Shells with holes - ID both shell and animal that made them

[bellzeybubba]

Hello, I'm hoping you folks can help me find the resources I need.

My son (2nd grade) wants to do a Science Fair project about some of the sea shells he collected this summer in Myrtle Beach, South Carolina, USA.  What interested him the most was that some shells were full of holes, for his project he wants to do a presentation of how the shell is formed and how the holes are made.

He picked the shells that had the most holes in them, so none of them are complete.  I'm pretty sure the dark ones are oyster shells and I think the other ones could be clams (white/grey bands, fairly large, thick pieces), how could I confirm or at least get a rough identification?  Most guides I've seen online are for intact shells (of course) but none seem to include oysters.

Also from searching around online we know that the holes are called by bioerosion from sea animals like boring sponges, but I haven't found anything that will help us identify which animal from the look of the holes.  Any ideas where to look?  If we can't find it he'll just do a general presentation about bioeroders, but if we can do it he'd love to have each of his specimens identified.

Thanks for any help <img src="images/smiley/smile.gif" alt="" border="0" />