James S. Albert & William G. R. Crampton, 2003, Seven new species of the Neotropical electric fish Gymnotus (Teleostei, Gymnotiformes) with a redescription of G. carapo (Linnaeus)., Zootaxa 287, pp. 1-54 : 6

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Monophyly and Species-Groups of Gymnotus   ZBK

Gymnotus   ZBK is unique among gymnotiform fishes in possessing a superior mouth with a prognathous lower jaw; a thick and fleshy pad of tuberous electroreceptor organs and insulating support tissues overlying the tip of the snout and oral jaws; a pair of dorsally oriented pipe-shaped anterior nares partially or entirely included within the gape; a ventrally curved rictus; a lateral position of the eye on the head, about horizontal with the anterior oral margin; numerous long rami of the posterior lateral line extending ventrally on the caudal portion of the body; and a very long body cavity, with 31-51 precaudal vertebrae (Albert 2001; Albert & Crampton 2001).

Albert & Miller (1995) and Albert (2001) recognize three species-groups within the genus based on color pattern and body proportions, the G. cylindricus   ZBK , G. pantherinus , and G. carapo   ZBK species-groups. The species composition and geographical range of these groups are summarized in Table 1. The G. cylindricus   ZBK species-group is represented by two species endemic to the Atlantic and Pacific drainages of Middle America. The G. pantherinus species-group is represented by 12 species including those described herein, with distributions from Panama to Paraguay. Members of the G. pantherinus species-group can be distinguished from those in the other two species-groups by the possession of: a slender body (adult modal BD 6.1-9.0% TL [except G. melanopleura   ZBK ] vs. 9.1-11.7% in all other Gymnotus   ZBK species except G. henni n. sp. and G. esmeraldas   ZBK n. sp.); proximal portion of fifth rib with broad triangular ridge, more than three times width of sixth rib (vs. narrow ridge, less than three times width of sixth rib); dentary hook at mental symphysis composed of paired ventroposterior oriented processes. The G. carapo   ZBK species-group is endemic to South America and is represented by 12 species, including those described herein, with distributions from the Pacific slope of Colombia to the Pampas of Argentina. Members of the G. carapo   ZBK species-group can be distinguished from those in the other two species-groups by the possession of: a clear or pale patch near the caudal end of the anal fin, most visible in juveniles and subadults (60-150 mm); two (vs. one) laterosensory pores in the dorso-posterior portion of preopercle, in the preopercular-mandibular canal. The classification of Gymnotus   ZBK into three species groups is used as a basis for diagnosing the new species described herein.