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[[Gymnotus (L.)]] Introduction Gymnotus (L.) is a monophyletic group of gymnotiform fishes that is readily recognizable by the presence of a superior mouth with a prognathous lower jaw, a fleshy pad of electroreceptor organs and support tissues over the tip of the snout and mandible, a pair of dorsally oriented pipe-shaped anterior nares partially or entirely included within the gape, a ventrally curved rictus, the lateral position of the eyes on the head (at a horizontal with the gape), numerous long rami of the posterior lateral line extending ventrally on the caudal portion of the body, and a very long body cavity with 31-48 precaudal vertebrae (Albert 2001; Albert et al. 2005). Most Gymnotus species possess obliquely oriented bands of dark and light pigments along the length of the body from which they derive the English common name “banded knife-fish.” Gymnotus species extend from the Pampas of Argentina (36 °S) to Chiapas, Mexico (18 °N) and are known from the continental waters of all South and Middle American countries except Chile and Belize (Albert 2001). Many species of Gymnotus exhibit sizable variation in body shape and color patterns within and between populations (MagoLeccia1994; Albert & Miller 1995; Albert et al. 1999). Since these features are also used to recognize Gymnotus species, much of the diversity in the group remains undocumented and many undescribed species exist in museum collections and in the wild (Nelson, 1994, Albert et al. 1999; Albert 2001). There are currently 31 species of Gymnotus recognized (Albert et al. 2005). As for many Neotropical freshwater fishes, species diversity of this group is greatest in the Amazon basin where 15 species are known, 10 of which inhabit vrzea Whitewater floodplains (Albert & Crampton 2001, Crampton et al. 2003). Fewer data are available on species diversity, distributions and population structure of this group in other Neotropical basins (Fernandes-Matioli et al. 2000). In central and southeastern Brazil many specimens are ascribed to G. carapo L., the type locality of which is in Surinam (Albert 2001). Three other Gymnotus species have been recognized from central and southeastern Brazil: G. pantherinus (Steindachner) from the coastal drainages of southeastern, Brazil, G. inaequilabiatus (Valenciennes) from the Parana-Paraguay basin and some coastal drainages of Uruguay and southeastern Brazil, and G. sylvius (Albert et al. 1999) from coastal drainages of São Paulo State and the Rio Paraná basin. Here we describe a new species discovered by one of us (FMCF) as part of a survey of population structure and genealogical/coalescent analysis of Gymnotus from the Pantanal Matogrossense, Brazil. |
