Whee!
They are Pelusios Castaneus. Commonly, the West African Mud Turtle, or African Side Neck. I was told they're called the Gaboon Side-neck Terrapin in Germany as well, but don't quote me on that one.
That picture was taken back in August with a Fuji S1 and a 105mm macro lens. Not long before I had to send it in to get fixed actually. The upper right hand corner has some faint blue markings from the sensor that needed replacing.
Those guys are two out of five of what have been lovingly dubbed the doofus convention. My friend had what he thought at the time was 3 females in a large indoor enclosure. There were 7 (accidental) hatchlings but 2 of them went to his niece. I already have one here previously from a clutch from the Philadelphia Zoo that became my wife's favorite of all the animals, earning the coveted "tank in the kitchen" award, so once she found out we could have more (and hatchlings to boot) a new "second tank in the kitchen" award was immediately granted.
Currently all 5 live in a 40g tank. a third built out with a basking spot. I over filled it just a tiny bit as you can see from that picture since that area is supposed to be level with the waterline. They are currently about an inch to an inch and a half and all between 20 to 30 grams.
As for tank mates, amazingly enough one small comet has against all odds made it a few months now. Until they are about a year old no plant, animal or insect is safe with them in there as they are ravenous eating machines. The lucky bamboo in the background is wedged in and down into the basking platform in such a way that they just can't get it out to eat it. Not that they haven't tried. Right now, that leaf in the foreground and any of the other lower leaves have all been chewed off.
Supposedly they can get 10 to 12 inches at adult size but I've never seen one that's gotten past 8.
In the wild they are found in: Liberia, Cote D'Ivoire, Ghana, Togo, Benin, Senegal east through Guinea-Bissau, Guinea, Sierra Leone and Nigeria. Then from Gabon to northern Angola. They've also been found on Cape Verde and Sao Tome Islands.
They are omnivores and will try to eat near anything. Mine get fed: turtle pellets, koi pellets, fish (comets or minnows), snails, romaine, aquatic plants, Mazuri Tortoise diet (sometimes in the winter when plant pickings is slim), banana and sometimes other fruit. As treats they'll get chicken or turkey neck/heart/gizzard now and again.
Personality wise they are some of the friendliest aquatic turtles I've ever had. They have a very lolcat "O hai!" attitude about them when regularly exposed to people and unlike sliders (or near any other aquatic variety for that matter) they have never tried to bite or hiss at anyone holding them. Adults do however have fairly sharp front claws for digging in the muck and I have accidentally stuck myself a few times trying to give one shots.
As far as health goes except for one I took care of with a upper respiratory infection (someone dumped that one at my local petsmart) as long as they have a place they can warm up and dry out on now and again are very sturdy little guys and very easy to care for.
If you set your tank up properly, you could keep them with other fish after they get past the year or so mark. My other sub-adult is sharing a tank with a largish sun catfish and a few larger comets that grew past the eating stage and they all get along just fine. They however shouldn't be kept with anything slow moving, since if they can catch it they'll still try to eat it.
Anything else you want to know, just ask!