Sternarchorhynchus kokraimoro, 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 : 314-317

STERNARCHORHYNCHUS KOKRAIMORO SP. NOV.

( FIGS 50–52 ; TABLE 9)

Diagnosis: Sternarchorhynchus kokraimoro 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 absence of a more lightly coloured narrow band of mid-dorsal pigmentation on the head and mid-dorsal region of the body anterior of the origin of the electroreceptive filament, the dusky anal fin, the termination of the lateral line three to five scales anterior of the base of the caudal fin, the possession of seven to ten premaxillary teeth, two tooth rows on the dentary with eight to ten teeth in the outer row, 175–177 total anal-fin rays, eight to nine scales above the lateral line at the midbody, 16–17 precaudal vertebrae, 15 caudal-fin rays, the distance from the snout to the anus (13.6– 15.0% of LEA), the preanal distance (16.9–17.1% of LEA), the prepectoral-fin distance (23.1–24.0% of LEA), the head length (22.9–23.1% of LEA), the caudal length (14.3–15.5% of LEA), the distance from the anus to the anal-fin insertion (8.2–12.5% of HL), the head width (18.6–20.2% of HL), the snout length (63.7–66.2% of HL), and the interocular distance (4.6– 5.1% of HL).

Description: Morphometric data for examined specimens in Table 9.

Lateral line extending posteriorly to point approximately three to five scales anterior of base of caudal fin but absent on remainder of tail and on fin. Snout elongate, compressed and curved ventrally distally. Male with dorsomedial fleshy ridge on anterior half of snout; ridge absent in female. Ridge makes that portion of snout of male overall distinctly deeper than in female (compare Figs 51 , 52 ). Mouth moderate, with opening anterodorsally orientated, and rictus located at, or slightly posterior of, vertical through anterior naris. Dentary in mature male lengthened anteriorly, slightly expanded transversely and bearing patch of somewhat enlarged teeth. Anus and urogenital papilla located ventral to head, with position apparently sexually dimorphic in limited available sample. Anus and urogenital papilla positioned along vertical through eye in mature female and slightly more anteriorly in single mature male. Combined opening for anus and urogenital papilla ovoid in both sexes.

Premaxilla with seven to ten teeth (N = 2) apparent in whole specimens. Dentary with two tooth rows; outer row with eight to ten teeth and inner row with two to 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 16–17 (14 anterior; two to three transitional; N = 2).

Pectoral-fin rays ii + 12–13 [ii + 13] (N = 2). Anal-fin origin located anterior to vertical through margin of opercle. Anterior unbranched anal-fin rays 22–23 [23] (N = 2). Total anal-fin rays 175–177 [175] (N = 2). Scales above lateral line at midbody eight to nine [9] (N = 2). 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 vertical located two scales posterior of vertical through terminus of base of anal fin. Tail compressed and moderate, ending in small, elongate caudal fin. Caudal-fin rays 15 [15] (N = 2).

Coloration in alcohol: Overall coloration of head and body dark brown. Snout dark overall with stripe of distinctly darker pigmentation extending from orbit anteriorly to, or nearly to, tip of snout. Ventral portion of snout darkly pigmented; that pigmentation along with dark pigmentation on dorsolateral portion of snout delimits intermediate, more lightly coloured band running along lateral surface of snout. Head and body uniformly dark along mid-dorsal region contrary to condition present in many congeners. Pectoral fin distinctly dusky with rays covered with small, dark chromatophores. Anal fin slightly dusky, with rays overlain by spots of dark pigmentation. Caudal fin dark overall, but with distal most margin hyaline.

Distribution: Sternarchorhynchus kokraimoro is only known from the Cachoeira de Kaituká in the Rio Xingu ( Fig. 50 ).

Ecology: Little information is available about the type locality of S. kokraimoro other than that it was a rapids area in the northern portions of the Rio Xingu (also Campos-da-Paz, 1999).

Sexually dimorphic features for Sternarchorhynchus mareikeae are presented as two entries. First entry is data for all specimens other than sexually dimorphic mature males with information for sexually dimorphic male in second entry based on four specimens of 176–221 mm total length. Number of specimens indicated in parentheses.

Secondary sexual dimorphism: The single examined male of S. kokraimoro has the lower jaw lengthened and somewhat expanded laterally, albeit to a lesser degree than that in congeners that share this sexually dimorphic feature. The available material of the species does not permit us to determine whether the lesser degree of development of this feature is characteristic of S. kokraimoro or alternatively may represent ontogenetic variation or seasonality in the expression of that modification. The male also has a well-developed, mid-dorsal fleshy ridge along the anterior half of the snout that is lacking in the female (compare Figs 51 , 52 ). This feature is unique to this species within Sternarchorhynchus .

Etymology: The species name, kokraimoro , is in reference to the Kokraimoro, a group within the Kayabo tribe whose ancestral lands included the type locality of the species.

Material examined

Holotype: – BRAZIL. Pará : Rio Xingu, Cachoeira de Kaituká , at Altamira (3°12′S, 52°12′W), collected by L. Rapp Py-Daniel and J. A. Zuanon, 9.x.1990; INPA 28360 (197, mature male).

Paratype: – BRAZIL. Pará : Rio Xingu, Cachoeira de Kaituká, Altamira (3°12′S, 52°12′W), collected with holotype by L. Rapp Py-Daniel and J. A. Zuanon, 9.x.1990; INPA 3932, 1 (171, mature female) .

Figures

Figure 50. Map of central and northern South America showing geographical distribution of Sternarchorhynchus jaimei (1 = holotype locality), Sternarchorhynchus kokraimoro sp. nov. (2 = holotype locality), Sternarchorhynchus mareikeae sp. nov. (3 = holotype locality), Sternarchorhynchus marreroi sp. nov. (4 = holotype locality), and Sternarchorhynchus mendesi sp. nov. (5 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 51. Sternarchorhynchus kokraimoro sp. nov., holotype, male, showing deeper snout of males, 197 mm total length, INPA 28360; Brazil, Pará, Cachoeira de Kaituká, Rio Xingu.

Figure 52. Sternarchorhynchus kokraimoro sp. nov., paratype, female, 171 mm total length, INPA 3932; Brazil, Pará, Cachoeira de Kaituká, Rio Xingu.