LionFish says......
Ah, one of the major mistakes that happens in aggressive tanks is invert casualties. Shrimp, snails, crabs, etc. will be eaten in no time. You have to imagine that anything small, and potentially crunchy is gonna look good to an aggressive fish that has a huge appetite. Just keep in mind that most aggressive fish eat inverts in the wild and they follow their instincts in the tank too. It don't look good for the snails but it is a lesson learned. The trigger will most likely eventually rip the snails off the glass somehow and eat them. Sorry to hear it though.