Moenkhausia eurystaenia, Marinho, 2010

Marinho, Manoela M. F., 2010, A new species of Moenkhausia Eigenmann (Characiformes: Characidae) from the rio Xingu basin, Brazil, Neotropical Ichthyology 8 (3), pp. 655-659 : 656-658

Moenkhausia eurystaenia , new species

Figs. 1-2

Holotype. MZUSP 106058 , 36.8 mm SL, rio Von Den Stein , on the road to Água Limpa , 13°14’19”S 54°53’01”W, rio Ronuro drainage , rio Xingu basin , Nova Ubiratã, Mato Grosso, Brazil, 24 Oct 2004, J. L. Birindelli, O. T. Oyakawa, C. R. Moreira, M. I. Landim, A. K. Oliveira, A. Datovo & J. C. Nolasco.

Paratypes. CPUFMT 610 , 3, 25.2-28.6 mm SL; DZSJRP 12547 , 3, 24.4-24.6 mm SL; INPA 34095 , 3, 23.3-26.1 mm SL, MCP 45547 , 3, 24.9-26.1 mm SL, MPEG 18924 , 3, 25.5-27.2 mm SL, MZUSP 91404 , 109, 18.5-36.8 mm SL (17, 25.6-36.8 mm SL), 3 c&s, 23.3-26.1 mm SL, USNM 398648 , 3, 23.2-27.5 mm SL, all with same data of holotype .

Diagnosis. Moenkhausia eurystaenia is distinguished from all congeners, except M. heikoi and M. phaeonota , by the presence of a dark, broad stripe, from the opercle to the end of the caudal peduncle ( vs. stripe, when present, narrow and frequently originating approximately at vertical through dorsal-fin origin). The new species is distinguished from M. heikoi by having 18-21 branched anal-fin rays ( vs. 24-26), by the absence of a round blotch at the end of the caudal peduncle ( vs. blotch present), and by the dark stripe formed by relatively small chromatophores ( vs. large chromatophores). Moenkhausia eurystaenia is distinguished from M. phaeonota ( Fig. 3 ) by its more dispersed dark stripe, not well delimited ( vs. less disperse, relatively well delimited), the anterior portion of the stripe darker at horizontal septum ( vs. darker below horizontal septum), the deep dark pigmentation along horizontal septum extending anteriorly up to umeral region ( vs. extending up to vertical through pelvic-fin origin), the melanophores of interradial membranae between first and fifth branched dorsal-fin rays restricted to the edge of lepidotrichia ( vs. spread over interradial membranae), the distance between snout to pelvic-fin origin 46.9-50% SL, n = 35 ( vs. 43.2-46.6, n = 30), the distance from snout to analfin origin 62.1-65.4% SL, n = 35 ( vs. 55.9-61.2, n = 30), the analfin base length 25.1-28.4% SL, n = 35 ( vs. 28.5-33.8, n = 30), and the number of vertebrae 34, n = 13 ( vs. 36-37, n = 12).

Description. Morphometrics in Table 1 . Largest specimen examined 36.8 mm SL. Body compressed, greatest body depth slightly ahead of vertical through dorsal-fin origin. Dorsal profile of body convex from upper lip to vertical through anterior edge of nostril; straight from latter point to tip of supraoccipital spine; convex from supraoccipital spine to dorsal-fin origin; straight to slightly convex and posteroventrally inclined along dorsal-fin base; straight to slightly convex from posterior terminus of dorsal-fin base to adipose-fin origin; slightly concave along caudal peduncle. Ventral profile of body convex from tip of lower jaw to pelvicfin origin; straight from pelvic-fin origin to anal-fin origin; straight and posterodorsally inclined along anal-fin base and slightly concave along caudal peduncle.

Jaws vertically aligned, mouth terminal. Premaxillary teeth in two rows, outer with 3*(13) or 4(22) tricuspid teeth, inner with five tri- to pentacuspid teeth. Maxilla reaching vertical through anterior fourth of orbit, with 2(14), 3*(17), or 4(1) unito tricuspid teeth. Dentary with three pentacuspid teeth, followed by smaller tricuspid and series of 5-10 small conical teeth decreasing gradually in size ( Fig. 2 ).

