Marcusenius elegans: a replacement name for Marcusenius gracilis Kramer 2013 (Osteoglossiformes: Mormyridae), a secondary junior homonym of Marcusenius senegalensis gracilis (Pellegrin 1922)

The West African mormyrid Marcusenius gracilis Kramer 2013 is a secondary homonym of Gnathonemus gracilis Pellegrin 1922 when both species are placed in the same genus Marcusenius (International Code of Zoological Nomenclature, article 57.3). Marcusenius gracilis was first described by Kramer (2013: 123), based on a holotype and 16 paratypes from Ivory Coast, West Africa. The taxon was subsequently treated as a valid species of Marcusenius by Kramer & Wink (2013: 2334), and by Fricke et al. (2022). Kramer (2013) was not aware of Gnathonemus gracilis Pellegrin 1922, which was originally described by Pellegrin (1922: 221), based on a specimen from the Gribingui River, Lake Chad basin, in today’s Central African Republic. The holotype is extant (MNHN 1922-0023). The taxon was treated as a synonym of the West African species Marcusenius senegalensis (Steindachner 1870), but as a valid subspecies (Gosse 1984: 89, Lévêque et al. 1991: 138). Marcusenius senegalensis gracilis (Pellegrin 1922) has precedence over Marcusenius gracilis Kramer 2013, and the latter must be renamed when both taxa are classified in genus Marcusenius. Marcusenius elegans nom. nov. is herein proposed as the replacement name for Marcusenius gracilis Kramer 2013. The new species epithet is based on the Latin word elegans, meaning elegant, referring to its slender body; the name is treated as an adjective.