Sternarchorhynchus taphorni, 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 : 349-351

STERNARCHORHYNCHUS TAPHORNI SP. NOV.

( FIGS 73 , 74 ; TABLE 13)

Diagnosis: Sternarchorhynchus taphorni 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, the presence of a definite series of scales along the mid-dorsal region of the body, the presence of a narrow, more lightly coloured mid-dorsal stripe on the head and body extending posteriorly to the vertical through the insertion of the pectoral fin at least in smaller individuals, the dark anal fin, the lateral line terminating at a point approximately eight scales anterior of the base of the caudal fin, the possession of eight premaxillary teeth, ten teeth in total on the dentary, 14 branched pectoral-fin rays, 30 anterior unbranched anal-fin rays, 186 total anal-fin rays, 12–13 premaxillary teeth, the length of the anal-fin base (84.8% of LEA), the preanal distance (11.0% of LEA), the prepectoral-fin distance (18.8% of LEA), the pectoral-fin length (37.4–47.8% of HL), the caudal length (6.8% of LEA), the head length (18.9% of LEA), the snout length (51.1–62.2% of HL), the head depth at the eye (31.8–46.8% of HL), the head depth at the nape (55.7–62.3% of HL), the eye diameter (5.7–6.0% of HL), the distance from the posterior naris to the eye (35.9–52.4% of HL), the postocular distance (43.5–46.4% of HL), the interocular width (7.8–11.5% of HL), the length of the mouth (7.7–9.0% of HL), the height of the branchial opening (11.6– 14.8% of HL), the tail depth (24.4% of caudal length), and the caudal-fin length (50.2% of caudal length).

Description: Morphometric data for holotype and nontype specimens in Table 13.

Lateral line extending to position about eight scales anterior of hypural joint and absent on remainder of tail and on caudal fin. Snout elongate, compressed and notably curved ventrally distally. Posterior naris 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 apparently both ontogenetically and sexually dimorphic based on limited available sample. Anus and urogenital papilla in small individual located along vertical running three orbital diameters posterior of eye. Midsized specimen with those structures located along vertical through eye. Larger male with patch of enlarged dentition on expanded dentary having anus and urogenital papilla more anteriorly positioned and located along vertical two orbital diameters anterior of anterior margin of orbit. Combined opening for anus and urogenital papilla longitudinally ovoid.

Premaxilla of small size, somewhat rounded, with eight teeth (N = 1). Dentary with two rows of irregularly arranged teeth with total of ten teeth. Male demonstrating sexual dimorphism in lower jaw with anterior portion of jaw extending further anteriorly than in females and juveniles and with dentary distinctly expanded laterally into dorsally bulbous structure rounded from dorsal view. Expanded portion of dentary bearing series of enlarged, slightly posteriorly recurved teeth. Mouth terminal in juveniles and females and somewhat anterodorsally directed in male with expanded dentary. Position of rictus ontogenetically slightly variable. Rictus located slightly posterior to vertical through anterior naris in smallest examined specimen (77 mm TL), approximately at, or slightly anterior of, vertical running through anterior naris in midsized specimen (216 mm TL) and in male with large patch of dentition on enlarged dentary (310 mm TL).

Branchiostegal rays five; with first to third rays somewhat narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 16 (13 anterior; three transitional; N = 1).

Pectoral-fin rays ii + 13–15 [ii + 15] (N = 3). Anal-fin origin variable, located posterior to vertical running through eye in small specimen (77 mm TL), along vertical running through eye in midsized specimen (216 mm TL), and anterior to vertical through eye in largest specimen (male with large patch of enlarged dentition on expanded dentary; 310 mm TL). Anterior unbranched anal-fin rays 30 (N = 1). Total anal-fin rays 186 (N = 1; largest specimen, only examined individual without regenerated tail and damaged posterior portion of anal fin). Scales above lateral line at midbody 11–12 [11] (N = 3). Scales along mid-dorsal region of body readily apparent on surface. Origin of midsaggital electroreceptive filament located distinctly posterior of midlength of body. Filament in large male (only specimen without regenerated tail and damaged posterior portion of anal fin) terminating posteriorly two scales anterior of vertical running through posterior terminus of base of anal fin. Tail compressed and short, ending in small, somewhat elongate caudal fin. Caudal-fin rays 14 (N = 1, largest specimen; only individual without regenerated caudal fin).

