May not fit in with your philosophy - but are freshwater crayfish worth looking at?
I'd read that they are good in a sump to do final cleanup of the water before it heads back to the fish tank.
I got mine on ebay and did have some in-tank reproduction before the crayfish ate them all... 'trouble is, I never knew for sure what species they were. Too bad, because they were just about the easiest thing I ever grew. :)
I spoke with the fish and game department about this extensively and it is definitely illegal in virginia to take any fresh water mussels out of the waters here. I happened to get one and was going to try to get more so I could grow them. After I found out it was illegal, I returned him to his home.