dissapearing snails

[Richard_Dicosimo]

i have had my tank for 4 months now. i have 3 cleaner shrimp, 1 coral branded shrimp, and an army of snails. my army of snails has slowly been dissapearing, i dont think that this is a mantis shrimp because none of the shells are cracked just empty, and my shrimps are still alive. maybe im wrong in thinking that mantis shrimps crack snail shells to extract the snail, but does anyone have an idea of whats going on?

i did once see one of my cleaner shrimps eating a dead snail but i figured it was just old age that killed that snail. maybe i have evil cleaner shrimp.