Sternarchorhynchus yepezi, 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/03E687C2-28FB-FF6F-7F5F-FB86A5B86073 |
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treatment provided by |
Valdenar |
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scientific name |
Sternarchorhynchus yepezi |
| status |
sp. nov. |
STERNARCHORHYNCHUS YEPEZI View in CoL SP. NOV.
( FIGS 73 View Figure 73 , 75 View Figure 75 , 76 View Figure 76 ; TABLE 14)
Diagnosis: Sternarchorhynchus yepezi is distinguished from congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the vertical through the anterior nares, having sparse scales covered by skin along the mid-dorsal portion of the body anterior to the origin of the electroreceptive filament, the longitudinally ovoid, but not distinctly horizontally elongate combined opening for the anus and the urogenital papilla, the consistently light overall coloration of the head and body, the presence of very dark pigmentation in the region at the base of the anterior and lateral margins of the enlarged teeth on the bulbous dentary in mature males, the presence of a more lightly coloured narrow band of mid-dorsal pigmentation on the head and mid-dorsal region of the body extending posteriorly to the origin of the electroreceptive filament and sometimes beyond that point, the possession of seven teeth on the outer tooth row of the dentary, 15 precaudal vertebrae, 182–188 total analfin rays, the greatest body depth (11.3–13.2% of LEA), the caudal length (8.1–8.4% of LEA), the pectoral-fin length (43.1–44.2% of HL), the head depth at the eye (30.5–40.0% of HL), the head depth at the nape (48.2–
352 C. D. DE SANTANA and R. P. VARI
Number of specimens indicated in parentheses.
56.0% of HL), the snout length (58.7–61.7% of HL), the eye diameter (4.1–4.8% of HL), the interocular width (6.6–8.1% of HL), and the caudal-fin length (33.2–38.8% of caudal length).
Description: Morphometric data for holotype and paratypes in Table 14.
Lateral line extending to base of caudal fin but absent on fin. Snout elongate, compressed and notably curved ventrally distally. Posterior naris located closer to tip of snout than to anterior margin of eye. Branchial opening restricted and situated slightly anterior to vertical through pectoral-fin origin. Location of anus and urogenital papilla sexually dimorphic based on limited available sample. Structures in small individual (112 mm TL) and apparently mature female (177 mm TL) located along vertical running two orbital diameters posterior of eye. Males (280 mm TL) with definite patch of enlarged dentition on dentary with anus and urogenital papilla more anteriorly positioned and located along vertical running two orbital diameters anterior of anterior margin of orbit. Combined opening for anus and urogenital papillae longitudinally ovoid.
Premaxilla of small size, somewhat rounded, with five to eight teeth (N = 3). Dentary in males transversely expanded into dorsally bulbous structure rounded from dorsal view and bearing series of enlarged, posteriorly recurved teeth. Dentary in single examined juvenile (112 mm TL) less elongate and lacking such expansion. Form of dentary in adults without expansion of anterior portion of dentary unknown. Teeth in two rows, with total of 11 teeth, with seven teeth in outer row and four teeth on inner row (N = 1). Mouth terminal in juveniles and somewhat dorsally directed in males with expanded dentaries. Location of rictus ontogenetically variable. Rictus located slightly posterior to vertical through anterior naris in smallest examined specimen (112 mm TL), approximately at vertical through anterior naris in midsized specimen (177 mm TL) and clearly anterior of vertical running through that naris in largest examined individual (280 mm TL).
Branchiostegal rays five; with first to third rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 15 (two anterior; three transitional; N = 3).
