I have a small reef tank and I introduced an emerald crab to live with my Royal Dottyback and pair of Common Clowns a few months ago. All went well after Dotty calmed down and Mr. Crab seemed happy, doing a great cleanup job around the tank. Yesterday, I found him floating around, lifeless, without legs - and his shell looking somewhat smaller than I remember.
Pic attached before I laid poor Mr. Crab to rest in the back garden. I miss him.
Can anybody hazard a guess as to what might have caused this?