Dilian, I am not aware of any cave-obligate (i.e., troglobitic) or cave-preferring (i.e., troglophilic) bivalves in North American caves. However, some normal epigean bivalves do occur in cave streams in the U.S., and there are some cave-living gastropods here. In any case, I am very interested in seeing the information that comes from your discussion. I have listed below some cave biology publications of general interest, though none addresses molluscs.
Book Cave Life of Carter Caves State Park
Article Life Under Tennessee
Article Kentucky's hidden wildlife: Dwellers of the caves.
Article Beetles, bats, and biologists
Article Distribution of four troglophilic beetles in a Myotis sodali...
Article Terrestrial beetles (Coleoptera) of Bat Cave, Carter County, Kentucky
Article Microdistribution of scavenging flies in relation to detritu...
Hi David, Many thanks! In Bulgaria till now I found only Pisidium personatum, but some forms are strange... Stygobiotic snails are many species, in contrast, me described about 15 new species and even some new genera! Possibly the situation in the clams is not the same... After the Zhadin description of genus Speleopisidium from Caucasus, it was synonimized wth Euglesa by Korniushin (relatives of P. personatum)... As I said to my colleague and friend before: interesting is in front of us!