New Species of Nannocharax (Characiformes: Distichodontidae) from the Northwestern Congo River Basin, with an Appraisal of Hemigrammocharax

Abstract

Nannocharax hastatus, new species, is described from the Lekoli River in the Likouala River system, Pool Malebo, and the Luilaka and Tshuapa rivers of the Momboyo river basin in the northwestern and central portions of the Congo River basin. The new species shares with N. ocellicauda and N. maculicauda a distinctive coloration pattern of a nearly completely unpigmented body other than for dark lines along the bases of the anal and dorsal fins and a longitudinally elongate, ovoid, dark spot on the posterior portion of the caudal peduncle and basal region of the central caudal-fin rays. That pigmentation pattern is unique to these three species in what was defined as the Hemigrammocharax-Nannocharax clade. In addition to coloration the three species share a distinctive overall elongate form of the head and body. Nannocharax hastatus differs from N. ocellicauda and N. maculicauda in the extent of poring along the lateral line and number of lateral line and circumpeduncular scales. Variation in the degree of poring of the lateral line in the species complex formed by these three species provides further evidence that the feature used-to-date to delimit Hemigrammocharax from Nannocharax the extent of poring along the lateral line fails to define monophyletic assemblages, and Hemigrammocharax is placed into the synonymy of Nannocharax which now forms a monophyletic assemblage.