For once, I think I got answer.
I got same fish 2 years ago from local store and they were marked only as Oto. Since then, one of them got so wide and almost ready to burst(obviously she was female but never get eggs from them) so I did little research and looking for few more. But I never see them until few months ago. Anyway, I think their common name is "Niger Oto". Now I have 4 of them and 1 is so wide and round. I moved to the cooler tank and keeping eyes on them like few days ago. And see if I can get any eggs.
Here is the link for it.
http/www.planetcatfish.com/catelog/speci...species_id=1386
Congrats on your great pickup. These are pretty hard to come by. I got a group of 5 oto's last year, and 4 were either Otocinclus mariae or macrospilus , and the other looked just like the one in your pic. I have battled to find out what she was, and find her some friends.
They are lovely, hard working little fish. My female eats non stop, and is a better algae eater than the other oto's.
Great pics.