Review of the South American cichlid genus Mesonauta Günther (Teleostei, Cichlidae) with descriptions of two new species

Five species of Mesonauta are diagnosed and described. Two of them are new. Mesonauta insignis (Heckel), in the upper Rio Negro and Rio Orinoco, is characterized especially by slender shape and by having a single wide dark bar above the abdomen instead of two. Mesonauta f e stivus (Heckel), in the Paraguay and Bolivian Amazon basins, Rio Jamari and lower Rio Tapajs, is the most deep bodied Mesonauta species and has microbranchiospines on all four gill arches but rarely preopercular scales; the Rio Tapajs population can be distinguished by being more slender and by averaging higher anal spine count and lower abdominal vertebral count than more southern M. f e stivus. Mesonauta acora (Castelnau), in the Tocantins and Xingu drainages, has scales on the preopercle, microbranchiospines on all gill arches and a distinctive mottled colour pattern. Mesonauta egre gius n. sp., in the Colombian Orinoco basin, has the vertical dark bar above the anal fin origin divided, but it has no horizontal striping and also features characteristic low meristics, such as 13+13 vertebrae instead of 12+14 or 13+14, and usually A. VII. 11 which is lower than in the other species. Mesonauta mirificus n. sp., in Peruvian Amazonia, has the dark vertical bar above the anal fin origin divided into two and presents thin dark stripes along the sides. Additional species of Mesonauta exist, but shortage of suitable material prevents formal descriptions.