I have no clue what this turtle is - I have sliders!

Question
I got this little guy from a petstore a few days ago that had no clue what he was either. I bought him/her because I felt sorry for him - he was in a tank with a bunch of RES and MAP turtle Hatchlings as well as a few Painted turtle Hatchlings but he just looked completely different. I actually put my hand in the tank to rescue another turtle that had gotten stuck and came out with this little guy and thought he was so ugly he was cute. I have him in my 50 gallon tank with my 4 RES that range from 1 year old to 4 mos. and they seem to be getting along well. He is all black with a reddish orange belly and a rather domed shell. and very tiny. I would say less than a half inch and very thin. He/she looks like a BEETLE! Here is link to two pictures of him.
http://s213.photobucket.com/albums/cc30/TheMuseTrap/


Answer
It looks like a Common Musk Turtle- http://www.austinsturtlepage.com/world_of_turtles/Stinkpots_(Common_Musk_Turtles)_-_Sternotherus_odoratus/index.html

These are small turtles that are considered good pets. Here is a link- http://www.austinsturtlepage.com/Care/caresheet-stinkpot.htm