Moenkhausia britskii, Azevedo-Santos, Valter M. & Benine, Ricardo C., 2016

Azevedo-Santos, Valter M. & Benine, Ricardo C., 2016, A new species of Moenkhausia (Characiformes, Characidae) from the Ica River, Amazon Basin, northern Brazil, Zoosystematics and Evolution 92 (2), pp. 203-209 : 203-205

Taxon classification Animalia Characiformes Characidae

Moenkhausia britskii sp. n. Fig. 1

Holotype.

MZUSP 120691, 52.9 mm SL, Brazil, Amazonas State, Santo Antônio do Içá Municipality, Rio Içá, approximately 60 km above its mouth, 3°0 ’7.68” S, 69°2 ’49.52” W, collected by H. A. Britski, N. A. Menezes, J. C. Garavello, T. R. Roberts, S. Gerken, 18 Oct 1968.

Paratypes.

MZUSP 17537, 16 (1 c&s), 41.3-58.3 mm SL, same data as the holotype.

Diagnosis.

Moenkhausia britskii sp. n. differs from all congeners, except Moenkhausia grandisquamis ( Müller & Troschel, 1845), Moenkhausia tergimacula Lucena & Lucena, 1999 and Moenkhausia xinguensis (Steindachner, 1882), by the presence of a single humeral spot, presence of a silvery lateral stripe, absence of a dark line at the base of the anal-fin rays, absence of a caudal lobule mark, dorsal fin hyaline, five series of scales above lateral line and four series of scales below lateral line. Moenkhausia britskii differs from Moenkhausia tergimacula by the absence of a dark spot located anteriorly to the dorsal-fin origin; and from Moenkhausia xinguensis by the scales showing upward and downward bent radii (vs. scales with straight radii) (Fig. 2). Finally, it differs from Moenkhausia grandisquamis by having a larger humeral spot, located over the third to fifth or fourth to sixth lateral-line scales and extending vertically over three or four horizontal scale rows above the lateral line (vs. smaller humeral spot, located over second to third or third to fourth scale of the series immediately above the lateral line) (Fig. 3). The new species also differs by having four or five cusps on the second tooth of the inner row of the premaxilla (Fig. 4) (vs. eight, seven, occasionally six cusps on the second tooth of the inner row of the premaxilla in Moenkhausia grandisquamis ).

Description.

Morphometric data are given in Table 1. Greatest body depth at dorsal-fin origin. Dorsal profile of body slightly convex from tip of supraoccipital spine to dorsal-fin origin. Dorsal-fin base posteroventrally inclined. Profile straight or slightly convex from end of dorsal fin to adipose-fin origin; adipose-fin base posteroventrally inclined; caudal peduncle concave both dorsally and ventrally; ventral profile of body convex from tip of lower jaw to anal-fin origin; anal-fin base posterodorsally inclined. Prepelvic region transversally flattened, mainly at pelvic-fin insertion.

Mouth terminal. Posterior tip of maxilla extending beyond vertical through anterior margin of orbit. Premaxillary teeth arranged in two rows; outer row with 4(1), 5*(15) or 6 (1) tricuspidate teeth with central cusp longer; inner row with 5* (17) tetra-to pentacuspidate teeth (Fig. 5). Maxilla with 1* (14) or 2(3) tricuspid teeth. Dentary with 4* (17) tetra- to pentacuspidate teeth; central cusp usually longer, followed by five to ten small teeth decreasing in size posteriorly, with one to three cusps.

Dorsal-fin rays ii, 9. Pectoral-fin rays i, 10 (1), i, 11 (10), or i, 12* (6). Pelvic-fin rays i, 7. Anal-fin rays iii, 23 (4), iii, 24 (4), iii, 25* (8), or iii, 26 (1). Adipose fin present.

Scales cycloid with striae curved upward and downward. Lateral line slightly curved, with 30 (3), 31 (6), 32* (6) or 33(2) pored scales. Five transversal scales above lateral line and four transversal scales below lateral line. A single series of scales covering base of second to eleventh branched anal-fin rays. Small scales covering the proximal two-third of caudal-fin lobes.

Total number of vertebrae 32 (2). Gill rakers on lower limb 8 (1); 11* (15); 12 (1); gill rakers on upper limb 7(1), 8(9) or 9*(7). Supraneurals 4 (2).

Color in alcohol.

Overall coloration yellow tan. Concentration of few dark chromatophores on upper lip. Infraorbital and opercular series light silvery due to the scarce remaining guanine pigmentation. Dark chromatophores more densely concentrated along dorsal midline. Sparsely distributed dark chromatophores dorsal of horizontal septum. A dark line marks the horizontal septum. A silvery-gray midlateral stripe extending from posterior margin of humeral spot to caudal peduncle. Irregularly shaped, humeral spot located over third to fifth or fourth to sixth lateral-line scales and extending vertically over three or four horizontal scale rows above lateral line. Paired fins and anal fin hyaline. Adipose with very few dark chromatophores.

Distribution.

Known from the Igarapé da Cachoeira, Içá River, Amazon basin, Santo Antônio do Içá, Amazonas, Brazil (Fig. 6).

Etymology.

The specific epithet britskii is in honor of Dr. Heraldo Antônio Britski, collector of this new species and for his enormous and valuable contributions to our knowledge of the Neotropical Ichthyology.