well havin' crabs is never a thing to carry on about.......
...but in regard to your emeralds......it is very possible that the dead speciman was the remians of a molt....they shed the entire skeleton as they grow and the remains will often look exactly like a dead emerald. Normally they'll hide away for a few days after molting so I'd keep a eye out for him.......
...and sorry about the cheap "crab" joke.....I couldn't resist....its early and the meds I'm on affect me.