Ok so last night I noticed that my clam's mouth was open wide I didnt think anything of if because I had my hands in the tank scraping coraline and just cleaning things up.But when I awoke this morning I see it covered in snails.I was in shock because I had it for three years so at first I was like well i'll let the clean up crew have a good meal and pull the rest out.But as I look closer I notice the mantle still retracting like in defense. so I reached in to grab him thank god it was on the sand bed and not attached to a rock and as i look closer that it's trying to close and in the corner of the shell was one of those half shell snail wedged in there and couldn't close when the snails came in so after knocking all the snails off and the one that was inside it and fighting the clam from squeezing I finally pop off the half shell snail and it closed up.It took about ten mins but it is finally starting to open again I hope that it pulls through.