Sternarchorhynchus curumim, DE SANTANA & CRAMPTON, 2006

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 : 291-296

STERNARCHORHYNCHUS CURUMIM DE SANTANA & CRAMPTON ( FIGS 34 , 35 ; TABLE 5)

Sternarchorhynchus curumim de Santana & Crampton, 2006: 59 , fig. 1 [type locality: Brazil, Amazonas, Rio Tefé, Toco Preto, Municipality of Tefé, 3°47.31′S, 64°59.91′W]. – Crampton, 2007: 289, 297 [western Amazon; occurrence in blackwater but not whitewater habitats].

Diagnosis: Sternarchorhynchus curumim 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 absence 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, the lateral line that extends to the base of the caudal fin, the dusky anal fin without a distinct dark band along its distal margin, the possession of seven to ten teeth on the premaxillary, seven to eight teeth in the outer row of the dentary, 15 precaudal vertebrae, 23–24 anterior unbranched anal-fin rays, 179–189 total anal-fin rays, ten to 11 scales above the lateral line at the midbody, 13–15 caudal-fin rays, the greatest body depth (9.0–10.0% of LEA), the distance from the anus to the anal-fin insertion (8.3–13.5% of HL), the preanal distance (12.4–14.4% of LEA), the caudal length (10.9–12.2% of LEA), the head length (18.7– 20.6% of LEA), the snout length (60.2–62.5% of HL), the mouth length (3.5–5.6% of HL), the eye diameter (4.1–5.0% of HL), the internarial distance (2.4– 2.8% of HL), the postocular distance (33.6–39.2% of HL), the pectoral-fin length (34.5–37.8% of HL), the tail depth (10.6–11.9% of caudal length), and the caudal length (10.9–12.2% of LEA).

Description: Morphometric data for examined specimens in Table 5.

Lateral line extending posteriorly to point approximately at base of caudal fin but absent on fin. Snout elongate, compressed and slightly curved ventrally distally. Mouth terminal and relatively small, with rictus located slightly posterior of vertical through anterior naris. Anus and urogenital papilla located ventral to head, with position apparently sexually dimorphic in limited available sample of species. Anus and urogenital papilla positioned along vertical situated approximately one orbital diameter posterior of rear margin of eye in single examined mature female and positioned at vertical one orbital diameter anterior of eye in single mature male. Combined opening for anus and urogenital papilla ovoid in one examined mature male and somewhat more horizontally elongate in mature female.

Premaxilla with seven to ten teeth (N = 3) apparent in whole specimens. Dentary with two rows of conical teeth; outer row with seven to eight teeth and inner row with three to four teeth (N = 2).

Branchiostegal rays five; with first three rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 15 (12 anterior; three transitional; N = 4).

Pectoral-fin rays ii + 11–12 [ii + 12] (N = 4). Anal-fin origin located anterior to vertical through margin of opercle. Anterior unbranched anal-fin rays 23–24 (N = 2). Total anal-fin rays 179–189 [189] (N = 3). Scales above lateral line at midbody ten to 11 [10] (N = 4). Scales clearly present along mid-dorsal line to origin of midsaggital electroreceptive filament. Origin of midsaggital electroreceptive filament located relatively far posteriorly, approximately at 60% of TL. Filament extending posteriorly to vertical located approximately three scales posterior of vertical through terminus of base of anal fin. Tail compressed and moderate, ending in small, elongate caudal fin. Caudal-fin rays 13–15 [15] (N = 3).

Coloration in alcohol: Overall coloration of head and body dark brown. Snout dark overall with stripe of slightly darker pigmentation extending anteriorly from orbit to, or nearly to, tip of snout. Pectoral fin distinctly dusky with rays covered with small dark chromatophores. Anal fin dusky with rays overlain by dark chromatophores. Basal portions of caudal fin distinctly dark, but with distal portions of fin hyaline.

Distribution: Sternarchorhynchus curumim is only known from one locality in the Rio Tefé in the state of Amazonas, Brazil ( Fig. 35 ).

Secondary sexual dimorphism: As documented by de Santana & Crampton (2006: 1166), the single mature male of S. curumim has the posterior region of the snout distinctly more developed vertically than do the three known females. No other sexually dimorphic features are present other than for the relatively minor difference in the positions of the anus and urogenital papilla described above.

Material examined

BRAZIL. Amazonas : Rio Tefé, Toco Preto, Município de Tefé (3°47.31′S, 64°59.91′W); MCP 38304, 1 (holotype; female, 163 mm); MCP 38305, 2 (paratypes: female 211 mm, male 183 mm); INPA 25256, 1 (cleared and stained paratype; female, 181 mm) .

