Hmm well i got a close look at a part of the item that isnt encrusted, its impossible to get a clear picture with my camera, but underneath the shell is white. The orange material is definatly a sponge of some kind, if its boring, ill scrub it off. There are closely spaced grooves that run along the shell. Also on one part of the shell the two halves form two inward curving horn like projections. I have some oysters in my tank that hitchiked in, but i dont think that crassostrea virginica is what this is. I dont think its an oyster primarily due to its white shell, the shells thickness and the form which is hard to see under the encrustation.
Thanks for keeping on topic guys. Does anyone know of an online shell ID database for the southeast?
Ryan