Sternarchorhynchus higuchii, 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 : 307-310

STERNARCHORHYNCHUS HIGUCHII SP. NOV.

( FIGS 42 , 45 , 46 ; TABLE 8)

Diagnosis: Sternarchorhynchus higuchii is distinguished from congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the vertical through anterior nares, the presence of scales although sometimes sparse and covered by skin along the mid-dorsal region of the body to the origin of the electroreceptive filament, the presence of an obscure, more lightly coloured, narrow band of middorsal pigmentation on the head and anterior middorsal region of the body, the slightly dusky anal fin without a distinct dark band along its distal margin, the lateral line extending posteriorly to a point approximately four to seven scales short of the base of the anal fin, the possession of two rows of dentary teeth with the outer row having nine to ten teeth, 23–31 anterior unbranched anal-fin rays, 162–178 total anal-fin rays, eight to 12 scales above the lateral line at the midbody, ten to 12 caudal-fin rays, the caudal length (14.7–18.9% of LEA), and the tail depth (5.9–7.5% of caudal length).

Description: Morphometric data for holotype and paratypes in Table 8.

Lateral line falling short of base of caudal fin by distance equal to four to seven scales and absent on remainder of tail and on caudal fin. Snout elongate, compressed and slightly curved ventrally distally. Posterior naris closer to tip of snout than to anterior margin of orbit. Branchial opening restricted and situated slightly anterior to vertical through pectoralfin origin. Location of anus and urogenital papilla apparently sexually dimorphic. Anus and urogenital papilla in smaller individuals and apparently mature females located within area between vertical located two orbital diameters posterior of orbit and vertical running through eye. Males with definite patch of enlarged dentition on dentary with anus and urogenital papilla more anteriorly positioned, located along verticals two to four orbital diameters anterior of anterior margin of eye (most anterior position approximately one-quarter of distance between anterior margin of orbit and tip of snout). Combined opening for anus and urogenital papilla distinctly elongate longitudinally.

Premaxilla of small size, somewhat rounded, with seven to eight teeth (N = 5). Dentary with two tooth rows with six curved conical teeth in outer row and three to four teeth on inner row (N = 5) in juveniles and females. Mature males demonstrating sexual dimorphism in lower jaw with anterior portion of dentary 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 dorsally directed in males with anteriorly and transversely expanded dentaries. Rictus located slightly anterior to vertical through anterior naris in all specimens.

Branchiostegal rays five; with first to third rays relatively narrow and elongate and remaining rays large and broad. Precaudal vertebrae 15–16 (12–13 anterior; two to four transitional; N = 16).

Pectoral-fin rays ii + 11–13 [ii + 13] (N = 14). Analfin origin located slightly posterior of vertical through anterior margin of opercle. Anterior unbranched analfin rays 23–31 [28] (N = 14). Total anal-fin rays 162– 178 [171] (N = 15). Scales above lateral line at midbody eight to 12 [10] (N = 16). Scales along middorsal region of body present, but somewhat sparse and not readily apparent on body surface. Origin of midsaggital electroreceptive filament located approximately at 59% of TL. Filament in specimens of all sizes extending six to eight scales posterior of vertical through posterior terminus of base of anal fin. Tail compressed and long, ending in very small, somewhat elongate caudal fin. Caudal-fin rays ten to 12 [11] (N = 11).

Coloration in alcohol: Overall ground coloration dark brown. Snout with variably distinct, narrow band of slightly darker pigmentation extending from region somewhat in advance of eye to anterior portion of snout. Second stripe of dark pigmentation running ventrally on snout to lower jaw. Two dark stripes delimit intermediate, more lightly pigmented region running along lateral surface of snout. Dorsal band of dark pigmentation forms lateral border of narrow, lightly coloured, mid-dorsal band on head that terminates posteriorly in region dorsal to eye. Body pigmentation very slightly darker dorsally and without distinct mid-dorsal lightly coloured stripe present in that region in many congeners. Middorsal region of body irregularly less intensely pigmented in some individuals, but with these lighter areas not confluent and not forming distinct, narrow stripe.

