Derasa Clam and Nassarius Snails

[russeko8]

Any body ever have promblems with Clams and nassaruius snails. It seems every month roughly my nassarius snails seem to get all over my big derasa clam like it is dinner. They never bother any of my other clams one maxima and one crocea. I take the clam out of the tank to my frag tank for a day or two it is fine put it back in the tank and a month or so later same thing. When I pull the clam out the snails have there tubes stuck inside of the clam. After removing it from the situation it seems fine and goes about its buisiness. I do keep him on the sand bed but with a rock under the sand. Maybe when I put him back I will put him on a rock off the sand. My other clams are on the sand with a rock under them with no issues, and the weird thing is the time span seems to be the same all the time from when he goes back to when this happens about a month?