HCA: Hermit Crab Association

He's naked. I'm fairly inexperienced at owning hermit crabs. I just learned that I had the wrong kind of shells for them in the tank, so they never changed shells. We have two and one was missing for several months, shell and all. He reappeared one day about two weeks ago, but the other one was miss...

One of my crabs shed his shell and is gone. I guess that he's molting, but wasn't sure if it's usual for them to leave their shell on the surface. He's never done that before. Is this normal?