Synodontis petricola ??

If you haven't read the planet catfish page I would advise doing so:

http://www.planetcatfish.com/catelog/species.php?species_id=857

And yes, they are from Lake Tanganyika.

Hmmmm...new fish...or work....tough decision

Social little buggers, whether actually petricola or the more common lucipinnis the more the merrier. If you only get a couple you'll never see them, get a half-dozen or so for better activity/visibility (unless you WANT catfish you'll never see.) Most often sold as juvies, around 1-2", they'll likely take a couple years to grow to full size.
One thing, make sure there's no gap around any HOB filters you may have. They like to swim up the outflow, and don't always make it back into the tank. I was baffled by mysteriously disappearing catfish until I found one dried out on the glass cover.

I have a 55 with a breeding pair of buescheri and about a half-dozen nearly mature juvies, a colony of multi's (at least a dozen) and 5-6 V. moorii currently about the same size as the adult male multi's. Also sharing the tank are at least 10 lucipinnis, maybe 11. I really can't remember exactly how many there are. Some are older than others, about half are large enough to spawn but still have a bit of growing to do.
I am planning on moving the Syno's into another tank for spawning sometime over the winter, but they all get along well enough in the current community.
I put a strip light on top of the 55 with the AC's to cover the openings, and didn't have any more vanishing catfish. They're in a different 55 now, filtered by a fluval canister and 2 large AC powerheads. Enclosed top w/out any escape holes.