Revision of The Deep-channel Electric Fish Genus Sternarchogiton (Gymnotiformes: Apteronotidae)

The Neotropical ghost knifefish genus Sternarchogiton is revised on the basis of morphology and pigmentation. A new diagnosis for the genus is provided. Two new deep-channel taxa from the lowland portions of the Amazon basin are described: S. labiatus and S. preto. Sternarchogiton labiatus is diagnosed by the possession of a hard, prominent, three-lobed structure on the lower lips, two rows of teeth on the dentary, a second hypobranchial with a medial bridge, an ossified first basibranchial, and cartilaginous posterior basibranchials. Sternarchogiton preto is diagnosed by black or very dark brown body coloration, five long and conical teeth on the premaxilla, a dentary with one row of conical teeth pointing toward inside of mouth, the fusion of the supracleithrum and posttemporal, and anterior portion of coracoid not reaching anterior edge of cleithrum. A dichotomous key to species of the genus is provided.

Resumen

Os peixes-faca Neotropicais Sternarchogiton são revisados com base na morfologia e pigmentação. Uma nova diagnose para o gênero é fornecida. Duas espécies novas de canais profundos da bacia Amazônica são descritas: S. labiatus e S. preto. Sternarchogiton labiatus é diagnósticado pela presença de uma estrutura dura, proeminente e tri-lobada, sobre o lábio inferior, um segundo hipobranquial com uma ponte medial, o primeiro basibranquial ossificado, e os basibranquiais posteriores cartilaginosos. Sternarchogiton preto é diagnósticado pela presença de uma coloração preta no corpo, cinco dentes grandes e cônicos sobre o pré-maxilar, um dentário com uma fileira de dentes cônicos, orientados para dentro da boca, fusão do supracleitro e o pós-temporal, e a porção anterior do coracóide não alcançando a borda anterior do cleitro. Uma chave dicotômica é fornecida para as espécies do gênero.

Figure 1

Photographs of Sternarchogiton nattereri, showing striking secondary sexual dimorphism of external cranial morphology. (A) Preserved male, INPA 15799. Note anteriorly elongated head and crowns of external maxillary and dentary teeth. (B) Live male, MCP 38308, also exhibiting elongated head and partially developed external teeth crowns. (C) Head and (D) entire live female, MCP 38307, exhibiting external cranial morphology typical of female and immature specimens. Scale bars = 10 mm.

Figure 2

Electric Organ Discharge (EOD) waveform (left) and Fourier Power Spectrum (right) of (A) Sternarchogiton nattereri, MCP 38306 (female); (B) Sternarchogiton preto, MCP 37555 (male); (C) Sternarchogiton labiatus, UF 147994 (male). Waveforms are plotted with head-positive upwards, time on abscissa (scale bar = 1 ms) and voltage on ordinate. Power spectra were computed by 65536 point Fast Fourier Transform from 3 s digital recordings (sample rate = 96 kSs). Abscissa represents frequency (kHz) and ordinate amplitude (dB), with Peak Power Frequency scaled to 0 dB.

Figure 3

Map of northeastern South America showing distribution of Sternarchogiton nattereri (squares, 1 = type locality); Sternarchogiton porcinum (triangles, 2 = type locality); Sternarchogiton preto (stars, 3 = type locality); and Sternarchogiton labiatus (circles, 4 = type locality, 5 = locality reported by Cox-Fernandes, 1995:figs. 2–41). Some symbols represent more than one lot or locality.

Figure 4

Photographs of (A) head and (B) entire holotype of Sternarchogiton porcinum, CAS 28810. Scale bars = 10 mm.

Figure 5

Photographs of (A) head and (B) entire live specimen of Sternarchogiton preto, MCP 37557 (female). Caudal appendage of this specimen naturally damaged and in process of regeneration. (C) Tail of an intact male preserved specimen, the holotype, MCP 37553, exhibits a prominent pale ring at base of caudal fin. Scale bars = 10 mm.

Figure 6

Photographs of (A) head and (B) entire holotype of Sternarchogiton labiatus, MCP 37544 (female). Scale bars = 10 mm.

Figure 7

Lower jaw of holotype of Sternarchogiton labiatus, MCP 37544 (female), illustrating diagnostic lateral swellings and medial, ventrally-orientated peg-like spur. (A) Lateral view, (B) ventral view, (C) frontal view. Right maxilla pushed medially to exhibit details of lips. Scale bars = 5 mm.

Contributor Notes

Section editor: J. W. Armbruster.

Received: 05 Oct 2005

Accepted: 14 Dec 2006