Abstract
ABSTRACT Schizodon dissimilis is redescribed on the basis of syntypes and non-type specimens from the Parnaíba, Jaguaribe and Mearim rivers, and lectotype and paralectotypes are designated. Schizodon dissimilis is distinct from the Amazonian and southeastern Brazil congeners by having four dark brown vertical bars without a midlateral dark brown stripe or a dark blotch on caudal peduncle. When compared with the northeastern Brazilian Schizodon and those from the São Francisco river, and with the remaining dark barred species S. australis, S. borellii, S. corti, S. fasciatus and S. intermedius, it is diagnosed by a combination of lateral line scale counts, color pattern and body proportions. The color pattern distinguishes S. dissimilis from S. fasciatus and the meristic and morphometric data are important in separating S. dissimilis from S. intermedius and S. borellii. Schizodon dissimilis and S. fasciatus have disjunct distributions, with the first occurring in northeastern basins, and the second widely distributed through the Amazon basin and rivers draining northward from the Guyana Shield. Schizodon intermedius and S. borellii are respectively native to the upper Paraná and Paraguay river basins while S. australis is known from the Paraná-Uruguay system and S. corti was described from Maracaibo, Venezuela.
Highlights
The anostomid genus Schizodon was created by Agassiz for the species S. fasciatus described by Spix, Agassiz (1829) from Brazilian rivers
We evaluate the members of Schizodon fasciatus species group and redescribe Schizodon dissimilis (Garman, 1890) based on examination of the syntypes of this species from the rio Poti and additional specimens from the rivers Parnaíba, Poti, Jaguaribe and Mearim
PC2 alone failed to discriminate between the four species analyzed (S. borellii, S. dissimilis, S. fasciatus, S. intermedius); a scatterplot of the sheared PC2 and sheared PC3 (Fig. 1) separated S. intermedius from the other three species, and separated S. dissimilis from S. intermedius and S. borellii
Summary
The anostomid genus Schizodon was created by Agassiz for the species S. fasciatus described by Spix, Agassiz (1829) from Brazilian rivers. In his revision of anostomid fishes, Myers (1950) recognized Schizodon as a genus with eight serrate teeth on each jaw. That dental character remained the diagnostic feature for Schizodon until recently, when Sidlauskas, Vari (2008) added that the second and third teeth of premaxilla have four cusps, and the distal margin of the main lobe of the symphyseal dentary tooth has three distinct cusps Those authors proposed two osteological synapomorphies for Schizodon, the wide ascending process of the anguloarticular and a torsion in the medial flange of the mesocoracoid. Schizodon currently comprises fifteen species: S. fasciatus Spix, Agassiz, 1829, S. vittatus (Valenciennes, 1850), S. isognathus Kner, 1858, S. nasutus Kner, 1858, S. knerii (Steindachner, 1875), S. dissimilis (Garman, 1890), S. platae (Garman, 1890), S. borellii (Boulenger, 1900), S. rostratus (Borodin, 1931), S. corti Schultz, 1944, e180035[1]
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