Sternarchorhynchus chaoi, Santana & Vari, 2010
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publication ID |
https://doi.org/ 10.1111/j.1096-3642.2009.00588.x |
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persistent identifier |
https://treatment.plazi.org/id/03E687C2-2844-FFAD-7CDD-FCB4A3C26661 |
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treatment provided by |
Valdenar |
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scientific name |
Sternarchorhynchus chaoi |
| status |
sp. nov. |
STERNARCHORHYNCHUS CHAOI View in CoL SP. NOV.
( FIGS 28 View Figure 28 , 31 View Figure 31 ; TABLE 5)
Diagnosis: Sternarchorhynchus chaoi is distinguished from congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the vertical through anterior nares, the absence of scales along the mid-dorsal region of the body as far posteriorly as the vertical through posterior limit of the pectoral fin, the presence of a more lightly coloured narrow band of mid-dorsal pigmentation on the head and mid-dorsal region of the body that extends posteriorly to the origin of the electroreceptive filament and sometimes beyond that point, the presence of eight to 13 premaxillary teeth, 15 precaudal vertebrae, 15–23 anterior unbranched anal-fin rays, 165–178 total anal-fin rays, and ten to 13 scales above the lateral line at the midbody, the greatest body depth (10.0–11.7% of LEA), the eye diameter (3.0–4.2% of HL), the head width (19.5–23.1% of SL), the postocular distance (39.1–41.3% of HL), and the caudal length (5.7–8.9% of LEA).
Description: Morphometric data for examined specimens in Table 5.
Lateral line extending posteriorly to point approximately three scales short of base of caudal fin and absent on remainder of tail and fin. Snout elongate, compressed and nearly straight to slightly curved ventrally distally. Mouth terminal and relatively small, with rictus located within area delimited by verticals running slightly anterior to and slightly posterior of anterior naris. Anus and urogenital papilla located ventral to head, with their position somewhat ontogenetically variable in available sample. Anus and urogenital papilla located along vertical approximately three orbital diameters posterior of rear margin of eye in smaller specimens and very slightly posterior of, or along, vertical through eye in larger individuals. Combined opening for anus and urogenital papilla ovoid in one apparent female and somewhat more horizontally elongate in juveniles and apparent males.
Premaxilla with eight to 13 teeth (N = 11) apparent in whole specimens. Dentary with two tooth rows; outer row with seven to nine teeth and inner row with three to five teeth (N = 11).
Branchiostegal rays five; with first three rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 15 (12 anterior; three transitional; N = 11).
Pectoral-fin rays ii + 11–13 [13] (N = 11). Anal-fin origin located anterior to vertical through margin of opercle. Anterior unbranched anal-fin rays 15–23 [22] (N = 10). Total anal-fin rays 165–178 [176] (N = 10). Scales above lateral line at midbody 10–13 [12] (N = 11). Scales absent along mid-dorsal line for distance of one-quarter to one-third of distance between rear of head and origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located approximately at 67% of TL. Filament extending posteriorly to vertical through posterior terminus of base of anal fin or one to two scales beyond that point. Tail compressed and short, ending in small, moderate, lanceolate caudal fin. Caudal-fin rays 13–16 [14] (N = 8).
Coloration in alcohol: Overall coloration dark brown. Snout dark overall with stripe of darker pigmentation extending anteriorly from orbit for distance one-half to two-thirds length of snout. Dorsal region of dark pigmentation on head forms lateral margin of narrow,
Number of specimens indicated in parentheses.
somewhat obscure, lightly coloured mid-dorsal stripe. Stripe expands very slightly laterally over postocular region, but separated from lightly coloured mid-dorsal stripe on body by region of dark pigmentation. Middorsal lightly coloured stripe on body commences somewhat posterior of terminus of comparable stripe on head and extends varying degrees posteriorly, reaching to origin of electroreceptive filament in some individuals. Pectoral fin distinctly dusky with rays covered with small, dark chromatophores. Anal fin dusky with rays overlain by small, dark chromatophores. Basal portions of caudal fin dusky to distinctly dark, but with distal portions of fin hyaline.
Distribution: Sternarchorhynchus chaoi is only known from one locality in the Rio Jamari basin of the state of Rondônia, Brazil ( Fig. 28 View Figure 28 ).
Secondary sexual dimorphism: No clear sexual dimorphism is apparent in the limited available samples of S. chaoi .
Etymology: The species name, chaoi , is in honour of Ning Labish Chao of the Universidade Federal do Amazonas, who provided invaluable assistance and financial support to the first author during his studies of gymnotiforms in Manaus, Brazil.
Material examined
Holotype: – BRAZIL. Rondônia: Rio Jamari, Porto Velho, canal de desvio da (diversion canal of) UHE (Usina Hidroeléctica) Samuel (approximately 8°27′S, 63°30′W), collected by G. M. dos Santos, 7.vi.1998; INPA 28357 (155). GoogleMaps
Paratypes: – BRAZIL. Rondônia: Rio Jamari, Porto Velho, Canal de desvio da (diversion canal of) UHE (Usina Hidroeléctica) Samuel (approximately 8°27′S, 63°30′W), collected with holotype by G. M. dos Santos, 7.vi.1998; INPA 20851, 11 (126–174); USNM 391713, 1 (164) GoogleMaps .
Nontype specimens: – BRAZIL. Rondônia: amongst rocks above UHE (Usina Hidroeléctrica) Samuel (approximately 8°27′S, 63°30′W); INPA uncat., field number Polo 896, 7 (48–168) GoogleMaps .
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