Sternarchorhynchus villasboasi, 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 : 354-355

STERNARCHORHYNCHUS VILLASBOASI SP. NOV.

( FIGS 73 , 77 ; TABLE 14)

Diagnosis: Sternarchorhynchus villasboasi 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 lateral line extending posteriorly to the base of the caudal fin, the narrow, more lightly coloured mid-dorsal stripe on the head that sometimes extends posteriorly to the vertical through the insertion of the pectoral fin, the slightly dusky anal fin, the possession of eight to nine teeth on the premaxilla, eight to nine teeth in the outer row of the dentary, 20–21 anterior unbranched anal-fin rays, 160–166 total anal-fin rays, the length of the base of the anal fin (83.6–85.8% of LEA), the preanal distance (12.5–14.7% of LEA), the caudal length (11.9–13.1% of LEA), the distance from the anus to the anal-fin insertion (12.1–15.0% of HL), the pectoral-fin length (43.6–47.1% of HL), the head depth at the eye (27.4–30.6% of HL), the head depth at the nape (52.6–55.4%), the mouth length (5.8–7.3% of HL), the snout length (53.3.56.1% of HL), the distance from the posterior naris to eye (39.7–45.4% of HL), the postocular distance (44.4–46.0% of HL), the height of the branchial opening (13.7–15.4% of HL), the tail depth (12.2–14.2% of caudal length), and the caudal-fin length (25.0–36.6% of caudal length).

Description: Morphometric data for examined specimens in Table 14.

Lateral line extending posteriorly to base of caudal fin but absent on fin. Snout elongate, compressed and slightly curved ventrally distally. Mouth small and terminal, with rictus located slightly anterior of vertical running through anterior naris. Anus and urogenital papilla located ventral to head, with position apparently ontogenetically variable in limited available sample. Structures located slightly posterior of vertical running through eye in juvenile (97 mm TL) and slightly anterior of vertical through eye in single mature female (135 mm TL) and single mature male (136 mm TL). Opening for anus and urogenital papilla longitudinally ovoid both sexes.

Premaxilla with eight to nine teeth (N = 2) apparent in whole specimens. Dentary with two tooth rows; outer row with eight to nine teeth and inner row with three teeth (N = 2).

Branchiostegal rays five; with first to third rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 15–16 (12 anterior; three to four transitional; N = 3).

Pectoral-fin rays ii + 12–13 [ii + 12] (N = 3). Anal-fin origin located anterior to vertical through margin of opercle. Anterior unbranched anal-fin rays 20–22 [22] (N = 3). Total anal-fin rays 160–166 [164] (N = 3). Scales above lateral line at midbody ten to 12 [12] (N = 3). Scales clearly present along mid-dorsal line to origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located approximately at 64% of TL. Filament extending posteriorly to point located approximately two scales anterior of vertical running through terminus of base of anal fin in juvenile and single mature male, but extending posteriorly one scale past terminus of base of anal fin in single examined female. Tail compressed and moderate, ending in small, elongate caudal fin. Caudal-fin rays 16–17 [17] (N = 2).

Coloration in alcohol: Overall coloration of head and body brown but darker dorsally. Snout dark overall with stripe of distinctly darker pigmentation extending anteriorly from orbit to, or nearly to, tip of snout. Ventral portion of snout dark. This dark coloration along with dark pigmentation on dorsolateral region of snout delimits distinctly more lightly pigmented band running along lateral surface of snout. Middorsal region of head with narrow, lightly coloured band extending from tip of snout to point approximately two-thirds of distance to vertical through eye. Remainder of head and body dark along mid-dorsal region. Pectoral distinctly dusky with rays covered with small, dark chromatophores. Anal fin slightly dusky with rays overlain by dark chromatophores. Caudal fin dark with distal most margin hyaline.

Distribution: Sternarchorhynchus villasboasi is only known from the type locality in the Rio Xingu at the Cachoeira de Kaituká ( Fig. 73 ).

Secondary sexual dimorphism: The available sample of S. villasboasi included a single mature male (135 mm TL) and single mature female (136 mm TL) as indicated by the examination of the gonads. No sexual dimorphism was apparent between those two individuals, but these specimens demonstrate that the species matures at relatively small body sizes.

Ecology: Little information is available about the type locality of S. villasboasi other than that it was a rapids area in the Rio Xingu , Brazil (see also Camposda-Paz, 1999).

Etymology: The species name, villasboasi , is in honour of Orlando Villa Bôas, who was instrumental in the designation of the Xingu National Park, in recognition of his diverse endeavours to ameliorate the impact of development projects on the indigenous peoples of that region.

Material examined

Holotype: – BRAZIL. Pará : Rio Xingu, Cachoeira de Kaituká , at Altamira (3°12′S, 52°12′W), L. Rapp Py-Daniel and J. A. Zuanon, 9.x.1990; INPA 28361 (135, mature female).

Paratype: – BRAZIL. Pará : Rio Xingu, Cachoeira de Kaituká , at Altamira (3°12′S, 52°12′W) L. Rapp Py-Daniel and J. A. Zuanon, 1990; INPA 32084, 1 (136, mature male); INPA 3934, 1 (97) .

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 77. Sternarchorhynchus villasboasi sp. nov., holotype, female, 135 mm total length, INPA 28361; Brazil, Pará, Cachoeira de Kaituká, Rio Xingu.