Review of the southern African slender stonebashers, genus Heteromormyrus Steindachner 1866 (Teleostei: Mormyridae), with description of six new species.

Recent molecular studies have advanced our knowledge of the taxonomic diversity and generic placement of the slender stonebashers, previously placed in the genus Hippopotamyrus, in southern Africa. These fishes were recently transferred to the genus Heteromormyrus whose range encompasses the Kwanza, Kunene, Okavango, Zambezi, Pungwe and Buzi River systems in southern Africa, as well as the southern tributaries of the Congo River system. The present study builds on previous research that identified at least eight candidate species within the Heteromormyrus ansorgii species complex by providing formal descriptions for six new species and redescriptions of Heteromormyrus pauciradiatus and H. ansorgii s.s. The Kwanza River system is peculiar because it currently has five known species in this genus, some of which are co-distributed, whereas the other river systems have only one or two species in this genus. Two of the new species, Heteromormyrus dolichorhynchus sp. nov. and Heteromormyrus angusticaudata sp. nov., are endemic to the Kwanza River system. Heteromormyrus xanekweorum sp. nov. is confined to the Okavango River system, Heteromormyrus chilembwei sp. nov. occurs in the Ruo River (lower Zambezi River system), Heteromormyrus tangwenai sp. nov. is endemic to the Pungwe River system and Heteromormyrus ndauorum sp. nov. is endemic to the Buzi River system. Species in this genus exhibit high morphological similarity, but they can be separated by a combination of characters, including scale counts, dorsal- and anal-fin ray counts, vertebral counts, caudal peduncle depth, position of nostrils, head shape and variation in colour pattern. Taxonomic diversity within this genus is likely to be higher than currently known, and future studies, particularly in the Kwanza and upper Zambezi rivers, are anticipated to uncover additional new species.