Out here, clams are probably their #1 source of food. Some of the flats are littered with smashed clam shells, but i have not found a pattern that works yet. The big issue is the "plop" factor. you have to still fish the clam, so you really need a pattern that you can drop right on the fish. Trying to lead a carp with a pattern you can't strip or move is a challenge, and if you strip a clam, they spook. So far, everything I've tried has been too heavy and made too much noise entering the water, or too light and i can't get it on the fish before they are moving off to another spot. i've caught exactly 1 carp on a clam pattern!
That said, i think the carp take the worm for the extended foot of a clam. When the clams feed, they extend their foot out a bit and syphon food from the water. I think the carp often eat the worm, thinking it is a feeding clam (with the body/shell buried). when they take a worm, they almost always burrow down into the bottom a bit to eat it.