Sternarchorhynchus marreroi, 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 : 318-320

STERNARCHORHYNCHUS MARREROI SP. NOV.

( FIGS 50 , 55 ; TABLE 9)

Diagnosis: Sternarchorhynchus marreroi 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 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 hyaline anal fin with slight dusky pigmentation distally in some specimens, the extension of the lateral line posteriorly to a point four to five scales anterior of the base of the caudal fin, the possession of eight premaxillary teeth, two rows of teeth on the dentary with eight teeth in the outer row, 14 caudal-fin rays, 15 precaudal vertebrae, 21–31 anterior unbranched anal-fin rays, 162–181 total anal-fin rays, ten to 11 scales above the lateral line at the midbody, 14 caudal-fin rays, the greatest body depth (11.2–14.1% of LEA), the distance from the snout to the anus (5.8–9.0% of LEA), the distance from the anus to the anal-fin insertion (10.1–17.6% of HL), the preanal distance (9.2–10.8% of LEA), the prepectoral-fin distance (17.0–17.6% of LEA), the head length (16.4–16.6% of LEA), the caudal length (8.8–10.9% of LEA), the distance from the posterior naris to the snout (6.4–7.9% of HL), the head width (25.9–29.9% of HL), the pectoral-fin length (45.7–75.8% of HL), the head depth at the eye (32.9–35.4% of HL), the head depth at the nape (55.1–65.5% of HL), the snout length (62.3–63.6% of HL), the distance from the posterior naris to the eye (48.8–53.4% of HL), the internarial distance (3.0– 4.3% of HL), the interocular width (6.8–8.1% of HL), the height of the branchial opening (15.3–19.6% of HL), the postocular distance (45.3–49.0% of HL), and the tail depth (15.7–20.2% of caudal length).

Description: Morphometric data for examined specimens in Table 9.

Lateral line extending posteriorly to point approximately four or five scales short of base of caudal fin, but absent on remainder of tail and fin. Snout elongate, compressed and distinctly curved ventrally. Mouth terminal and relatively small, with rictus located slightly posterior to vertical through posterior naris. Anus and urogenital papilla located ventral to head, with position apparently ontogenetically somewhat variable. Openings positioned along vertical slightly posterior of rear margin of eye in smaller specimens and along vertical two orbital diameters anterior of anterior margin of orbit in larger individuals. Combined opening for anus and urogenital papilla longitudinally ovoid.

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

Branchiostegal rays five; with first three rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 15 (12–13 anterior; two to three 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 21–31 [30] (N = 3). Total anal-fin rays 162–181 [162] (N = 3). Scales above lateral line at midbody ten to 11 [10] (N = 3). Scales present along mid-dorsal line to origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located approximately at 60% of TL. Filament extending posteriorly to point two to five scales anterior of vertical through posterior terminus of base of anal fin. Tail compressed and short, ending in small, moderate, pointed caudal fin. Caudal-fin rays 14 [14] (N = 2).

Coloration in alcohol: Overall coloration ranging from light to medium brown, but missing on some regions because of apparent postmortem damage. Head with narrow stripe of slightly darker pigmentation extending anteriorly from orbit for distance a half to twothirds length of snout. Darker pigmentation forms lateral margin of lightly coloured mid-dorsal stripe on snout. Lightly coloured stripe expands posteriorly into longitudinally elongate ovoid, lightly coloured area located above postocular portion of head. Ovoid region continuous posteriorly with mid-dorsal, lightly coloured stripe on body that extends posteriorly for varying degrees towards origin of electroreceptive filament. Pectoral fin dark distally and dorsally. Anal fin hyaline overall, but with distal portions slightly dusky in largest examined specimen. Caudal fin dusky to dark.

Distribution: Sternarchorhynchus marreroi is known from the central and delta regions of the Río Orinoco ( Fig. 50 ).

Secondary sexual dimorphism: No sexual dimorphism is apparent in the limited available samples of S. marreroi .

Etymology: The name, marreroi , is in honour of Críspulo Marrero of the Universidad Nacional Experimental de los Llanos Occidentales, who has greatly contributed to our knowledge of the biology of gymnotiforms in Venezuela.

Material examined

Holotype: – VENEZUELA. Apure: Río Apure, in front of Isla Apurito , left bank (8°00′N, 67°31′W), collected by O. Castillo and F. Provenzano, 25.i.1984; MBUCV 15806 (182).

Paratypes: – VENEZUELA. Apure: Río Apure, in front of Isla Apurito, left bank (8°00′N, 67°31′W), collected with holotype by O. Castillo and F. Provenzano, 25.i.1984; MBUCV 33750, 1 (278; formerly MBUCV V-15806, in part). Delta Amacuro : Río Orinoco , south of Isla Portuguesa (approximately 8°37′N, 61°49′W), collected by J. G. Lundberg et al., 20.ii.1978; MBUCV 10637, 1 (231).

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 55. Sternarchorhynchus marreroi sp. nov., holotype, presumably female, 182 mm total length, MBUCV 15806; Venezuela, Apure, Río Apure.