Sternarchorhynchus inpai, 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 : 310-312

STERNARCHORHYNCHUS INPAI SP. NOV.

( FIGS 42 , 47 , 48 ; TABLE 8)

Sternarchorhynchus oxyrhynchus Ferreira, 1995: 51 [ Brazil, Pará, Rio Trombetas, Cachoeira Porteira ].

Diagnosis: Sternarchorhynchus inpai is distinguished from all congeners by having a very short first branchiostegal ray that is distinctly shorter than the second ray rather than being approximately subequal in length to that ossification. It is furthermore differentiated from all other species of Sternarchorhynchus by possessing 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 middorsal region of the body, the more lightly coloured mid-dorsal stripe on the head sometimes extending posteriorly to the vertical through the insertion of the pectoral fin, the dusky anal fin, the very short first branchiostegal ray, the possession of four to seven premaxillary teeth, five to six teeth in the outer row of the dentary, 15 precaudal vertebrae, the distance from the snout to the anus in mature males (13.4% of LEA), the preanal distance (15.2–16.3% of LEA; 18.9 in mature male), the caudal length (12.6–15.6% of LEA), the pectoral-fin length (27.9–42.3% of HL; 27.9 in mature male), the head depth at the eye in mature males (26.3 of HL), the head depth at the nape (40.5–48.6% of HL), the distance from the posterior naris to the eye in mature males (59.7 of HL), the postocular distance (33.1–41.1% of HL), the height of the branchial opening (9.4–13.4% of SL; 10.9% in mature males), the tail depth (8.0–11.1% of caudal length), and the caudal-fin length (20.1–23.9% of caudal length).

Description: Morphometric data for examined specimens in Table 8.

Lateral line extending posteriorly to point four scales anterior of base of caudal fin but absent on fin. Snout elongate, compressed and slightly curved ventrally along anterior portion. Mouth terminal to very slightly anterodorsally orientated and relatively small with distinct fleshy pad at anterior of lower jaw. Rictus located anterior to vertical through anterior naris. Anus and urogenital papilla located ventral to head, with position apparently ontogenetically variable. Anus and urogenital papilla located along vertical about one orbital diameter posterior of eye in juveniles and along verticals through to one orbital diameter anterior of eye in mature males and females. Combined opening for anus and urogenital papilla longitudinally ovoid in all specimens.

Premaxilla with four to seven teeth (N = 6) apparent in whole specimens. Dentary with two tooth rows; outer row with five to six teeth and inner row with three teeth (N = 4).

Branchiostegal rays five; with first ray distinctly shorter than second and first three rays narrow. Fourth and fifth rays large and broad with fifth ray branched distally on both sides in cleared and stained specimen. Precaudal vertebrae 15 (13 anterior; two transitional; N = 6).

Pectoral-fin rays ii + 12–13 (N = 7). Anal-fin origin located anterior to opercle. Anterior unbranched analfin rays 17–24 [17] (N = 3). Total anal-fin rays 156– 167 [161] (N = 7). Scales above lateral line at midbody eight to 11 (N = 9). Scales present along mid-dorsal line to origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located on posterior half of body, approximately at 60% of TL. Filament extending posteriorly three to seven scales beyond vertical through posterior terminus of base of anal fin. Tail compressed and moderate, ending in small, elongate, pointed caudal fin. Caudalfin rays 13–16 [14] (N = 6).

Coloration in alcohol: Overall coloration brown. Head dark brown overall other than for more lightly coloured stripe along lateral surface of snout and very narrow, lightly coloured mid-dorsal stripe on snout that terminates posteriorly approximately at vertical through eye. Body dark overall, somewhat more so dorsally. Pectoral fin dusky with rays somewhat darker than membranes. Anal fin dusky with rays darker than membranes. Caudal fin dark with distal regions somewhat lighter.

Distribution: Sternarchorhynchus inpai is only known from the type locality at Cachoeira Porteira on the Rio Mapuera , Pará, Brazil ( Fig. 42 ).

Secondary sexual dimorphism: The single mature examined male of S. inpai as evidenced by the welldeveloped testes has a slightly longer snout than do females of comparable sizes. This species matures at relatively small body sizes with a 154 mm TL female bearing well-developed eggs and the single mature male being at least 222 mm (a portion of the caudal is lacking in this specimen).

Etymology: The species name, inpai , is in reference to the Instituto Nacional de Pesquisas da Amazônia (INPA), in Manaus, Brazil, that has been the centre for the study of the biodiversity of the Brazilian Amazon for over five decades.

Remarks: Specimens reported as S. oxyrhynchus by Ferreira (1995: 51) from Cachoeira Porteira have proved to be S. inpai . Sternarchorhynchus inpai occurs in the same river basin as S. mareikeae and the two species have similar coloration patterns. They differ in the numbers of teeth on the premaxilla (four to seven versus 12–13, respectively), and in the outer row of the dentary (five to six versus 12–13, respectively), and the number of precaudal vertebrae (15 versus 16, respectively). Mature males of the two species can be furthermore distinguished on various sexually dimorphic morphometric features detailed in tables 15 and 18 of Ferreira (1995), most notably the distance from the snout to the anus (13.4% in S. inpai versus 8.8–10.8% in S. mareikeae ), the preanal distance (18.9 versus 12.7–15.2%, respectively), and the height of the branchial opening (10.9 versus 12.3– 15.4%, respectively).

Material examined

Holotype: – BRAZIL. Pará: Rio Mapuera, Cachoeira Porteira , last fall before Rio Trombetas (approximately 1°05′S 57°02′W); collected by E. Ferreira and M. Jégu, 19.iv.1985; INPA 22895, 191.0 mm TL, female.

Paratypes: – BRAZIL. Pará: Rio Mapuera, Cachoeira Porteira , last fall before Rio Trombetas (approximately 1°05′S 57°02′W); collected with holotype by E. Ferreira and M. Jégu, 19.iv.1985; INPA 22899, 10 (1 CS; 54–222); USNM 391715, 1 (195).

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 47. Sternarchorhynchus inpai sp. nov., holotype, female, 191 mm total length, INPA 22895; Brazil, Pará, Cachoeira Porteira, Rio Mapuera.

Figure 48. Sternarchorhynchus inpai sp. nov., paratype, male (tail broken), 222 mm total length, INPA 22899; Brazil, Pará, Cachoeira Porteira, Rio Mapuera.