Sternarchorhynchus mareikeae, 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 : 317-318

STERNARCHORHYNCHUS MAREIKEAE SP. NOV.

( FIGS 50 , 53 , 54 ; TABLE 9)

Sternarchorhynchus oxyrhynchus, Ferreira, 1995: 51 [in listing of species from Brazil, Rio Trombetas , Pará, Cachoeira Porteira].

Diagnosis: Sternarchorhynchus mareikeae is distinguished from congeners by the following combination of characters: a short gape that terminates posteriorly at, or slightly short of, the vertical through the anterior nares, the lateral line that extends posteriorly to the base of caudal fin, the presence of a definite series of scales along the mid-dorsal region of the body, the presence of a narrow, more lightly coloured middorsal stripe on the head with the stripe sometimes extending posteriorly along the body to the vertical through the insertion of the pectoral fin, the dark anal fin, the possession of 12–13 teeth in the outer row of the dentary, 12–13 teeth in the outer row of the dentary with a total of 16–17 teeth on that jaw, 159–181 total anal-fin rays, nine to 11 scales above the lateral line at the midbody, 16 precaudal vertebrae, the distance from the snout to the anus in mature males (8.8–10.8% of LEA), the preanal distance (12.2–17.8% of LEA; 12.2–15.2% in mature males), the caudal length (13.4–17.4% of LEA), the head length (18.3–23.2% of LEA), the prepectoral-fin distance (17.9–23.1% of LEA), the postocular distance (36.0–41.3% of HL), the pectoral-fin length (35.0– 40.9% of HL; 37.5–40.9% in mature males), the head depth at the eye in mature males (29.9–38.4% of HL), the head depth at the nape (45.1–53.4% of HL), the distance from the posterior naris to the eye in mature males (52.3–53.7% of HL), the eye diameter (3.5–5.3% of HL), the interocular width (6.6–9.0% of HL), the postocular distance (36.0–41.3% of HL), the height of the branchial opening in mature males (12.3–15.4% of HL), the tail depth (7.1–10.2% of caudal length), and the caudal-fin length (18.5–24.7% of caudal length).

Description: Morphometric data for examined specimens in Table 9.

Lateral line extending posteriorly to 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 and along vertical about three orbital diameters anterior of eye in both mature males and females. Combined opening for anus and urogenital papilla longitudinally ovoid in all specimens.

Premaxilla with 12–13 teeth (N = 7) apparent in whole specimens. Dentary with two tooth rows; outer row with 12–13 teeth and inner row with three to four teeth (N = 5).

Branchiostegal rays five; with first to third rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 16 (12 anterior; four transitional; N = 9).

Pectoral-fin rays ii + 10–12 [ii + 12] (N = 10). Analfin origin located anterior to opercle. Anterior unbranched anal-fin rays 15–26 [23] (N = 8). Total anal-fin rays 159–181 [170] (N = 10). Scales above lateral line at midbody nine to 11 [9] (N = 10). 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 four to seven scales beyond vertical through posterior terminus of base of anal fin. Tail compressed and moderate, ending in small, elongate, pointed caudal fin. Caudal-fin rays 12–14 (N = 6).

Coloration in alcohol: Overall coloration brown. Head dark brown overall laterally other than for more lightly coloured stripe extending along lateral surface of snout. Darker coloration anterior of eye along dorsal surface of snout forms lateral margin of very narrow, lightly coloured mid-dorsal stripe along snout that terminates in rear portion of head. 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.

Distribution: Sternarchorhynchus mareikeae is only known from the type locality at Cachoeira Porteira along the Rio Mapuera , Pará, Brazil ( Fig. 50 ).

Secondary sexual dimorphism: Sternarchorhynchus mareikeae is possibly sexually dimorphic in terms of body size. Mature females(N = 5) reach a maximum of 160 mm TL, whereas mature males collected with those specimens attain a maximum of 221 mm TL. This species matures at relatively small body sizes as indicated by a 131 mm TL female filled with welldeveloped eggs and a 176 mm TL male with mature testes.

Etymology: The species name, mareikeae , is in honour of the German biologist Mareike Roeder who has greatly added to the senior author’s life.

Remarks: Examination of the specimens cited from Cachoeira Porteira as S. oxyrhynchus by Ferreira (1995: 51) has shown that some are rather S. mareikeae . Sternarchorhynchus mareikeae occurs in the same river basin as S. inpai and the two species have similar coloration patterns. They differ both in the numbers of teeth in the upper and lower jaws and also in the various features involving mature males that were cited in the Diagnosis and summarized under Remarks for S. inpai .

Material examined

Holotype: – BRAZIL. Pará: Rio Trombetas, 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 22896, 192.0 mm TL, male.

Paratypes: – BRAZIL. Pará: Rio Trombetas, 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 22901, 9 (60–120, one specimen cleared and stained); INPA 22900, 3 (125– 148); USNM 391717, 1 (177).

Figures

Figure 50. Map of central and northern South America showing geographical distribution of Sternarchorhynchus jaimei (1 = holotype locality), Sternarchorhynchus kokraimoro sp. nov. (2 = holotype locality), Sternarchorhynchus mareikeae sp. nov. (3 = holotype locality), Sternarchorhynchus marreroi sp. nov. (4 = holotype locality), and Sternarchorhynchus mendesi sp. nov. (5 = holotype locality) (some symbols represent more than one locality and/or lot of specimens).

Figure 53. Sternarchorhynchus mareikeae sp. nov., holotype, male, 192 mm total length, INPA 22896; Brazil, Pará, Cachoeira Porteira, Rio Mapuera.

Figure 54. Sternarchorhynchus mareikeae sp. nov., paratype, female, 135 mm total length, INPA 22901; Brazil, Pará, Cachoeira Porteira, Rio Mapuera.