Pectoral fin coloration dark in all specimens, with dark chromatophores overlying fin rays. All examined specimens with anal fin dusky and posterior margin of fin-rays outlined by series of dark chromatophores. Caudal fin dark overall, but with distal margin hyaline.

Sexually dimorphic features for S. inpai 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 one specimen of 222 mm total length. Number of specimens indicated in parentheses.

310 C. D. DE SANTANA and R. P. VARI

Distribution: All examined specimens of S. higuchii were collected at the Cachoeira do Miriti and Cachoeira do Morena in the Rio Uatumã in the eastern portions of Amazonas, Brazil ( Fig. 42 ).

Secondary sexual dimorphism: Mature males of S. higuchii have an anteriorly extended and laterally enlarged anterior portion of the dentary with the associated patch of enlarged teeth. Males bearing such elaborations of the lower jaw and dentary teeth have the anus and urogenital papilla more anteriorly positioned than in examined conspecifics of comparable body sizes. Both the anus and urogenital papillae in these males are located distinctly anterior of the vertical through the eye, rather than at, or posterior of, that position as in males lacking modified dentaries and associated dentition. Females and juveniles similarly have these structures in a posterior position. Examined females of S. higuchii with mature ovaries are smaller than available males demonstrating sexual dimorphism in the lower jaw and dentary dentition.

Etymology: The species name, higuchii , is in honour of Horácio Higuchi of the Museu Paraense Emilio Goeldi, who provided invaluable assistance to the first author during his early studies of gymnotiforms.

Remarks: Sternarchorhynchus higuchii was collected at the same type locality as S. jaimei . The two species differ in the posterior extent of the lateral line (falling short of base of caudal fin by four to seven scales versus reaching the base of the caudal fin, respectively), total anal-fin rays (162–178 versus 180–195, respectively), the pigmentation of the mid-dorsal region of the body anterior to the origin of the electroreceptive filament (dark versus with narrow, lightly coloured stripe, respectively), and caudal depth (5.9–7.5 versus 10.1–19.2% of caudal length, respectively), and nearly completely in body depth (8.7–11.0 versus 10.8–12.6 of LEA, respectively).

Material examined

Holotype: – BRAZIL. Amazonas : Rio Uatumã, Cachoeira do Miriti, Presidente Figueredo (approximately 2°01′S, 59°28′W), INPA 28358 (246), collected by E. Ferreira, R. Leite, and S. Kullander, 4.x.1987.

Paratypes: – BRAZIL. Amazonas : Rio Uatumã, Cachoeira do Miriti, Presidente Figueredo (approximately 2°01′S, 59°28′W), collected by E. Ferreira, R. Leite, and S. Kullander, with holotype, INPA 20855, 15 (88–243); USNM 391714, 1 (189) .

Nontype specimens: – BRAZIL. Amazonas: Rio Uatumã, Cachoeira do Miriti (approximately 2°01′S, 59°28′W), INPA uncat., 2 (158–181). Rio Uatumã, Cachoeira do Morena, INPA 20854, 25 (125–233).

Figures

Figure 42. Map of central and northern South America showing geographical distribution of Sternarchorhynchus goeldii sp. nov. (1 = holotype locality; species also collected in region of type locality of Sternarchorhynchus higuchii sp. nov., star), Sternarchorhynchus hagedornae sp. nov. (2 = holotype locality), S. higuchii sp. nov. (3 = holotype locality), and Sternarchorhynchus inpai sp. nov. (4 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 45. Sternarchorhynchus higuchii sp. nov., holotype, sexually dimorphic male demonstrating modifications of dentary and dentary dentition, 246 mm total length, INPA 28358; Brazil, Amazonas, Cachoeira do Miriti, Rio Uatumã.

Figure 46. Sternarchorhynchus higuchii sp. nov., female, 180 mm total length, INPA 20855; Brazil, Amazonas, Cachoeira do Miriti, Rio Uatumã.