Crab in snail shell

[Jwey]

I got a CUC today and while inspecting I found a snail moving quickly with legs. Not sure what it is so I tossed it in the mechanical side of my sump since I do t think he can climb the acrylic .

Anyone able to ID?

 

[Ranjib]

Its hermit crab. Thats how they live. Their lower body part is soft, to protect that they steal (sometime by killing) the shell of snail and then protect themselves. Normal. Keep empty shell, and dont move him out of that shell