I've heard of these critters before. Saw them prepared on a TV show called The Frugal Gourmet.

When the whaling ship Essex was rammed and sunk by a sperm whale, the survivors were adrift for months. While attempting to make repairs to their lifeboat they dicovered that geoducks had attached to their boat. Eating them raw sustained them for some time. Ultimately the crew resorted to canabalism.

This recount of the Essex is the basis of Herman Melville's book, Moby Dick.

Always wanted to try a geoduck. I will be in British Columbia this summer and will try to find a place that serves it.