Astyanax fasciatus mexicanus
They look just like your average tetras you buy in pet shops. With one difference. THEY HAVE NO EYES (actually, they're born with eyes, but they shrivel up and fall off as the fish matures). They're translucent and almost transparent in some places. They live in little freshwater ponds inside caves (hence the name).
One of the coolest things about them is that they swim just like regular fish, ie, wherever they feel like it. They don't run into the sides of the fishtank at full tilt and they maneouver around obstacles in their tank fairly well. They tend to be bottom feeders since they're much better at finding things on the bottom than catching fish flakes as they float down. These suckers will literally eat anything, which my girlfriend found out the hard way when her Placo disappeared. They're not agressive fish; they just seem to have trouble telling the difference between food and fish fins/other fish.
Cave tetras are schooling fish, so if you get any you should probably have at least 3. Any long fins in the tank are likely to get nipped for the reason listed above. They'll eat fish flakes as normal. They're freshwater fish and can take a wide variety of tank temperatures (my girlfriend's cave tetras seemed just fine in 74 degrees Farenheit water). They're quite cool little fish.