Moenkhausia hysterosticta, Lucinda, Paulo H. F., Malabarba, Luiz R. & Benine, Ricardo C., 2007

Lucinda, Paulo H. F., Malabarba, Luiz R. & Benine, Ricardo C., 2007, On a new species of the genus Moenkhausia Eigenmann (Ostariophysi: Characidae), Zootaxa 1525, pp. 61-68 : 62-65

Moenkhausia hysterosticta , new species

Figs. 1–3 , Tables 1 and 2

Holotype. ( Fig. 1 ). MCP 32559, 43.1 mm SL, Rio Tocantins, Ipueiras, approximately 11o19’S 48o28’W, Tocantins, Brazil, 24 Oct 1999, Núcleo de Estudos Ambientais - Universidade Federal do Tocantins ( NEAMB).

Paratypes. Brazil. Tocantins. MCP 32560, 2 (40.5–45.3 mm SL), and UNT 4475, 2 (42.3–43.4 mm SL), collected with the holotype. MCP 32561, 19 (4 c&s) (39.2–45.0 mm SL), and UNT 4476, 12, (39.4–45.4 mm SL), Lageado, Funil, Rio Tocantins, 0 9o 45’02”S 48o21’56”W, 17 Oct 1999, NEAMB. UNT 3887, 15 (34.7– 41.5 mm SL), Rio Tocantins, Ipueiras, approximately 11º19’S 48º28’W, 26 Jul 2004, NEAMB. UNT 4474, 7 (36.8–40.2 mm SL), Rio Tocantins, Porto Nacional, 10o43’15”S 48o25’14”W, 18 Nov 1999, NEAMB.

Non-type specimens: Venezuela. Apure. MCNG 45346, 12, (36.8–43.5 mm SL), Río Apure, Modulo Fernando Corrales UNELLEZ, dique Noreste 0 7o 34’40”N 69o32’40”W, 3 Feb 1981, D. Taphorn, C. Lilyestron, and S. Reid.

Diagnosis. Moenkhausia hysterosticta is distinguished from congeners by the presence of a dark spot in the upper caudal-fin lobe and by the large and irregularly shaped humeral spot located above the fifth to ninth perforated scale of the lateral line.

Description. Morphometric data in Table 1. Body short and compressed. Predorsal and preventral profiles nearly equally convex. Greatest depth at dorsal-fin origin. Body profile along anal-fin base nearly straight to slightly convex. Caudal peduncle short, nearly square. Dorsal and ventral profiles of caudal peduncle concave. Head small. Eyes large, corresponding to almost half head length. Maxilla positioned at angle of approximately 45 degrees relative to long body axis. Maxilla short; posterior tip extending beyond vertical line crossing at anterior border of eyes.

Two series of premaxillary teeth. Teeth of outer series tricuspid, smaller than inner series, numbering 3 to 5. Five teeth, pentacuspid, in inner series. One or two maxillary teeth; anterior teeth tricuspidate, and second tooth, when present, smaller and conical. Four or five anterior large, pentacuspid, dentary teeth posteriorly followed by slightly smaller and usually tricuspid teeth, and 4 to 10 much smaller ones, conical ( Fig.2 ).

Dorsal-fin rays ii, 9 (n = 58). First unbranched ray about one-half length of second. Dorsal-fin origin at midlength of body. Entire adipose-fin base located above posterior portion of anal-fin base. Anal-fin rays iv, 24–27 (x = 25.6, n = 57). Anal-fin origin at or slightly posterior to vertical line through insertion of last dorsal-fin ray. Anteriormost portion of anal fin concave; last unbranched and anterior 4 branched rays gradually decreasing in size; remaining portion of anal-fin rays shorter and with equal lengths giving smooth profile to remaining fin. No hooks observed. Pectoral-fin rays i, 10–13 (x = 11.1, n = 57), reaching to or near pelvic-fin origin. Pelvic-fin rays i, 7 (n = 56). Pelvic-fin origin anterior to vertical through dorsal-fin origin; longest ray falls short of anal-fin origin. Lower lobe of caudal fin slightly longer than upper lobe. Scales cycloid. Lateral line complete; 29–35 scales (x = 31.2, n = 36). Scale rows between dorsal-fin origin and lateral line 5 (n = 58). Scale rows between lateral line and pelvic-fin origin 4 (5 in one specimen; n = 58). Predorsal scales 8 or 9 (x = 8.8, n = 58), arranged in regular series. Scale sheath on anal-fin base consisting of one row of small scales, covering approximately anterior half of anal-fin base. Small and deciduous scales covering approximately half length of dorsal caudal-fin lobe and third proximal length of ventral caudal-fin lobe. Precaudal vertebrae 13 or 14 (x = 13.3); caudal vertebrae 19 or 20 (x = 19.3); total vertebrae 32–34 (x = 32.6) (counts taken in four c&s specimens).

