Parotocinclus hardmani, new species, is described as a new hypoptopomatine from tributaries of the Potaro River, Essequibo River basin, Potaro-Siparuni, Guyana. The new species is distinguished from congeners in northeastern and southeastern coastal rivers of Brazil by having the canal cheek plate elongated posteriorly on the ventral surface of the head and in contact with the cleithrum. It is diagnosed from species of Parotocinclus from the Amazon, Orinoco, and Guianas watersheds by uniquely having a conspicuously elongated, conical urogenital papilla which is twice the size of the anal tube and 3–4 times larger than in congeners, by having the central abdominal area mostly devoid of plates, by mature males lacking a dermal flap on the dorsal surface of the first pelvic-fin ray, and, except for P. halbothi, by having a rudimentary adipose fin adnate to the dorsal plates, without a membrane. The new species is believed to form a clade with P. collinsae and P. halbothi, with which it shares accessory teeth on both premaxilla and dentary, the odontodes on the first pelvic-fin ray aligned with the main ray axis, not bent and pointing mesially, the lack of a triangular dark spot at the anterior base of the dorsal fin, and the lack of a Y-shaped light mark from the snout tip to each nostril.