Seriously though .... are these things edible ? Let me rephrase that since having traveled extensively thanks to Uncle Sam I know people through out the world seemingly eat anything. Since these things are from Washington state do the locals eat them ? I was stationed in the Bangor Submarine base for four years near Silverdale and I never heard of these things. Clams and clam restaurants were everywhere but these critters ? 
Yes. The siphon makes a great steak; skinned, broiled, with a touch of tartar sauce, maybe smoothered in mushrooms, they are great. Because of their relative scarcity, they are a high-end dish.
Some folks think we in the Pacific Northwest are a bunch of ecological extremists, but a generation ago, in the 1960s, we could find these along public beaches. Mussels could be gathered off the pilings in downtown Seattle. Now they are farmed in a couple of very small areas.