Steindachnerina binotata (Pearson 1924)

Steindachnerina binotata (Pearson, 1924)

Curimatus binotatus Pearson, 1924:28, pl. 19, fig. 1 [type locality: Bolivia: Rurrenbaque].—1937:109 [Río Beni drainage system].—Vari, 1989a, tables 2, 3 [assignment to Steindachnerina].

Curimata binotata.—Fowler. 1940b:98 [reference].—1950:279, fig. 377 [literature compilation].—Terrasas-Urquidi, 1970:30 [reference].

Cruxentina binotata.—Fernández-Yépez, 1948:53 [assignment to Cruxentina].—Fowler, 1975:367 [reference].

DIAGNOSIS.—The presence of three longitudinal, weakly developed folds on the roof of the oral cavity rather than three fleshy flaps and/or one or more series of lobulate fleshy processes in that region discriminates Steindachnerina binotata from its congeners with the exception of S. leucisca, S. argentea, S. conspersa, and S. bimaculata. The presence of 67 to 70 scales along the lateral line from the supracleithrum to the hypural joint separates S. binotata from all those taxa that have 62 or fewer scales in that series.

DESCRIPTION.—Body elongate, somewhat compressed, more so in smaller specimens. Dorsal profile of head straight or very slightly convex. Dorsal profile of body straight or very slightly convex from rear of head to origin of dorsal fin; straight or slightly convex, posteroventrally slanted at base of dorsal fin, slightly concave to slightly convex from base of last dorsal-fin ray to caudal peduncle. Dorsal surface of body with distinct median keel anterior to dorsal fin, keel most pronounced posteriorly; body smoothly rounded transversely posterior to fin. Ventral profile of body straight from tip of lower jaw to vertical through origin of pectoral fin, gently convex from that point to origin of anal fin, then sigmoid to caudal peduncle. Prepelvic region broadly but obtusely flattened, with obtuse lateral keels. Postpelvic region rounded. Anus distinctly anterior of origin of first anal fin-ray, with 9 to 11 scales in intervening space.

Greatest depth of body 0.25–0.31 [0.31]; snout tip to origin of dorsal fin 0.44–0.48 [0.45]; snout tip to origin of anal fin 0.82–0.85 [0.84]; snout tip to origin of pelvic fin 0.47–0.50 [0.48]; snout tip to anus 0.70–0.73 [0.71]; origin of dorsal fin to hypural joint 0.57–0.61 [0.60]. Dorsal-fin profile acute, less so with increasing age; anteriormost rays approximately three times length of ultimate ray. Pectoral-fin profile acute; length of pectoral fin 0.16–0.25 [0.17], extends about three-quarters distance to vertical line through origin of pelvic fin in smaller specimens, slightly over one-half distance in larger individuals. Pelvic-fin profile acute, length of pelvic fin 0.20–0.24 [0.23], reaches one-half to two-thirds distance to origin of anal fin. Caudal fin forked. Adipose dorsal fin well developed. Border of anal fin emarginate, anteriormost branched rays about three times length of ultimate ray. Caudal peduncle depth 0.10–0.11 [0.11].

Head distinctly pointed in profile, head length 0.23–0.26 [0.23]; upper jaw longer, mouth inferior, anterior portion of buccopharyngeal complex consisting of three weakly developed fleshy folds without fleshy lobulate bodies; snout length 0.28–0.32 [0.30]; nostrils very close, anterior circular, posterior crescent-shaped, with aperture closed by thin flap of skin separating nares; orbital diameter 0.28–0.32 [0.29]; adipose eyelid present, with broad, vertically ovoid opening over center of eye; length of postorbital portion of head 0.39–0.45 [0.42]; gape width 0.27–0.33 [0.33]; interorbital width 0.41–0.43 [0.43].

Pored lateral-line scales to hypural joint 67 to 72 [67]; all scales of lateral line pored, canals in scales straight; S to 7 series of scales extend beyond hypural joint onto caudal-fin base; 11½ to 13 [12½] scales in transverse series from origin of rayed dorsal fin to lateral line; 8½ to 10 [8½] scales in transverse series from lateral line to origin of anal fin.

Rayed dorsal-fin rays ii,9 or iii,9 (when three unbranched rays present, first very short) [iii,9]; anal-fin rays ii,7 or iii,7 (when three unbranched rays present, first very short) [iii,7]; pectoral-fin rays 15 to 17 [16]; pelvic-fin rays i,9 [i,9].

Total vertebrae 36 (1), 37 (14), 38 (1).

COLOR IN ALCOHOL.—Holotype retains guanine on scales; overall coloration silvery, darker on dorsal portions of head and body. Other specimens fixed in formalin, with reduced guanine on scales; overall coloration tan to light brown, darker on dorsal portions of head and body. Distinct, narrow, deep-lying, dark band of pigmentation along midlateral surface of body from supracleithrum to caudal peduncle; band expands into broad field of slightly dusky pigmentation on peduncle. Midlateral stripe and dark pigmentation on peduncle masked by guanine on scales in some specimens. Distinct, very dark spot along dorsal midline immediately anterior of dorsal fin; spot approximately circular, somewhat more transversely elongate in smaller individuals. Anteroposteriorly elongate spot of dark pigmentation along dorsal midline immediately posterior of tip of supraoccipital spine; somewhat less apparent in larger individuals. Mid-dorsal line from rear of dorsal fin to caudal peduncle very dark. Few variably sized, dark spots approximately size of pupil scattered on lateral and dorsolateral portions of body (Figure 15). Rays of caudal fin outlined by series of small chromatophores; lower lobe of caudal fin dusky. Other fins hyaline.

DISTRIBUTION.—Upper Río Madeira system in Bolivia and Peru (Figure 14).

COMPARISONS.—The distribution of Steindachnerina binotata is known to overlap that of three congeners, S. bimaculata, S. dobula. and S. guentheri. The overall body form, high lateral-line scale and vertebral counts, and various details of the pigmentation pattern in S. binotata readily discriminate that species from each of the cited taxa.

MATERIAL EXAMINED.—31 specimens (17, 89.6–133.0).

BOLIVIA. Beni: Rurrenbaque, CAS-IU 17285, 1 (133.0, holotype of Curimatus binotatus). La Paz: San Miguel de Huachi (Río Boopi), USNM 279335, 1 (131.7).

PERU. Madre de Dios: Río Tambopata, Puerto Maldonado, USNM 301960, 1 (89.6; cleared and counterstained for cartilage and bone). Parque Nacional Manú, streams flowing into Río Manú, vicinity of Pakitza, USNM 295339, 28 (14, 92.5–123.5).