STERNARCHORHYNCHUS CURVIROSTRIS (BOULENGER)

( FIGS 35 , 36 , 37 ; TABLE 6)

Sternarchus (Rhamphosternarchus) curvirostris Boulenger, 1887: 282 , pl. 24 [type locality; Ecuador, Canelos]. – Eigenmann & Eigenmann, 1891: 62 [assignment to Sternarchorhynchus ]. – Ellis, 1913: 141 [ Sternarchorhynchus curvirostris placed in synonymy of S. oxyrhynchus ]. – Fernández-Yépez, 1967: 18 [ Sternarchorhynchus curvirostris resurrected from synonymy of S. oxyrhynchus ]

Sternarchorhynchus curvirostris, Eigenmann & Bean, 1907: 666 [ S. curvirostris as possible synonym of S. mormyrus ]. – Fernández-Yépez, 1967: 18 [ S. curvirostris resurrected from synonymy of S. oxyrhynchus ]. – Mago-Leccia, 1994: 37, fig. 55 [as valid species in listing of members of genus]. – Campos-da- Paz, 2000: 528, fig. 3 [in key to species of Sternarchorhynchus ; syntype illustrated]. – Albert, 2003: 500 [in listing of members of genus].

Diagnosis: Sternarchorhynchus curvirostris 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 lateral line that extends 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 sometimes the mid-dorsal region of the body anterior of the origin of the electroreceptive filament, the darkly coloured anal fin with darker basal coloration but without a distinct, dark, distal band, the presence of eight to 11 teeth on the premaxilla, six teeth in the outer row of the premaxilla, four teeth on the inner row of the premaxilla, 25 unbranched anal-fin rays, 173–180 total anal-fin rays, 16 precaudal vertebrae, 15–16 caudal-fin rays, the preanal distance (11.3–13.4% of LEA), the greatest body depth (12.5–15.0% of LEA), the caudal length (7.9–10.4% of LEA), the distance from the anus to the anal-fin insertion (6.0–6.8% of HL), the head depth at the eye (27.2–35.4% of HL), the head depth at the nape (50.9–67.3% of HL), the snout length (64.5–66.1% of HL), the distance from the posterior naris to the snout (6.9–7.4% of HL), the internarial distance (3.0–4.5% of HL), the eye diameter (3.6–5.8% of HL), the interocular distance (5.6–6.8% of HL), the postocular length (36.7–40.3% of HL), the height of the branchial opening (13.8–16.6% of HL), the pectoral-fin length (38.5–45.7% of HL), and the tail depth (12.7–17.5% of caudal length).

Description: Morphometric data for examined specimens in Table 6.

Lateral line extending posteriorly to base of caudal fin, but absent on fin. Snout elongate, compressed and distinctly curved ventrally. Mouth terminal and relatively small, with rictus located anterior to vertical through posterior naris. Anus and urogenital papilla located ventral to head, situated along vertical through eye. Combined opening for anus and urogenital papilla ovoid, with intraspecific proportional variation in width of opening.

Premaxilla with eight to 11 teeth (N = 2) apparent in whole specimen. Dentary with two tooth rows; outer row with six teeth and inner row with four teeth (N = 2).

Number of specimens indicated in parentheses. H, holotype; range includes nontype specimens.

Branchiostegal rays five; with first three rays narrow and elongate and fourth and fifth rays large and broad. Precaudal vertebrae 16 (13 anterior; three transitional; N = 1).

Pectoral-fin rays ii + 11–14 [ii + 11] (N = 5). Anal-fin origin located anterior to opercle. Anterior unbranched anal-fin rays 25 (N = 1). Total anal-fin rays 173–180 [180] (N = 4). Scales above lateral line at midbody nine to 11 [10] (N = 5). Scales present along mid-dorsal line to origin of electroreceptive filament. Origin of midsaggital electroreceptive filament located approximately at 59% of TL. Filament extending posteriorly to vertical through posterior terminus of base of anal fin. Tail compressed and short, ending in small, elongate, pointed caudal fin. Caudal-fin rays 15–16 (N = 3).

Coloration in alcohol: Available specimens including syntypes variably depigmented. Overall coloration tan to brown, but missing on some regions in some nontype specimens as consequence of apparent postmortem damage. Head slightly lighter midventrally and with narrow, lightly coloured mid-dorsal stripe that commences midway along length of snout and expands laterally in region above orbit into longitudinally ovoid, more lightly pigmented area on dorsal surface of postocular portion of head. Lightly coloured region terminates posteriorly approximately at vertical through anterior margin of opercle. Stripe obscure in some individuals. Body tan to dark overall and lacking distinct, narrow, lightly coloured mid-dorsal stripe present in some congeners. Pectoral fin dusky to dark. Anal fin nearly hyaline to dark, more so basally. Caudal fin dusky to dark.

