Sternarchorhynchus cramptoni, 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 : 288-291

STERNARCHORHYNCHUS CRAMPTONI SP. NOV.

( FIGS 28 , 32 , 33 ; TABLE 5) Sternarchorhynchus cf. roseni, Rapp Py-Daniel & Cox-Fernandes, 2005: 105 , fig. 5. [ Brazil, Amazon Basin; secondary sexual dimorphics in form of lower jaw].

Diagnosis: Sternarchorhynchus cramptoni 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 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 anterior of the origin of the electroreceptive filament and sometimes beyond that point, the presence of a dark band along the distal one-fifth to one-half of much of the anal fin and over most of the posterior rays of that fin, the presence of eight to 12 teeth on the premaxilla, six to eight teeth on the outer tooth row of the dentary, 180–221 total anal-fin-rays, 16 precaudal vertebrae, the preanal distance (10.9– 14.9 of LEA), the greatest body depth (9.7–12.1% of LEA), the caudal length (5.0–8.4% of LEA), the head length (16.0–19.5% of LEA), the distance from the anus to the anal-fin insertion (6.7–12.3% of HL), the snout length (60.6–67.0% of HL), the head depth at the nape (46.2–58.8% of HL), the postocular distance (37.4–43.7% of HL), the prepectoral-fin distance (16.5–20.3% of HL), the tail depth (23.6–29.6% of caudal length), and the caudal-fin length (30.9–61.4% of caudal length).

Description: Morphometric data for holotype and paratypes in Table 5.

Lateral line extending to base of caudal fin, but absent on fin. Snout elongate, compressed and curved ventrally distally. Posterior naris located 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 ontogenetically variable and apparently sexually dimorphic. Anus and urogenital opening in smaller individuals positioned along vertical located slight distance posterior of vertical through rear margin of eye. Larger specimens lacking secondary male characters with two openings located at vertical running slightly anterior of anterior margin of eye. Males with patch of large teeth at anterior of expanded dentary with anus and urogenital papilla positioned more anteriorly at vertical about one-third of distance between anterior margin of eye and tip of snout. Aperture for anus and urogenital opening rounded in juveniles and apparent females; longitudinally elongate in males demonstrating sexually dimorphic modifications of dentary and associated dentition.

Premaxilla of small size, somewhat rounded, with eight to 12 teeth (N = 6). Dentary elongate with fleshy pad on anteroventral surface in larger specimens. Dentaries approximately of same length in males and females, but with form sexually dimorphic. Anterior portion of dentary of males somewhat widened laterally into moderately dorsally bulbous structure bearing enlarged teeth (degree of expansion of dentary and of enlargement of teeth less pronounced than that present in some congeners). Dentary with two rows of curved conical teeth. Outer row with six to eight teeth (N = 10) and inner row with three to four teeth (N = 8). Mouth terminal with rictus located anterior to vertical through posterior naris in juveniles. Rictus slightly more posteriorly positioned in larger individuals.

Branchiostegal rays five; with first to third rays relatively narrow and elongate and remaining rays large and broad. Precaudal vertebrae 16 (12–13 anterior; three to four transitional, N = 11).

Pectoral-fin rays ii + 11–14 [ii + 14] (N = 30). Analfin origin located slightly posterior of vertical through anterior margin of opercle. Anterior unbranched analfin rays 17–29 [24] (N = 15). Total anal-fin rays 180– 221 [221] (N = 24); number of rays apparently increases ontogenetically given evident correlation between greater body size and increased numbers of anal-fin rays amongst examined specimens. Scales above lateral line at midbody 9–12 [9] (N = 33). Scales along mid-dorsal region of body readily apparent. Origin of midsaggital electroreceptive filament located approximately at 62% of TL. Filament extending posteriorly to vertical running through to posterior terminus of base of anal fin. Tail compressed and short, ending in small, caudal fin with rounded distal margin. Caudal-fin rays 13–16 [15] (N = 21).

Coloration in life: A photo of a recently collected specimen of S. cramptoni from the Rio Negro , Brazil, shows a whitish-pink fish with the dark chromatophores on the head appearing as very small dots.

