Sternarchorhynchus hagedornae, 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 : 305-307

STERNARCHORHYNCHUS HAGEDORNAE SP. NOV.

( FIGS 42–44 ; TABLE 7)

Sternarchorhynchus sp. , Ortega, 1996: 469 [ Peru, Manu Biosphere Reserve , Rio Manu and Quebrada de Pachija , tributary to Rio Manu ]. – Hagedorn & Keller, 1996: 493, fig. 2f [ Peru, Manu Biosphere Reserve, Quebrada de Pachija , tributary to Rio Manu ; habitat, EOD, secondary sexual dimorphism].

Diagnosis: Sternarchorhynchus hagedornae 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 distinctly longitudinally elongate combined opening for the anus and the urogenital opening, the sparse scales covered by skin along the mid-dorsal portion of the body anterior to the origin of the electroreceptive filament, the consistently dark overall coloration of the head and 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 posterior of that point, the absence of a very dark band of pigmentation at the base of the enlarged patch of dentition on the dentary in mature males, the possession of five to six teeth in the outer tooth row of the dentary, 27–35 anterior unbranched anal-fin rays, 173–193 total anal-fin rays, nine to 13 scales above the lateral line at the midbody, the greatest body depth (11.4–13.3% of LEA), the length of the anal-fin base (86.6–89.6% of LEA), the prepectoral-fin distance (17.6–20.8% of LEA), the caudal length (5.5–8.3% of LEA), the head depth at the nape (53.1–59.2% of HL), the head width (24.1– 28.3% of HL), the distance from the posterior naris to the snout (8.7–9.8% of HL), the mouth length (6.4– 8.6% of HL), the interocular width (6.0–8.5% of HL), the distance from the posterior naris to the eye (44.6– 48.9% of HL), the postocular distance (43.6–46.2% of HL), the pectoral-fin length (39.1–46.9% of HL), and the tail depth (21.3–30.4% of caudal length).

Description: Morphometric data for holotype and paratypes in Table 7.

Lateral line extending to base of caudal fin, but absent on fin. Snout elongate, compressed and straight. Posterior naris closer to tip of snout than to anterior margin of orbit. Branchial opening restricted and situated slightly anterior to vertical through pectoral-fin origin. Location of anus and urogenital papilla apparently ontogenetically and perhaps sexually variable, but definite pattern uncertain because of limited sample size. Anus and urogenital papilla in smaller individual (162 mm TL) located at vertical running two orbital diameters posterior of eye. Midsized specimen (206 mm SL) with structures positioned slightly anterior of vertical through eye. Male with definite patch of enlarged dentition on expanded anterior portion of dentary (249 mm TL) with anus and urogenital papilla more anteriorly positioned, and located along vertical approximately one-quarter of distance between anterior limit of orbit and tip of snout. Combined opening for anus and urogenital papilla longitudinally elongate.

Premaxilla of small size, somewhat rounded, with five to eight teeth (N = 4). Dentary with two tooth rows. Outer tooth row with five to six curved conical teeth and inner tooth row with three to four teeth (N = 3). Mature males with dentary expanded anteriorly and widened laterally into dorsally bulbous region rounded from dorsal view, with expansion bearing patch of enlarged dentition. Mouth terminal with rictus in juveniles located slightly posterior to vertical through anterior naris. Rictus in adults shifted somewhat anteriorly and located anterior to vertical through anterior naris.

Branchiostegal rays five; with first to third rays relatively narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 16–17 (13 anterior; three to four transitional; N = 4).

Pectoral-fin rays ii + 12–14 [ii + 14] (N = 6). Anal-fin origin located slightly posterior of vertical through anterior margin of opercle. Anterior unbranched analfin rays 27–35 [27] (N = 6). Total anal-fin rays 173– 193 [173] (N = 6). Scales above lateral line at midbody nine to 13 [13] (N = 6). Scales along mid-dorsal region of body somewhat sparse and not readily apparent on body surface. Origin of midsaggital electroreceptive filament located approximately at 70% of TL. Filament in juveniles extending posteriorly to vertical one scale posterior of vertical through posterior terminus of base of anal fin; filament in adults reaching to vertical through posterior terminus of base of anal fin. Tail compressed and short, ending in small and moderate caudal fin. Caudal-fin rays 12–16 [18] (N = 6).

