megacephalus is a small-to-medium-sized loricariid, reaching 12.3 cm (4.8 inches) in standard length.

megacephalus is native to South America, where it occurs in the Essequibo River basin in Guyana, as well as the Atlantic coastal drainage of Suriname.

The exact locality at which it has been found within Suriname's coastal drainage is unknown, although its presence in the region has been stated.

[3][8][9][10] In 2015, a review conducted by Jonathan W. Armbruster, David C. Werneke, and Milton Tan found the species Chaetostomus macrops (described in 1874 by Christian Frederik Lütken and also at some point placed within Hemiancistrus[11]) to be synonymous with 'P.'

Fisch-Muller, Mol, and Covain also suggested that Chaetostomus macrops may be a distinct species and not a synonym of 'P.'