It seems that the aspredo aspredo is the "Eel tailed banjo catfish" and the Platystacus cotylephorus is the mottled eel tailed Banjo Catfish.
The two are almost identical, and would be called colour varients of the same species, but the mottled variety has spiricles on it's tail which the other does not.
Other than that, they have the same habits and needs.
I don't care which I get!