Hidden in plain view: A new Labeo (Cyprinidae: Labeoninae) endemic to the Kouilou-Niari River basin in the Lower Guinea ichthyological province.

Labeo niariensis sp. nov., a small-sized Labeo species, is described from the Kouilou-Niari River system in the Lower Guinean ichthyofaunal province. The species is a member of the newly erected Labeo annectens species group. Morphologically, it is distinguished from all congeners by the presence of a deeply bifurcate posterior process of the kinethmoid. It further differs from all the described Lower Guinean Labeo, except L. annectens and Labeo nunensis, by possessing six (vs. five or fewer) pre-dorsal vertebrae. The new species is further distinguished from L. annectens and L. nunensis by the presence of a prominent anterior notch and moderately developed posterior process on the first infraorbital (lachrymal) versus absence of an anterior notch and an elongated posterior process, presence of a deeply ovoid second infraorbital versus narrow and elongate, and by meristic and morphometric differences in body shape and proportions. L. niariensis is currently only known from the Kouilou-Niari River system in the Republic of Congo.