Shining Pencilfish

Nannostomus nitidus

HOLOTYPE.—MZUSP 12920, male, SL 34.7 mm; Brazil, State of Pará, Igarapé Candiru-Mirim near Badajós, Rio Capim, 29 Aug 1970, Naércio Menezes, E.P.A.

PARATYPES.—18, MZUSP 12921–12938, SL 16.3 to 33.3 mm; same data as holotype. 8, USNM 216204, SL 17.0 to 34.5 mm; same data as holotype. 5, ANSP 137388, SL 18.3 to 34.1 mm; same data as holotype. BMNH 1976–11–8–1–5, SL 18.5 to 35.2 mm; same data as holotype.

DIAGNOSIS.—Primary and secondary horizontal stripes present, all others absent. Nocturnal oblique bands present, narrow, anterior band not extending posteriorly much beyond a line extending vertically through anterior dorsal-fin origin; permanent blotches absent. Adipose fin present. Scales in lateral series 23 to 25, usually 24. Perforated lateral-line scales 0 to 2. Total vertebrae 34 or 35. Gill rakers 10 to 11 + 16 to 18. Simple conic teeth in inner dentary row 2 or 3, laterally placed. Principal caudal-fin rays 10/9, 10 terminating posteriorly in dorsal lobe, 9 in ventral lobe. Eye about 100 to 110% of least bony interorbital width. Body depth about 23 to 25% of standard length, and least depth of caudal peduncle about 9% of standard length. Anal fin of male moderately modified, having slightly thicker rays than that of female.

DESCRIPTION.—Body elongate, compressed in region of caudal peduncle, greatest body depth at origin of dorsal fin [239] 235–253, x = 243; least depth of caudal peduncle [089] 088–094, x = 090; snout tip to origin of dorsal fin [513] 507–536, x = 519; snout tip to origin of anal fin [764] 734–782, x = 760.

Head conic, snout obtuse. Head [242] 238–265, x = 251; eye [079] 079–088, x = 084; least width of bony interorbital [078] 075–079, x = 077.

Premaxillary with 6 teeth, first (anterior) 5 or 6 with 6 subequal cusps, and sixth tooth sometimes small but with 6 cusps, median cusp largest. Maxillary toothless. Dentary with 6 teeth in outer row, each bearing 6 subequal cusps. Inner dentary row with 2 or 3 conic teeth, placed laterally in jaw (two alizarin preparations).

Gill rakers [11 + 18], 10 + 16 in one and 10 + 17 in a second alizarin preparation.

Dorsal fin ii, 8; anal fin iii, 8; pectoral fin i, 11; pelvic fin ii, 7; and principal caudal-fin rays 10/9 posteriorly terminating in dorsal lobe and 9 in ventral lobe in all specimens. Adipose fin present in all specimens.

Scales belonging to third horizontal series and lying ventral to dorsal fin having anterior field with 3 radial grooves and posterior field with 2 radial grooves. Dorsal and ventral fields each with 1 radial groove. Scales in a lateral series [25] 23 to 25, x = 24.2. Lateral-line scales [0] 0 to 2, usually on third and fourth scale horizontal scale row; 10 predorsal scales in all specimens.

Total vertebrae [35] 9 paratypes with 34 and 11 with 35.

COLOR IN ALCOHOL.—Dorsal surface of head dark brown, more or less evenly covered with small, dark brown chromatophores. Back dorsal to secondary horizontal stripe dark brown but not as dark as top of head, rather densely covered with moderate-sized brown chromatophores except for distal free margins of scales, where chromatophores less dense than central portions of scales. Each scale bordered by a pale brown band. No dark brown longitudinal stripes occur dorsal to secondary stripe. Primary horizontal stripe very dark brown, nearly black, consisting of a dense aggregation of large, very dark brown chromatophores. Primary stripe originating anteriorly at tips of upper and lower jaws, extending across orbital bones to reach anterior border of eye, continuing across eye, postorbital and preopercular areas and operculum to include a few dark brown chromatophores scattered on fleshy opercular flap. On body, primary stripe extending from under fleshy opercular flap, beginning at cleithrum and supracleithrum, and continuing posteriorly over ventral half of third horizontal scale row and dorsal half of fourth horizontal scale row, ending on scales covering base of ventral caudal-fin lobe. Primary stripe apparently not extending onto fin rays of ventral caudal-fin lobe. Secondary dark horizontal stripe extending from just dorsal to opercular bone (where it joins head dorsally) to across middle of second horizontal scale row. Secondary horizontal stripe fading to color of back just posterior to a vertical line extending ventrally from posterior base of dorsal fin. Secondary stripe in preserved specimens consisting of a cluster of very dark brown chromatophores concentrated at center of each scale of second horizontal scale row, forming a series of spots. Pale yellow to white stripe, situated between primary and secondary stripes, occupying dorsal half of third scale row and ventral half of second scale row, and containing a few brown chromatophores scattered along scale margins. Pale stripe also contains dorsal portions of anterior and posterior oblique bands. Anterior oblique band in area of pale stripe extending ventroanteriorly from mostly seventh, eighth, and ninth scales of third horizontal scale series ventral to primary stripe, where it covers all of ventral portions of fifth and sixth scales (counting dorsal postcleithrum as a scale) of fourth longitudinal scale row. Posterior oblique band covering about 17th and 18th scales of third horizontal scale row, and extending ventrally to cover parts of 15th through 18th scales of fourth longitudinal scale row, which extends just ventral to primary horizontal stripe. Sides ventral to primary horizontal stripe nearly devoid of pigment. No evidence of a tertiary horizontal stripe and only a very few scattered, small, dark brown chromatophores around vent in either sex. All rayed fins except caudal fin with small brown chromatophores along edges of bony rays producing hyaline but slightly dusky fins. Pectoral, and especially pelvic and anal, fins with more distal portions of ray, especially ray tip, with dark brown chromatophores, forming faintly darkened edges to fins. Caudal fin nearly hyaline except for narrow black edge above dorsal and ventral borders.

Life colors unknown.

ETYMOLOGY.—The name nitidus is a Latin adjective for “neat, elegant, or shining.”

RELATIONSHIPS.—Although Nannostomus nitidus keys to Nannostomus digrammus in the artificial key of Weitzman and Cobb (1975), no relationship between N. nitidus and N. digrammus is hypothesized, especially since at large sizes (to 34 and nearly 35 mm SL), males of N. nitidus lack the highly specialized fin rays and increased length of the anal fin found in males of N. digrammus over 24 to 25 mm in standard length. Nannostomus nitidus further differs from N. digrammus in having 10 to 11 + 16 to 18 (rather than 7 + 14) gill rakers. The two species differ in the details of color pattern; for example, N. digrammus has the primary horizontal stripe continued as a wedge onto the caudal fin, whereas the wedge is absent on this fin in N. nitidus. I found nothing in the color pattern or morphometric and meristic characters that suggests any hypothesis of sister group relationship on the part of nitidus with any other species of Nannostomus.