help with pyramid snails

[hillegom]

I could not believe it. I have had my clam for about 8 months. When I first received it I checked for the snails and saw none.
Last week, I saw one, so took the clam out and found about a dozen and egg masses. Got rid of them by brushing them off and washing.
So 2 days ago the clam is not opening fully, so took it out and found 3 small snails. The clam still does not fully open.
I thought I read somewhere, where the snails could go inside the clam and eat it from the inside out. Is this true?
Any other ideas?
Thanks