[[Sternarchorhynchus Castelnau]]

Species of the tube-snouted electric knifefish genus Sternarchorhynchus Castelnau, are common components of the deepwater benthic fauna of many large rivers throughout the Atlantic drainages of South America (Lopez-Rojas et al., 1984; Lundberg et al., 1987; Marrero, 1987; Marrero et al., 1987; Marrero & Taphorn, 1991; Marrero & Winemiller, 1993; Barletta, 1995; Garcia, 1995; Lasso et al., 1997; Campos-da-Paz, 2000; CoxFernandes, 1999; Cox-Fernandes et al., 2004). Sternarchorhynchus species generate weak periodic (wave-type) electric organ discharges (EODs) with known rates of 944-1992 Hz (Kramer et al., 1981; Crampton, 1998; Crampton & Albert, 2006). Currently, six valid species of Sternarchorhynchus are recognized (Mago-Leccia, 1994; Campos-da-Paz, 2000; Albert, 2003), of which four are known from the upper Amazon basin in Brazil: S. mormyrus (Steindachner), S. roseni Mago-Leccia, S. oxyrhynchus (Müller & Troschel), and S. cf. curvirostris (Barletta, 1995; Crampton, 1998; Cox-Fernandes et al., 2004; Crampton & Albert, 2006). Sternarchorhynchus roseni is also known from the Orinoco basin, and S. oxyrhynchus is known from the Orinoco and Essequibo basins (Lopez-Rojas et al., 1984; Marrero & Taphorn, 1991; Mago-Leccia, 1994). Sternarchorhynchus curvirostris (Boulenger) was originally described from Canelos, Ecuador (Mago-Leccia, 1994). Sternarchorhynchus britskii Campos-da-Paz is known from the Paraná River basin, and S. mesensis Campos-da-Paz is known from the upper Tocantins River basin (Camposda-Paz, 2000).

Sternarchorhynchus is unquestionably represented by many other undescribed species (e.g., Campos-da-Paz, 1992; Crampton & Albert, 2006) and is currently the most diverse genus in the Sternarchorhynchinae (Albert, 2001). This contrasts with several apteronotid genera that have low species-level diversity, including the monotypic genera Sternarchorhamphus Eigenmann, Orthosternarchus Boulenger, Parapteronotus Albert, and Platyurosternarchus Mago-Leccia (Mago-Leccia, 1994; Albert & Campos-da-Paz, 1998; Albert, 2001; Albert & Crampton, 2005).

At least one species of Sternarchorhynchus, S. roseni, is known to exhibit a sexual dimorphism in which males develop a crown of external teeth on the lower jaw (MagoLeccia, 1994; Py-Daniel & Cox-Fernandes, 2005). Sternarchorhychus mormyrus exhibits variation in cranial morphology, with mature males exhibiting a wider snout than females (pers. obs.). The remaining described species of Stenarchorhynchus exhibit no dimorphism (Mago-Leccia, 1994; Campos-da-Paz, 1992, 2000). Here we describe a new species from deepwater channels of the lowland Amazon basin of Brazil, with information on its electric organ discharges and ecology.