Distribution: Sternarchorhynchus curvirostris is known from the Río Bobanaza , eastern Ecuador and perhaps from north-eastern Peru ( Fig. 35 ; under Remarks below).

Remarks: The original description of Sternarchus (Rhamphosternarchus) curvirostris by Boulenger (1887: 282) reported the length as 125 mm TL. The two specimens now identified as the syntype series (BMNH 1880.12.890-891) are, however, distinctly longer than that length [note: Mago-Leccia (1994: fig. 55) and Campos-da-Paz (2000: fig. 3) both labelled a specimen as the ‘type’, whereas there are two syntypes]. Searches through the collections of the BMNH failed to yield any other specimens of S. curvirostris that correspond to the length reported in the species description. It is impossible to determine whether the reported original length was a lapsus or the purported types are not the material on which the species was based. This question notwithstanding, the specimens identified as the syntypes of Sternarchus curvirostris (= Sternarchorhynchus curvirostris ) otherwise conform to the details in the original description of that species.

Eigenmann & Bean (1907: 666) proposed that S. curvirostris might be a synonym of S. mormyrus on the basis of specimens that originated in the lower Amazon River between Manaus and Pará (= Belém). They believed that those eastern Amazonian specimens bridged the differences in morphometrics and meristics purported to differentiate S. curvirostris from S. mormyrus . Sternarchorhynchus curvirostris along with S. mormyrus were, in turn, considered to be junior synonyms of S. oxyrhynchus by Ellis (1913: 141), who recognized the latter species as a monotypic, morphologically highly variable form.

Fernández-Yépez (1967: 18) resurrected S. curvirostris (and S. mormyrus ) from the synonymy of S. oxyrhynchus on the basis of external features of the head. The recognition of S. curvirostris as a distinct species continued with Mago-Leccia (1994: 37), Campos-da-Paz (2000: 528), and other authors. Based on the information provided by Fernández-Yépez (1967), the specimens that he considered to be S. mormyrus were misidentified and it is highly questionable whether the specimen he identified as S. curvirostris was that species. Notwithstanding the fact that Fernández-Yépez based his conclusions on erroneous information, our results confirm that S. curvirostris is a distinct species. Various authors followed Fernández-Yépez (1967) in considering S. curvirostris a component of the Venezuelan ichthyofauna, but we have not examined any specimens of the species that originated in that country or regions proximate to it. It is likely that the original citation represents a misidentification.

We located only five specimens of S. curvirostris in museum collections, the two apparent syntypes (BMNH 1880.12.8.90-91) and three other specimens (MCZ 48676; USNM 163887) that were also collected in the Río Bobonaza , Ecuador, the river system from which the type series originated. Three other specimens from portions of north-eastern Peru proximate to the type region (LACM 36324-2, LACM 36327-3) would be considered conspecific with S. curvirostris based on counts and overall form of the head and body, but differ from Ecuadorian samples in the degree of pigmentation on the snout. Although this difference may be a consequence of differential preservation or geographical variation, we defer from formally equating these specimens with S. curvirostris at this time.

Secondary sexual dimorphism: Sternarchorhynchus curvirostris is not known to demonstrate sexual dimorphism.

Material examined

ECUADOR. Pastaza: Canelos (1°35′S, 77°45′W); BMNH 1880.12.8.90-91, 2 (length undetermined because of missing tail-203.2; syntypes of Sternarchorhynchus (Rhamphosternarchus) curvirostris ; See remarks concerning the reported type status of these specimens). Río Putuno , tributary of Río Bobonaza ; MCZ 48676, 1 (235). Upper Río Pastaza basin, Río Bobonaza, Chicirota (2°22′S, 76°38′W), USNM 163887, 2 (217–240).

The following specimens may be S. curvirostris (see Remarks above).

PERU. Amazonas: Río Santiago at La Poza (4°01′S, 75°18W); LACM 36324-2, 1 (189), LACM 36327-3, 2 (150–238) .

Figures

Figure 34. Sternarchorhynchus curumim, paratype, female, 211 mm total length, MCP 38305; Brazil, Amazonas, Río Tefé.

Figure 35. Map of central and northern South America showing geographical distribution of Sternarchorhynchus curumim, Sternarchorhynchus curvirostris, Sternarchorhynchus freemani sp. nov. (1 = holotype locality), Sternarchorhynchus galibi sp. nov. (2 = holotype locality), and Sternarchorhynchus gnomus (some symbols represent more than one locality and/or lot of specimens).

Figure 36. Sternarchorhynchus curvirostris, illustration of syntype from Boulenger (1887).

Figure 37. Sternarchorhynchus curvirostris, female, 235 mm total length, MCZ 46676; Ecuador, Pastaza, Río Putuno.