It appears Hypancistrus margaritatus is the formal name given to a pleco aquarists have previously identified as L404, an uncommonly traded species. It is also rare in nature; the researchers state: “ Hypancistrus margaritatus appears to be rare, as only one specimen was collected during four expeditions that yielded 55,156 fish specimens.”
As with other Hypancistrus sp., this is a relatively small pleco (albeit large for the genus) with an adult size in the four to five inch (10-12cm) range.
The ZooKeys paper also describes another new pleco species, Hypancistrus phantasma, collected from the same relative area. No live photo exists of this species. In fact, the single collected specimen is the only known example of this species, hence it’s etymology (“the phantom”).