Type-series Non-types

(Tocantins basin) (Orinoco basin)

Characters H n range mean n Range mean Standard Length (mm) 43.1 54 35.7–45.4 40.6 12 36.8–43.5 40.7

Percents of Standard Length

Body depth 38.5 54 33.8–42.7 38.0 12 38.4–42.6 40.4 Head length 28.1 54 26.9–29.5 28.0 12 26.3–28.3 27.2 Predorsal distance 49.7 54 48.3–53.1 50.6 12 47.7–51.8 50.3 Prepelvic distance 50.6 54 47.3–53.4 50.1 12 46.7–50.4 48.3 Preanal distance 63.8 54 61.9–69.1 66.2 12 62.9–66.4 64.7 Dorsal-fin base 14.2 54 11.3–16.1 13.9 12 13.3–15.5 14.6 Anal-fin base 32.7 54 27.0–34.9 30.9 12 30.3–34.9 32.2 Caudal peduncle length 10.7 54 7.1–11.3 8.8 12 7.8–10.7 8.8 Caudal peduncle depth 10.0 54 9.6–12.0 11.0 12 9.6–11.4 10.5 Dorsal-fin length 29.5 54 27.6–31.9 29.7 12 29.4–33.5 31.9 Pectoral-fin length 20.4 54 19.5–23.2 21.7 12 21.4–23.5 22.2 Pelvic-fin length 14.6 54 14.6–17.8 16.6 12 16.7–18.0 17.3

Percents of Head Length

Upper jaw length 38.8 54 33.9–45.5 38.5 12 36.7-41.8 40.5 Snout length 22.3 54 20.0–26.0 23.7 12 22.3-27.8 24.2 Orbital diameter 45.5 54 42.2–50.5 47.3 12 44.7–50.3 48.1 Interorbital width 35.5 54 34.4–38.8 36.0 12 33.0–37.1 35.0 Color in alcohol. Eye black with greenish brown pupil. Ground color pale brown, darker in upper half. Border of scales and underlying skin of dorsal half of trunk replete with light brown chromatophores, conferring a very light reticulate pattern to this region. Inner surface of opercle and associated bones covered with dark chromatophores; patch formed by these chromatophores visible externally through opercle and preopercle. Weak, dark brown oblique line of chromatophores on body side above anal-fin base. Dorsal fin weakly pigmented; more pigmented specimens with series of brown chromatophores along both sides of each dorsalfin ray. Pectoral, pelvic and anal fins hyaline. A dark spot in the half proximal length of the upper caudal-fin lobe; remaining portions of the upper and all lower caudal-fin lobe scattered pigmented with dark chromatophores, not forming conspicuous spot. Humeral spot highly variable in size and shape; in less pigmented specimens located nearly over sixth scale of second scale row above lateral line; in more pigmented specimens covering fifth to eighth lateral line scales and extending two rows above and one row below lateral line. Wide dark midlateral band along flank from vertical passing through dorsal-fin origin to base of caudal-fin rays.

Sexual dimorphism. No apparent sexual dimorphism was observed.

Etymology. From the Greek hysteros -, after or posterior, and stictus, spot; refers to the humeral spot, which is located posteriorly on body side.

Distribution. Moenkhausia hysterosticta is currently known from middle portions of the Rio Tocantins in Porto Nacional, Ipueiras, and Lageado ( Fig. 3 ).

Comments. Moenkhausia hysterosticta occurs in Rio Tocantins, but morphologically similar specimens were found far to the west in the Río Apure, Río Orinoco drainage, Venezuela. The population from the Río Apure differs from the Rio Tocantins population mainly in the number of branched anal-fin rays (26–29, mean = 27.5 versus 24–27, mean = 25.6) and dentary teeth (13–17, mean = 14 versus 9–15, mean = 12.7), but present much overlapping in the remaining morphometric and meristic traits ( Tables 1 and 2 ). In the lack of comparative material from intermediate regions between the two river basins, we prefer to identify the population from the Río Apure tentatively as M. hysterosticta .

Figures

FIGURE 1. Moenkhausia hysterosticta, holotype, 43.1 mm SL, MCP 32559, Brazil, Tocantins, Rio Tocantins, Ipueiras.

FIGURE 2. Moenkhausia hysterosticta, MCP 32561, paratype, 41.1 mm SL. Scanning electronic micrograph of left side upper and lower jaws teeth.

FIGURE 3. Distribution of Moenkhausia hysterosticta. Some symbols represent more than one lot or locality. T = Typelocality.