency situation in detail.