Sternarchorhynchus axelrodi, Santana & Vari, 2010

Santana, Carlos David De & Vari, Richard P., 2010, Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies, Zoological Journal of the Linnean Society 159 (1), pp. 223-371 : 275

STERNARCHORHYNCHUS AXELRODI SP. NOV.

( FIGS 26–28 ; TABLE 4)

Sternarchorhynchus cf. mormyrus , Campos-da-Paz, 2000: 533 [ Brazil, Rio Tocantins; as probable undescribed species].

Sternarchorhynchus mormyrus , not of Steindachner, dos Santos et al., 2004: 103, unnumbered figure [ Brazil, lower Rio Tocantins; food habits].

Diagnosis: Sternarchorhynchus axelrodi is distinguished from all congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the vertical through the anterior nares, the absence of scales along the mid-dorsal region of the body as far posteriorly as the origin of the electroreceptive filament, and the possession of 200–217 anal-fin rays.

Description: Morphometric data for examined specimens in Table 4.

Lateral line extending posteriorly to base of caudal fin, but absent on fin. Snout elongate, compressed and curved ventrally, and with sexual dimorphism in overall form across examined specimens of large body sizes. Snout more anteroventrally aligned in mature females than in mature males of comparable sizes as evidenced by specimens of each sex with mature gonads. Sexual dimorphism in form of lower jaw and associated dentition found in many congeners not apparent in examined samples. Mouth terminal, rictus situated anterior of vertical through anterior naris. Anus and urogenital papilla located ventral to head, with openings situated anterior to vertical through anterior margin of eye (in specimens of 433– 510 mm SL). Combined opening for anus and urogenital papilla distinctly elongate longitudinally and bordered laterally by raised fleshy ridges.

Premaxilla with six to ten teeth apparent in whole specimens (N = 4). Dentary with one tooth row consisting of nine to 15 curved conical teeth in whole specimens (N = 4), with second row of apparent replacement teeth located internal to functional row.

Branchiostegal rays five; with first to third rays apparently narrow and elongate in radiographs, and with fourth and fifth rays clearly very large and broad. Precaudal vertebrae 18–19 (15 anterior; three to four transitional; N = 10).

Pectoral-fin rays ii + 13–17 [ii + 16] (N = 10). Analfin origin located anterior to opercle. Anterior unbranched anal-fin rays 22–34 [33] (N = 5). Total anal-fin rays 200–217 [205] (N = 10). Scales above lateral line at midbody nine to 11 [11] (N = 10). Scales absent along much of mid-dorsal line in region anterior to origin of midsaggital electroreceptive filament. Areas lacking scales sometimes separated by regions covered by mid-dorsal scales, but with position and extent of regions lacking scales variable across examined specimens. Origin of midsaggital electroreceptive filament located approximately at 65% of TL.

Figures

Figure 26. Sternarchorhynchus axelrodi sp. nov., holotype, male, 444 mm total length, MNRJ 31279; Brazil, Goiás, Rio Tocantins.

Figure 27. Sternarchorhynchus axelrodi sp. nov., paratype, female, 493 mm total length, MNRJ 12168; Brazil, Goiás, Rio Tocantins; showing more pronounced ventral curvature of snout in mature females of species.

Figure 28. Map of central and northern South America showing geographical distribution of Sternarchorhynchus axelrodi sp. nov. (1 = holotype locality), Sternarchorhynchus britskii, Sternarchorhynchus caboclo, Sternarchorhynchus chaoi sp. nov. (2 = holotype locality), and Sternarchorhynchus cramptoni sp. nov. (3 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).