From what I can find, they're an extremely sensitive rheophilic sisorid that is not very easy to collect in any large quantities and is extremely difficult to keep alive during the shipping process, and in the home aquaria for the matter, due to their extreme activity and tendency to put on random bursts of speed, inevitably crashing into surfaces in the restriction of a tank without significant flow. The Nangra in the second image is in poor condition, and seems to be suffering from a number of ailments; I do not expect it to have lived long after the image was taken.