Coloration in alcohol: Overall ground coloration brown to dark brown. Snout in smallest specimen darker dorsolaterally and ventrally, with those areas separated by very narrow, distinctly more lightly coloured stripe. No such midlateral stripe on snout present in other specimens, although dorsal region of snout somewhat darker than lateral and ventral portion of that portion of head in midsized individual. Male with anteriorly expanded lower jaw bearing patch of distinct enlarged teeth having head very dark overall on lateral and ventral portions. Smallest specimen (77 mm TL) with narrow, lightly coloured, mid-dorsal stripe extending from snout along top of head and mid-dorsal portion of body as far posteriorly as vertical through posterior limit of pectoral fin. Stripe apparent but less extensive in larger specimens, reaching only to vertical about four orbital diameters posterior of rear of eye in midsized specimen (216 mm TL) and only to vertical running through anterior margin of eye in larger male (310 mm TL).

Pectoral fin variably dark in all specimens and particularly so in largest examined individual. Anal fin dark in all individuals, with chromatophores overlying fin rays. Dark pigmentation particularly intense along basal portion of fin in large male and forming posteriorly attenuating dark band. Caudal fin dark with distal portions less intensely pigmented.

Distribution: Examined specimens of S. taphorni originated in the upper portions of the Río Huallaga and adjoining left bank tributaries of the Río Ucayali basin of eastern Peru ( Fig. 73 ).

Secondary sexual dimorphism: The examined male of S. taphorni has an anteriorly extended and laterally enlarged anterior portion of the dentary with the associated patch of enlarged teeth comparable to the modifications of the jaw and teeth of some congeners. The male also has the anus and urogenital papilla more anteriorly positioned than in the examined female and juvenile.

Etymology: The species name, taphorni , is in honour of Donald Taphorn of the Universidad Nacional Experimental de los Llanos Occidentales, who generously assisted the authors with this and other publications over the years and who has made many contributions to our understanding of the South American freshwater fish fauna.

Remarks: The two paratypes of S. taphorni examined in this study agree with the holotype in examined details and were collected in the same general region in the Peruvian Amazon. The holotype originated, however, within the Río Huallaga system whereas the two nontypes came from tributaries of the Río Ucayali. The common presence of a species in both the Río Huallaga system and left bank tributaries of the Río Ucayali was reported by Vari & Harold (2001: 172) for the characid Creagrutus ortegai . Some tributaries of the Río Ucayali approach portions of the Río Huallaga system ( Isbrücker & Nijssen, 1983: fig. 5) and commonality of species across those portions of the two river basins may be found to be a phenomenon of greater generality once the ichthyofauna of that region is better explored ichthyologically.

Material examined

Holotype: – PERU. Departamento de San Martin: Río Huallaga, Uchiza (approximately 8°29″59″S, 76°22′59″W); MUSM 6635 (310), collected by L. P. Davilla, viii.1948.

Paratypes: – PERU. Departamento de Huánuco: Río Llullapichis , 2 km upstream from mouth into Río Pachitea (9°37′S, 74°57′W), ROM 55531, 1 (216), collected by E. Holm, B. Alvarado, H. Sisniegas. Río Llullapichis , 1.5 km west of Panguana Station (9°37′S, 74°57′W), ROM 55530, 1 (77.3), collected by E. Holm, B. Alvarado.

Figures

Figure 73. Map of central and northern South America showing geographical distribution of Sternarchorhynchus stewarti sp. nov. (1 = holotype locality), Sternarchorhynchus taphorni sp. nov. (2 = holotype locality), Sternarchorhynchus yepezi sp. nov. (3 = holotype locality; 4 = collecting location of possibly conspecific sample from central Amazon; under Remarks concerning that specimen and second specimen from aquarium trade possibly collected in the region of Iquitos, Peru), and Sternarchorhynchus villasboasi sp. nov. (5 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 74. Sternarchorhynchus taphorni sp. nov., holotype, sexually dimorphic male demonstrating modifications of dentary and dentary dentition, 310 mm total length, MUSM 6635; Peru, San Martin, Río Huallaga.