Coloration in alcohol: Overall ground coloration ranging from brown to dark brown. Head and body with dark chromatophores relatively densely scattered over surfaces. Size of chromatophores and intensity of their pigmentation greater in overall darker specimens. Snout with variably distinct, narrow band of darker pigmentation extending anteriorly from region somewhat anterior of eye and reaching anterior portion of snout in many specimens. Band of dark pigmentation forms lateral border of narrow, lightly coloured mid-dorsal band on head. Ventral margin of snout somewhat darker than lateral surface of that region in some specimens, more so in individuals with overall dark coloration of head and body. Mid-dorsal region of head with narrow, lightly coloured stripe apparent even in overall darkly pigmented individuals. Head stripe continuous posteriorly with narrow, lightly coloured mid-dorsal stripe on body. Body pigmentation slightly darker dorsally, but with lightly pigmented mid-dorsal stripe extending posteriorly onto basal portions of electroreceptive filament and to varying degrees posteriorly from that point in different individuals.

Pectoral-fin coloration ranging from dusky to distinctly dark, with dark pigmentation overlying pectoral-fin rays and more developed distally. Anal fin with distinct band of dark pigmentation. Dark band covering approximately distal one-fifth to onehalf of fin in most examined specimens, but with dark coloration extending over all, or nearly all, of lateral surface of fin in some darkly coloured individuals. Caudal-fin rays ranging from slightly dusky to distinctly dark with extent and intensity of pigmentation greater in overall more darkly pigmented individuals.

Distribution: Sternarchorhynchus cramptoni is widely distributed along the mainstream of the Amazon River from the region of Iquitos in north-eastern Peru downstream to the Rio Trombetas , a left bank tributary of the Amazon in the state of Pará, Brazil ( Fig. 28 ).

Ecology: Juveniles of S. cramptoni have been captured along the margins of main river channels in várzea, whereas adults were captured in the main channels of the sampled rivers (C. D. de Santana, pers. observ.).

Electrical organ discharge: Crampton & Albert (2006: 689) reported that S. cramptoni (the Sternarchorhynchus n. sp. C of those authors and Crampton, 2007) has a complex EOD pattern comprising four phases of alternating polarities with the weak negative phase apparently flat, but on closer examination exhibiting a gentle curve around a single peak (the type F EOD of those authors). They also noted that the multiphasic nature of this EOD form diverts the energy of the signal away from the fundamental, with the first harmonic representing the peak power frequency.

Secondary sexual dimorphism: Examined samples of S. cramptoni demonstrated sexual dimorphism in the form of the lower jaw and associated dentition. Although males of the species have a somewhat enlarged anterior portion of the dentary, that region is not as relatively elongate or bulbous as in males of some congeners. Dentary dentition in that region is also proportionally less developed than are the teeth in mature males of many species of Sternarchorhynchus .

Etymology: The species name, cramptoni , is in recognition of the many contributions of William Crampton, University of Central Florida, to our knowledge of the biology and systematics of gymnotiforms.

Material examined

Holotype: – BRAZIL. Amazonas: Rio Solimões , downstream from mouth of Río Purus (3°27′27″S, 60°45′26″W); collected by Angela Zanata et al., 1.viii.1996; INPA 28376 (290, female; formerly FMNH 115489).

Paratypes: – BRAZIL. Amazonas: Rio Solimões , south bank of Ilha do Jaraqui, Alvarães (3°09.51’S, 64°48.76′W), collected by W. G. R. Crampton, 9.xii.1999; MCP 41637, 1 (236). Río Solimões , Ilha do Prego, opposite town of Alvarães (3°12.63’S 64°47.38′W); collected by W. G. R. Crampton, 19.ii.2001; MCP 41638, 1 (331). Rio Solimões , downstream from mouth of Rio Purus (3°27′27″S, 60°45′26″W); collected by Angela Zanata et al., 1.viii.1996, collected with holotype, FMNH 115489, 3 (155–273). Rio Solimões , downstream from mouth of Río Purus (3°26′46″S, 60°45′00″W); collected by Angela Zanata et al., 31.vii.1996; FMNH 115488, 4 (231–275). Rio Solimões , downstream from mouth of Rio Purus (3°27′22″S, 60°45′21″W); collected by Angela Zanata et al., 1.viii.1996; FMNH 115490, 7 (133–315).

