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[[ Cnesterodon Garman ZBK ]]
Cnesterodon Garman, 1895 ZBK is a well-diagnosed, monophyletic genus of poeciliid fishes whose nomenclature, taxonomic history, and phylogenetic relationships were discussed in detail by Lucinda & Reis (2005) and Lucinda (2005), respectively. Fishes of the genus Cnesterodon ZBK are small poeciliids, diagnosable by the possession of the following uniquely derived and unreversed features: (1) anterior tip of basipterygium sinuous in adult males; (2) outer surface of basipterygium base narrow in adult males; (3) haemal arch and spine of vertebrae 13-17 in adult males modified in rudimentary gonapophyses; (4) gonapophysis of vertebra 14 rudimentary in adult males; (5) distal portion of pleural ribs 6, 7, and 8 in adult males expanded; (6) large bony basal process on first anal-fin proximal radial in adult males; (7) unpaired appendix at tip of anal-fin ray 3 (R3); (8) distal segment at tip of anterior ramus of anal-fin ray 5 (R5a) transformed into a retrorse triangular spine; (9) dark brown spot posterior to anal-fin base of males continuous ventrally side by side and meeting ventral median line of caudal peduncle (Lucinda, 2005). Lucinda & Reis (2005) recognized the clade Phalloceros Eigenmann, 1907 ZBK + Phallotorynus Henn, 1916 ZBK as the sister-group of Cnesterodon ZBK , which together comprise the tribe Cnesterodontini. Despite the well-corroborated monophyletic diagnosis and phylogenetic position of the genus Cnesterodon ZBK , its intrageneric relationships, intrageneric diversity, and species distribution patterns are not well understood.
Cnesterodon ZBK comprises nine recognized valid species inhabiting coastal and inland drainages of Argentina, southern Brazil, Paraguay, and Uruguay, with most of the known species restricted to the headwaters or upper portions of the river systems throughout their range (Lucinda, 2003; 2005). The first described Cnesterodon ZBK species is the generic type, C. decemmaculatus (Jenyns, 1842) . A second species, C. carnegiei Haseman, 1911 ZBK , was described 69 years later. A gap of 82 years separates the description of C. carnegiei ZBK from the first taxonomic revision of Cnesterodon ZBK by Rosa & Costa (1993). The number of species of Cnesterodon ZBK has grown significantly in little more than a decade, with four species recognized in Rosa & Costa’s (1993) revision, and increasing to nine by the time Lucinda’s (2005) study appeared. The most recent species described include C. hypselurus Lucinda & Garavello, 2001 ZBK ; C. omorgmatos Lucinda & Garavello, 2001 ZBK ; C. raddai Meyer & Etzel, 2001 ZBK ; and C. iguape Lucinda, 2005 ZBK ; with another new species currently being described by Anza, Lucinda & Malabarba (referred to as Cnesterodon sp. n. B in Lucinda, 2005, Lucinda & Reis, 2005, and herein). Recent collections in the río Uruguay basin in the department of Artigas, northern Uruguay (Fig. 1) have revealed yet another new species of Cnesterodon ZBK , which is described herein.