Coloration in alcohol: Overall ground coloration dark brown. Series of whitish, papillae-like structures broadly distributed over lateral and dorsal portions of posterior two-thirds of snout, lateral surface of head, and dorsalmost portion of body. Lightly coloured spots limited to irregular single series to each side of electroreceptive filament on posterior portion of body. Snout with variably distinct, narrow band of darker pigmentation extending anteriorly from region somewhat anterior of orbit; and reaching anterior portion of snout in some individuals and apparent even in overall darkly pigmented specimens. Band of dark pigmentation forms lateral border of narrow, more lightly coloured mid-dorsal band present on head. Anterior portion of lightly coloured mid-dorsal stripe on head less apparent in male with well-developed patches of enlarged dentition on lower jaw. Body pigmentation very slightly darker dorsally, but with mid-dorsal more lightly coloured stripe continuous with corresponding stripe on head and extending posteriorly onto basal portions of electroreceptive filament.

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

Distribution: All examined specimens of S. hagedornae originated in the Manu Biosphere Reserve , in the upper Río Madeira basin in south-eastern Peru ( Fig. 42 ).

Ecology: Hagedorn & Keller (1996: 488, 490 493) remarked that the type locality for S. hagedornae, Quebrada Pachija , is an open-gallery, high flow stream with a flow of 0.748 m /s, a mean stream depth of 0.397 ± 0.059 m, and a mean stream width of 19.1 ± 1.0 m. According to these authors this species, (their Sternarchorhynchus sp. ) ‘lived in the fastest flowing water sampled; most adult specimens were captured from a single rocky rapids’. Their collecting efforts also yielded numerous fry and small juveniles from within floating debris along the fast-flowing edges of the Río Manu that they considered to be the same species. We have not examined these samples.

Electrical organ discharge: Sternarchorhynchus hagedornae was studied in the field by Hagedorn & Keller (1996: 493, figs 2f, 4) who reported that it is a high frequency, wave-type fish with peak-power EOD frequencies ranging from 977–2832 Hz and a mean of 1608.5 ± 160.6 Hz SE in the 14 specimens examined. They remarked on the variety of EOD types observed in the species ( Hagedorn & Keller, 1996: fig. 4), but pointed out that they lacked sufficient specimens to determine whether this variation reflected sexual dimorphism in this feature; however, they did comment that the heterogeneity might reflect changes with ‘age, sex and/or activity pattern’.

Secondary sexual dimorphism: The obvious sexually dimorphic feature in S. hagedornae is the anteriorly lengthened and transversely widened anterior portion of the dentary in males and the associated patch of enlarged, posteriorly recurved teeth on this region. The male (249 mm TL) had the anus and urogenital papilla more anteriorly positioned than did the slightly shorter, possibly female, specimen (206 mm TL) and the juveniles. In the male, the anus and the urogenital papilla are located along the vertical running approximately one-quarter of the distance between the anterior limit of the orbit and the tip of the snout. This position is distinctly anterior of the location of the anus and urogenital papilla in smaller specimens, in which these structures are positioned from slightly anterior to variably posterior of the vertical through the eye.

Etymology: The species name, hagedornae , is in honour of Mary Hagedorn of the Smithsonian Institution who collected the type series and has made many contributions to our understanding of the diversity of gymnotiforms.

Material examined

Holotype: – PERU. Madre de Dios: Manu Biosphere Reserve, Quebrada Pachija , tributary emptying into Río Manu 3 km upstream of Pakitza (Pakitza at 11°55′48″S, 71°15′18″W), MUSM 30534, 1 (249, male); collected by M. Hagedorn et al.

Paratypes: – PERU. Madre de Dios: Manu Biosphere Reserve, Quebrada Pachija , tributary emptying into Río Manu 3 km upstream of Pakitza (Pakitza at 11°55′48″S, 71°15′18″W), collected by M. Hagedorn et al., with holotype, USNM 391574, 2 (169–206); MUSM 30535, 1 (202); MBUCV 33742, 2 (162–194). MUSM 23755, (174); Manu Biosphere Reserve , Río Los Amigos.

Nontype specimens: – PERU. Cuzco: Río Inambari and mouth of Quebrada Hondonado , Madre de Dios drainage, upstream of Puerto Mazuko (13°06′23″S, 70°24′44″W), ANSP 180637, 2 (200–208) .

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 43. Sternarchorhynchus hagedornae sp. nov., holotype, sexually dimorphic male demonstrating modifica- tions of dentary and dentary dentition, 249 mm total length, MUSM 30534; Peru, Madre de Dios, Río Manu.

Figure 44. Sternarchorhynchus hagedornae sp. nov., female, approximately 192 mm total length, ANSP 180637; Peru, Madre de Dios, Quebrada Pachija, Río Manu.