Nontype specimens: – BRAZIL. Amazonas: Rio Solimões , between mouths of Rio Iça and Río Tonantins , between towns of São Antônio do Iça and Nova Tonantins (2°55′00″S, 67°50′48″W); FMNH 115483, 1 (222). Rio Solimões , between mouth of Rio Iça and Río Tonantins , between towns of São Antônio do Iça and Nova Tonantins (2°55′24″S, 67°51′23″W); FMNH 115482, 1 (280). Rio Amazonas, between mouth of Rio Madeira and Paraná do Serpa, between Manaus and Itacoatiara (3°19′44″S, 58°35′28″W); FMNH 115494, 1 (128). Rio Amazonas, downstream from mouth of Rio Madeira , upstream from Itacoatiara (3°20′22″S, 58°36′31″W); FMNH 115496, 1 (267). Rio Amazonas, upstream from mouth of Rio Madeira and upstream from Itacoatiara (3°15′42″S, 58°58′24″W); FMNH 115491, 2 (154–293). Río Amazonas, downstream from mouth of Río Madeira and upstream from Itacoatiara (3°20′09″S, 58°36′11″W); FMNH 115492, 1 (240). Rio Amazonas, downstream from mouth of Rio Madeira , upstream from Itacoatiara (3°20′59″S, 58°39′32″W); FMNH 115495, 1 (307). Rio Amazonas, between mouths of Rio Negro and Rio Madeira , between towns of Nova Oriente and Itacoatiara (3°16′40″S, 58°56′56″W); FMNH 115493, 1 (215). Rio Purus, Itapuru (4°17′S, 61°54′10″W); INPA 17098, 1 (180). Rio Solimões , Ilha da Marchantaria; INPA 27491 (255); INPA 27114, 1 (245). Rio Purus , marginal lago on shore opposite Lago Surara (4°07′47S, 61°34′50″W); INPA 17099, 1 (265). Rio Purus at Beruri; INPA 17602, 1 (380). Rio Purus, Baia da Resaca , at Beruri; INPA 17603, 2 (328–358). Rio Solimões , Ilha do Careiro; INPA 17601, 3 (327–334). Rio Solimões ; INPA uncat. 1 (166). Rio Solimões (3°36′19″S, 61°18′39″W); USNM 373328, 1 (163). Rio Solimões , below Purus (3°36′25″S 61°19′40″W); MZUSP 56882, 2 (150–164). Pará: Río Trombetas , between tributaries Lago Iripixi and Cachoeiri, between towns Oriximiná and Fazenda Paraíso; FMNH 115487, 1 (170).

PERU. Loreto: Iquitos, Río Amazonas , obtained from aquarium trade; UF 116761 , 4 (99–121), UF 123454 , 2 (167–310). Iquitos, Río Amazonas ; UF 116760 , 1 (241).

Figures

Figure 28. Map of central and northern South America showing geographical distribution of Sternarchorhynchus axelrodi sp. nov. (1 = holotype locality), Sternarchorhynchus britskii, Sternarchorhynchus caboclo, Sternarchorhynchus chaoi sp. nov. (2 = holotype locality), and Sternarchorhynchus cramptoni sp. nov. (3 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 32. Sternarchorhynchus cramptoni sp. nov., holotype, female, 290 mm total length, INPA 28376; Brazil, Amazonas, Rio Solimões, downstream from mouth of Rio Purus.

Figure 33. Sternarchorhynchus cramptoni sp. nov., sexually dimorphic male demonstrating modifications of dentary and dentary dentition, 331 mm total length, MCP 41638, demonstrating expanded sexually dimorphic dentary and associated dentition; Brazil, Amazonas, Rio Solimões, Ilha do Prego.