Looks like an MTS to me....
I my self not 100% sure if it is mud snail, but it looks like the picture that the OP provided.I don't think the NZ Mudsnail has spread that far (..yet), or grow that big. Could be wrong on either point though.
that does look like the one I found. hmmm...... but on the other hand, the mud snail kind of look alike too. I looked for MTS in USGS invasive species database and looks like there has been no report of MTS in Kentucky streams...... which brings me to what overstock suggested, contact local university biology department......... how exactly do you go about doing that?Here is a pic some one posted of a solid colored mts snail they had.
looks kinda like your "mystery snail".