Moonsnails burrow in the sand to hunt clams. If you find a clam shell on the beach with a perfect hole in it, the clam was preyed on by a moonsnail. They drill holes in the clam shells and actively cut up the flesh of the clams with their tooth-like radula. Adults will eat about one clam every 4 days.
Information referenced from Marine Life of the Pacific Northwest, by Andy Lamb and Bernard Hanby; and Shells and Shellfish, by Rick Harbo