gasp! tragedy! the Aqualog has almost nothing to say! (beautiful pictures tho')
i think that all three of these species are sedentary, biters, hiders, and freshwater. tugidus & leiurus get to be ~15 cm. cochinchinensis gets about ~7 cm. the first two need larger tanks between 50 and 75, and the latter needs between 30 and 50 gallons.
put some pictures up and maybe someone can narrow the id. otherwise, *shrug* get a 40 or 50 and keep it by itself. there's not too much difference beyond the sizes, so the precise id isn't that necessary.