Editorial Type:
Article Category: Research Article
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Online Publication Date: May 01, 2000

On Sternarchorhynchus Castelnau: A South American Electric Knifefish, with Descriptions of Two New Species (Ostariophysi: Gymnotiformes: Apteronotidae)

Page Range: 521 – 535
DOI: 10.1643/0045-8511(2000)000[0521:OSCASA]2.0.CO;2
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Abstract

This paper summarizes information on the South American freshwater gymnotiform genus Sternarchorhynchus Castelnau (family Apteronotidae), especially taxonomic and systematic. Sternarchorhynchus britskii and S. mesensis are described as new from the upper portions of the Rio Paraná and Rio Tocantins (Brazil), respectively. The new species are distinguished from currently recognized species by morphometric and meristic features such as the relative sizes of structures in head, size of pectoral fin, and number of anterior unbranched anal fin rays. The two new species, along with S. curvirostris (Boulenger) and S. roseni Mago-Leccia, are hypothesized to comprise a monophyletic subunit, tentatively recognized herein as the “Sternarchorhynchus curvirostris group,” based on the color pattern of anal and pectoral fins. Species relationships within Sternarchorhynchus are discussed.

Este trabalho resume informações sobre o gênero sul-americano de Gymnotiformes Sternarchorhynchus Castelnau (família Apteronotidae), especialmente taxonômicas e sistemáticas. Sternarchorhynchus britskii e S. mesensis são descritas como novas das porções superiores dos rios Paraná e Tocantins (Brasil), respectivamente. As novas espécies são separadas das demais espécies válidas atualmente incluídas no gênero com base em características morfométricas e merísticas tais como, por exemplo, o tamanho relativo de estruturas na cabeça, nadadeira peitoral e número de raios anteriores indivisos da nadadeira anal. Estas duas novas espécies, juntamente com S. curvirostris (Boulenger) e S. roseni Mago-Leccia, são supostas como compreendendo uma subunidade monofilética reconhecida aqui de maneira tentativa como o “grupo Sternarchorhynchus curvirostris” com base em padrões de coloração das nadadeiras anal e peitoral. Relações entre as espécies de Sternarchorhynchus são discutidas.

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Copyright: The American Society of Ichthyologists and Herpetologists
Fig. 1.
Fig. 1.

Head and anterior portion of body of Sternarchorhynchus oxyrhynchus (holotype of Sternarchus oxyrhynchus), ZMB 4086 (470.0 mm TL, 394.0 mm LEA). Essequibo River, Guyana

Fig. 2.
Fig. 2.

Head and anterior portion of body of Sternarchorhycnhus mormyrus (syntype of Sternarchus mormyrus), NMW 65336 (regenerated tail, approximately 370.0 mm LEA). Marabitanos, upper Rio Negro, Amazonas, Brazil

Fig. 3.
Fig. 3.

Sternarchorhynchus curvirostris (syntype of Sternarchus curvirostris), BMNH 1880.12.8:90–91 (203.0 mm TL, 188.0 mm LEA). Canelos, Río Pastaza system, Ecuador

Fig. 4.
Fig. 4.

Head and anterior portion of body of Sternarchorhynchus roseni, INPA 4817 (regenerated tail, approximately 340.0 mm LEA). Rio Amazonas, Paraná do Rei, Ilha do Careiro, Amazonas, Brazil. Note light narrow band on frontal portion of head and snout and conspicuous distal dark margins on anal and pectoral fins

Fig. 5.
Fig. 5.

Distribution of Sternarchorhynchus in South America represented by type localities of species so far described in the genus. Star = S. oxyrhynchus; asterisk = S. mormyrus; diamond = S. curvirostris; circle = S. roseni; square = S. britskii, sp. nov.; and triangle = S. mesensis, sp. nov. See text

Fig. 6.
Fig. 6.

Skull of Sternarchorhynchus mesensis, sp. nov., MNRJ 11611 (paratype; lateral view, left side). ANG = anguloarticular; BOC = basioccipital; DNT = dentary; EPO = epioccipital; ESF = sphenotic; ESP = sphenotic spine; EXO = exoccipital; FRO = frontal; HIO = hiomadibula; IOP = interopercular; MAX = maxilla; MES = mesthmoid; MET = metapterygoid; OPE = opercle; ORS =orbitosphenoid; PAR = parietal; PAS = parasphenoid; PMX = premaxilla; POP = preopercular; PRO = prootic; PTO = pterotic; PTS = pterosphenoid; QUA = quadrate; RAR = retroarticular; RBR = branchiostegal rays (only four depicted, one hidden); SIM = symplectic; SOC = supraoccipital; SOP = suboperculum; and VOM = vomer

Fig. 8.
Fig. 8.

Tree summarizing generic level phylogenetic relationships within the family Apteronotidae (clade A) and an included tentative hypothesis to Sternarchorhynchus species (Albert and Campos-da-Paz, 1998; Campos-da-Paz, 1999). Sternarchorhynchinae = clade B; Sternarchorhynchus = clade D; the “Sternarchorhynchus curvirostris group” = clade E. Clades C and F unnamed. See text for discussions of supporting synapomorphies

Fig. 9.
Fig. 9.

Head and anterior portion of body of Sternarchorhynchus britskii, sp. nov., MZUSP 52923 (holotype; 261.0 mm TL, 243.0 mm LEA). Rio Paraná at Ilha Solteira dam (coffer-dam, right margin), Mato Grosso do Sul, Brazil

Fig. 10.
Fig. 10.

Head and anterior portion of body of Sternarchorhynchus mesensis, sp. nov., MNRJ 17591 (holotype; 249.0 mm TL, 226.0 mm LEA); Rio Tocantins (upper Rio Tocantins region), at Serra da Mesa dam (coffer-dam), municípios Minaçu/Uruaçu (“Minaçu/Cavalcante”), Goiás, Brazil

Fig. 7.
Fig. 7.

Endopterygoid (MPT), and quadrate (QUA) of Sternarchorhynchus mesensis, sp. nov., MNRJ 11611 (paratype; lateral view, left side)

Accepted: Oct 08, 1999