Here's the final word on the matter, afaik:
"The problem with that L-number is that DATZ and Aqualog from beginning shows 2 different species, from the first presentation in DATZ I thought that L318 was the same as L333 H. sp "New Alenquer" and I am 99,99% sure.
Aqualog has a picture of Hypancistrus sp "Monte Dourado" as L318 and this species is today L411, DATZ has a picture showing Hypancistrus sp "New Alenquer" as L318 and this species is today L401. I have an idea why it got so wrong for the "Germans", both these species was sometimes mixed from the local supplier to the exporter in Belém and from there they was often shipped as one species in the beginning. After a while when they "discovered" they was 2 species L333 H. sp "New Alenquer" and the second as L318 H. sp, some time after that the real discussion started which species they was. So L318 that was and still exports from Brazil is usual L411 and L333 "New Alenquer" is usual L401, the best thing would not to use L318 at all as L-number at least from the exporters."
It does exist, sort of, but no one will probably ever get a pair. Seidel's recent book has a pic of what is currently considered to be 318. Looks actually somewhat similar to 411, but most certainly different fish.