Diamonbacked terripins will survive in a reef tank, they will eat everything in your tank, but they are salt water turtles and the young are small. They are pretty common here in New York but I think they are illegal to take. They are sometimes sold in Asian stores to eat, but I also think that is illegal so I don't know how you would get one. I used to keep them when I was a stupid kid.
http://en.wikipedia.org/wiki/Diamondback_terrapin
I know they are listed as brackish but they are fairly common here in the Long Island Sound in at least one place.I believe they are brackish, not salt.
