A new Scleromystax species (Siluriformes: Callichthyidae) from coastal rivers of southern Brazil

Abstract

The recently resurrected callichthyid catfish genus Scleromystax includes species occurring in several Brazilian coastal river basins from southern Bahia to southern Santa Catarina. Several character states, especially those related to sexual dimorphism, demonstrate the monophyly of Scleromystax. Examination of Scleromystax specimens sampled from streams in the Ilha de Santa Catarina and Nova Veneza, and the rio Mampituba basin, Santa Catarina and Rio Grande do Sul States, revealed that they constitute a new taxon, and thus the southernmost record for the genus. Scleromystax salmacis, new species, has coloration similar to that of S. macropterus, differing from that species mainly by the absence of a black spot on the base of the median caudal-fin rays, and transverse blotches along the body more irregular than those in S. macropterus. In addition to differences in coloration and external and osteological characters, the new species differs from S. barbatus and S. prionotos by its more rounded snout. The new taxon is also distinguished from its congeners by the presence of a single perforated dorsolateral body plate, similar to the condition found in some Aspidoras species, orientation of the ventral keel of the scapulocoracoid, and by the absence of sexually dimorphic features.O gênero Scleromystax foi recentemente revalidado e inclui espécies distribuídas nas diversas bacias hidrográficas costeiras entre o sul do Estado da Bahia e o sul do Estado de Santa Catarina. O monofiletismo de Scleromystax é demonstrado por vários estados de caráter, sendo aqueles relacionados ao dimorfismo sexual os mais evidentes. O exame de exemplares de Scleromystax coletados em rios da Ilha de Santa Catarina e do município de Nova Veneza, e da bacia do rio Mampituba, Estados de Santa Catarina e Rio Grande do Sul, revelou que os mesmos representam uma nova espécie, sendo este o registro mais austral do gênero. Scleromystax salmacis, espécie nova, apresenta o colorido semelhante a S. macropterus, porém difere desta principalmente pela ausência de uma mancha arredondada e escura na base dos raios medianos da nadadeira caudal, e pelas manchas transversais ao longo do corpo serem mais irregulares que em S. macropterus. Além do colorido e de caracteres de morfologia externa e osteológicos, a nova espécie distingue-se de S. barbatus e S. prionotos pela forma mais arredondada do focinho. O novo táxon distingue-se de todos os seus congêneres pela presença de somente uma placa dorsolateral com poro da linha lateral, semelhante ao estado observado em algumas espécies de Aspidoras, orientação da quilha ventral do escápulo-coracóide, e pela ausência de caracteres relacionados ao dimorfismo sexual.

New species of Scleromystax Günther, 1864 (Siluriformes: Callichthyidae) - extending the meridional distribution of genera endemic to the Atlantic Forest

“…That species was described from the rio Mampituba and rio Araranguá, in Santa Catarina State (Britto & Reis, 2005) based on a few lots. These two rivers form, along with the rio Tramandaí drainage, an area of endemism in southern Brazil, sharing a number of endemic fish species (Malabarba & Isaia, 1992;Reis & Schaefer, 1998;Hirschmann et al, 2015), and historically united in a single palaeodrainage in the area exposed with the retreat in sea level during the Last Glacial Maximum .…”

“…Morphometric and meristic data were taken following Reis (1997) and Britto & Reis (2005). Measurements were obtained with calipers to 0.1 mm.…”

“…The most useful characteristics are the elongate pectoral and dorsal fins, and the sides of snout (cheek region) bearing pointed, relatively long odontodes embedded in fleshy papillae. Notwithstanding, those features show a variable degree of development within the genus (Britto & Reis, 2005: 486-487), and S. salmacis displays none of the dimorphic conditions in addition to the shape of the genital papillae (Britto & Reis, 2005: figs. 1-2).…”

“…The new taxon could be easily assigned to Scleromystax, displaying the character-states that defines the genus, such as a slender palatine, an elongate lateral ethmoid (Britto, 2003), presence of minute odontode-bearing platelets between posterior tip of parieto-supraoccipital and nuchal plate, and posterior process of parieto-supraoccipital and nuchal plate both elongate, almost reaching, but not touching each other (Britto, 2003;Britto & Reis, 2005). Besides, S. reisi presents the sexually dimorphic conditions found in almost all Scleromystax representatives, although in a less-conspicuous form.…”

“…These records includes the description of a new species of Scleromystax from the rio Mampituba drainage (Britto & Reis, 2005), a new Hollandichthys from the rio Maquiné, rio Tramandaí drainage , and a new Listrura from the laguna dos Patos drainage (Villa-Verde et al, 2013). In all these cases, these peripheral populations seems to be small and hardly represented in collections, when compared to the species of those genera found in the central areas of the Atlantic forest.…”