Pectoral-fin rays ii + 13–14 [ii + 13] (N = 3). Position of anal-fin origin either ontogenetically variable or sexually dimorphic, but with underlying basis impossible to ascertain from limited available sample. Located slightly posterior of vertical through anterior margin of opercle in smallest examined specimen (112 mm TL), but positioned along vertical slightly anterior of midpoint between anterior margin of opercle and posterior margin of eye in largest examined specimen (male, 280 mm TL). Anterior unbranched anal-fin rays 23–29 [29] (N = 3). Total anal-fin rays 182–188 [187] (N = 3). Scales above lateral line at midbody nine to 12 [11] (N = 3). Scales along mid-dorsal region of body somewhat sparse and not readily apparent on surface. Origin of midsaggital electroreceptive filament located approximately at 65% of TL. Filament in specimens of all sizes extending to vertical through posterior terminus of base of anal fin. Tail compressed and short, ending in very small, somewhat elongate caudal fin. Caudal-fin rays 16–17 [17] (N = 2).
Coloration in alcohol: Overall ground coloration tan to light greyish-tan. Snout ranging from nearly hyaline in small and midsized specimens to slightly grey in larger male with anteriorly expanded lower jaw bearing patch of distinct enlarged teeth. Skin around base of outer margin of patch of enlarged teeth in that male much more darkly pigmented than adjoining areas. Lower jaw without such dark pigmentation in other examined specimens (presumably females and juveniles). Snout in all specimens with distinct, narrow, anteriorly attenuating band of somewhat darker pigmentation extending from region anterior of eye to anterior portion of snout. Dark stripe nearly completely masked by ground coloration in examined males. Dark pigmentation on snout forms lateral border of narrow, more lightly coloured mid-dorsal band on head that continues from tip of snout to posterior margin of head. More lightly pigmented mid-dorsal band on head continuous posteriorly with lightly coloured mid-dorsal stripe extending along body to origin of electroreceptive filament.
Pectoral fin hyaline in smallest examined specimen, with some scattered dark pigmentation in somewhat larger female and with fin rays overlain by series of dark chromatophores in largest examined individual. Anal fin hyaline in small specimen and female paratype, with dark chromatophores overlying fin rays in male (largest specimen examined). Caudal fin hyaline or with faint dark pigmentation.
Distribution: The limited available samples of S. yepezi all originated in the central portions of the Río Orinoco basin in Venezuela ( Fig. 73 View Figure 73 ). The range of the species possibly extends to the Peruvian Amazon (see discussion under Remarks; also under Possible additional undescribed species).
Secondary sexual dimorphism: Males of S. yepezi share the anteriorly extended and laterally enlarged anterior portion of the dentary and associated patch of enlarged teeth present in some congeners. These mature males also have the anus and urogenital papilla more anteriorly positioned than do females and juveniles, but with the degree of difference in the position of those structures less pronounced than that present in some congeners. The reduction is both a consequence of the relatively more anterior position of the anus and urogenital papilla in the immature specimens and in the less distinctly advanced position of those structures in the single examined male with sexually dimorphic modifications of the lower jaw. It is possible that the examination of more extensive series of specimens will demonstrate a more pronounced degree of sexual dimorphism in this feature.
Etymology: The species name, yepezi , is in honour of Augustin Fernández-Yépez whose research on Sternarchorhynchus demonstrated that the diversity within the genus was greater than then recognized.
Remarks: Two specimens from the Peruvian Amazon examined during this study are very similar in many details to S. yepezi or more likely represent yet another undescribed species of the genus (see Possible additional undescribed species, below).
Material examined
Holotype: – VENEZUELA. Portuguesa: Río Portuguesa, fort at Nueva Florida, Santa Rosalía (approximately 8°57′N, 69°01′W), MCNG 44286 (280), collected by O. Castillo and RNR students, 2001. GoogleMaps
Paratypes: – VENEZUELA. Apure: Río Apure, between mouth of Río Portuguesa and San Fernando de Apure (7°54′N, 67°32′W), ANSP 165222, 2 (112– 177), collected by S. A. Schaefer et al., 4.xi.1989 GoogleMaps .
Nontype specimens: – VENEZUELA. Apure: Río Chirere , in Camachero, MBUCV-V-17394, 1 (320).
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