These plecos, which originate from the Rio Xingu and its tributary Rio Iriri belong to the most popular L-numbers. Now they have been described scientifically. L18, L81, L85, and L177 belong to the same species (although L81 has not been mentioned in the paper) and have been named Baryancistrus xanthellus, whereas L47 has been named Baryancistrus chrysolomus.
All these plecos become larger than 20 cm. Read more about the different varieties of Baryancistrus xanthellus here: http://www.aquariumglaser.de/en/fish-archive/l-numbers-en/_en-2/
Lexicon: Baryancistrus: ancient Greek, means “heavy Ancistrus”; Ancistrus is another genus of catfish. xanthellus: from ancient Greek, means “yellow”. chrysolomus: from ancient Greek, means “with yellow seam”.
The original scientific paper can be downloaded here: http://www.ufrgs.br/ni/vol9num2/v09n2a01.pdf
Text & photo: Frank Schäfer