Pectoral-fin rays i,10*(30), 11(4), or 12(1), reaching pelvicfin origin in adults, not reaching in juveniles, when adpressed. Pelvic-fin rays i,7, reaching pelvic-fin origin in adults, not reaching in juveniles, when adpressed. Anal-fin rays iv(2) or v(1), and 18(6), 19(13), 20*(13), or 21(3); last unbranched and first four or five branched anal-fin rays longer then remaining rays. Supraneurals 4, all rod-shaped, with bony lamellae in upper portion. Dorsal-fin rays ii,9, first unbranched dorsal-fin ray almost half length of second unbranched ray. Dorsal-fin origin slightly ahead midbody, located at vertical through anterior third of pelvic fin; base of last dorsal-fin ray at vertical through anal-fin origin. First dorsal-fin pterygiophore behind neural spine of 9 th vertebra. Adipose-fin origin situated approximately at vertical through 14 th to 16 th branched analfin rays. Caudal-fin rays i,17,i*(32) or i,16,i(2). Caudal fin forked, with lobes of similar size. Dorsal procurrent caudal-fin rays 11, ventral procurrent caudal-fin rays 10(1) or 11(2).

Lateral line completely pored, slightly curved ventrally, with 32(3), 33(9), 34*(8), or 35(4), perforated scales. Longitudinal scale rows between dorsal-fin origin and lateral line 5; longitudinal scale rows between lateral line and pelvicfin origin 3. Single row of 9*(15), 10(19) or 11(1) predorsal scales. Single row of 3-5 scales overlying base of anteriormost anal-fin rays. Scale rows around caudal peduncle 14. Small scales along first third of upper caudal-fin lobe and first half of lower lobe.

Vertebrae 34(13). Branchiostegal rays 4. First gill arch with 17(2) or 19(1) gill rakers: six on epibranchial, one on intermediate cartilage, eight(2) or 10(1) on ceratobranchial, and two on hypobranchial. Gill rakers without small denticles.

Color in alcohol. Overall ground color yellowish. Infraorbital, opercular and gular areas silvery. Dorsal portion of head and body dark. Dark chromatophores scattered at infraorbital and opercular areas, upper and lower jaws. First three dorsal horizontal scale rows on body with slightly reticulated pattern, formed by scales bordered by dark pigment. Faint pale stripe posterodorsally from eye to caudal peduncle. A broad stripe on body, from opercle to end of caudal-peduncle, darker over horizontal septum, fading ventrally, and extending over middle caudal-fin rays as faint stripe. Smaller specimens with clearer stripe. Narrow midlateral dark stripe at horizontal septum conspicuous, formed by deeper dark chromatophores, extending from humeral region to end of caudal peduncle. Concentration of dark chromatophores immediately posterior to opercle, on first to fourth lateral scales, forming inconspicuous triangular humeral blotch. Scattered dark chromatophores above anal-fin base. All fins with dark chromatophores along edge of lepidotrichia.

Distribution. Moenkhausia eurystaenia is known from the type-locality in the rio Ronuro drainage, upper rio Xingu basin, Brazil ( Figs. 4-5 ).

Etymology. The specific name eurystaenia comes from the Greek eurys, broad, and the Latin taenia, band, a reference to the broad dark stripe.

Figures

Fig. 1. Moenkhausia eurystaenia, holotype, MZUSP 106058, 36.8 mm SL, rio Von Den Stein, rio Xingu basin, Nova Ubiratã, Mato Grosso, Brazil.

Fig. 2. Scanning electron microscope photograph of left side of upper and lower jaw of Moenkhausia eurystaenia, MZUSP 91404, paratype, 24.3 mm SL. Scale bar = 0.5 mm.

Fig. 3. Moenkhausia phaeonota, MZUSP 91403, 26.3 mm SL, collected in sympatry with M. eurystaenia at rio Von Den Stein, rio Xingu basin, Nova Ubiratã, Mato Grosso, Brazil.

Fig. 4. Type-locality of Moenkhausia eurystaenia in the upper rio Xingu basin, Brazil.

Fig. 5. Rio Von Den Stein in the upper rio Xingu basin, Brazil, type-locality of Moenkhausia eurystaenia.