Sternarchorhynchus starksi, 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 : 344-346

STERNARCHORHYNCHUS STARKSI SP. NOV.

( FIGS 68 , 71 ; TABLE 13)

Sternarchorhynchus mormyrus , not of Steindachner, Eigenmann & Bean, 1907: 666 [ Brazil, lower Amazon between Pará (= Belém) and Manaus].

Sternarchorhynchus curvirostris , not of Boulenger, Starks, 1913: 23 [ Brazil, Pará (= fish market at Belém].

Diagnosis: Sternarchorhynchus starksi is distinguished from congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the anterior naris, the presence of a definite series of scales along the mid-dorsal region of the body, the lateral line extending posteriorly to the base of the caudal fin, 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 without a distal dark band, the extension of the dorsal filament posteriorly to a point along the vertical approximately eight scales posterior of the terminus of the base of the anal fin, the possession of ten to 13 premaxillary teeth, eight teeth on the outer row of the dentary, four to five teeth on the inner row of the dentary, 18–26 anterior unbranched anal-fin rays, 185–202 total anal-fin rays, 11–14 scales above the lateral line at the midbody, 11–13 caudal-fin rays, the greatest body depth (9.7– 12.5% of LEA), the head length (14.8–18.1% of LEA), the distance from the snout to the anus (7.0–10.8% of LEA), the distance from the anus to the anal-fin origin (8.3–18.3% of LEA), the prepelvic distance (14.4–18.3% of LEA), the caudal length (12.2–16.5% of LEA), the snout length (56.3–61.6% of HL), the distance from the posterior naris to the eye (47.8– 53.7% of HL), the pectoral-fin length (40.6–53.2% of HL), the head depth at the eye (26.9–36.2% of HL), the head depth at the nape (50.5–69.3% of HL), the head width (23.1–28.4% of HL), and the tail depth (9.9–13.2% of caudal length).

Description: Morphometric data for examined specimens in Table 13.

Lateral line extending posteriorly to base of caudal fin, but absent on fin. Snout elongate, compressed and slightly to distinctly curved ventrally; degree of curvature more pronounced in larger individuals. Mouth terminal and relatively small, with rictus located slightly anterior to vertical through anterior naris. Anus and urogenital papilla located ventral to head, with position apparently ontogenetically somewhat variable. Those structures situated along vertical approximately four orbital diameters posterior of rear margin of eye in smaller specimens and approaching, or along, vertical through eye in larger individuals. Combined opening for anus and urogenital papilla longitudinally ovoid.

Premaxilla with ten to 13 teeth (N = 9) apparent in whole specimens. Dentary with two tooth rows; outer row with eight teeth and inner row with four to five teeth (N = 6).

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

Pectoral-fin rays ii + 12–14 [ii + 13] (N = 13). Analfin origin located anterior to vertical through margin of opercle. Anterior unbranched anal-fin rays 18–26 [22] (N = 13). Total anal-fin rays 185–202 [199] (N = 11). Scales above lateral line at midbody 11–14 [11] (N = 13). Scales present along mid-dorsal line to origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located approximately at 56% of TL. Filament extending posteriorly to point eight to ten scales posterior of vertical through posterior terminus of base of anal fin. Tail compressed and long, ending in small, moderate, pointed caudal fin. Caudal-fin rays 11–13 (N = 7).

Morphometric values for paratypes of S. taphorni that are functions of length from tip of snout to end of anal fin and caudal length not available because of damage of tails. Number of specimens indicated in parentheses.

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

Coloration in alcohol: Overall coloration light brown. Head with narrow, faint stripe of slightly darker pigmentation extending anteriorly from orbit for distance half to two-thirds length of snout. Darker pigmentation on snout forms lateral margin of lightly coloured, mid-dorsal stripe on snout. Lightly coloured mid-dorsal stripe on snout expands into longitudinally elongate ovoid area above postocular portion of head. Ovoid region continuous posteriorly with barely apparent mid-dorsal, lightly coloured stripe that extends posteriorly from rear of head for varying degrees, but which falls short of origin of electroreceptive filament. Pectoral fin hyaline to dusky. Anal fin hyaline. Caudal fin slightly dusky.

Distribution: Samples of S. starksi with definite locality information originated in the easternmost portions of the Amazon basin or were purchased in the fish market at Belém ( Starks, 1913: 4, 23); cited therein as S. curvirostris ). Given the fishing and transportation technology of that era, it is likely that those market samples were captured close to that city in the lowermost portion of the Amazon River ( Fig. 68 ).

Secondary sexual dimorphism: No sexual dimorphism apparent in limited available samples of S. starksi .

Etymology: The species name, starksi , is in honour of Edwin Chapin Starks of Stanford University, who in the early part of the twentieth century collected a portion of the series that served as the basis for this description and who made a number of contributions to our knowledge of the anatomy of fishes.

Remarks: Examination of the specimens (CAS SU 22193; USNM 52542) that served, at least in part, as the basis for the citation of S. mormyrus from the lower Amazon between Pará (= Belém) and Manaus ( Eigenmann & Bean, 1907: 666) and of S. curvirostris from the Belém region ( Starks, 1913: 23) has shown them to be S. starksi .

Material examined

Holotype: – BRAZIL. Pará: Rio Pará between Rio Boa Vista and Rio Tocantins, between towns of Boa Vista and Abaetetuba (1°45′30″S, 49°29′17″W), collected by A. M. Zanata et al., 18.xi.1994; INPA 28377 (231, formerly FMNH 115485).

Paratypes: – BRAZIL. Pará: Pará (= fish market at Belém), collected by E. C. Starks, 1911; CAS SU 22193, 10 (203–374). Rio Amazonas between Pará (= Belém) to Manaus, collected by J. B. Steere, 1901; USNM 52542, 2 [229 (tail broken)-267]. Río Jari, Monte Dourado , upstream of Rio Amazonas, L. Py-Daniel et al., 13.xi.1994; MZUSP 58196, 1 (260).

Nontype specimens: – BRAZIL. Pará: Rio Amazonas, above Rio Xingu and town of Gurupá (1°28′38″S, 52°04′00″W), USNM 373029, 1 (278 regenerated tail). Pará (= fish market at Belém); AMNH 3776, 1 (307), AMNH 9869, 1 (259).

Figures

Figure 68. Map of central and northern South America showing geographical distribution of Sternarchorhynchus roseni, Sternarchorhynchus schwassmanni sp. nov. (1 = holotype locality), Sternarchorhynchus severii, and Sternarchorhynchus starksi sp. nov. (2 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 71. Sternarchorhynchus starksi sp. nov., holotype, 231 mm total length, INPA 28377; Brazil, Pará, Rio Pará.