Moenkhausia justae Eigenmann 1908

Moenkhausia justae Eigenmann, 1908

(Figs. 8 a–b, 9b, Table 2)

Moenkhausia justae Eigenmann 1908: 102. Type locality: “Uncertain in Amazon, Brazil ”.

Diagnosis. Moenkhausia justae is distinguished from M. jamesi, M. ischyognatha, M. alesis and M. sthenosthoma by the number of teeth in the maxilla (one tooth with five cusps vs an edentulous maxilla in the last four) and by the number of cusps on the fourth dentary tooth (six vs three to five in the last four) (Fig. 9 b). Moenkhausia justae is further distinguished from M. ischyognatha and M. sthenosthoma by the number of scale rows between lateral line and dorsal-fin origin (eight vs seven in the last two). Additionally, it differs from M. ischyognatha by its greater head depth (34.9–40.2% in SL vs 29.3–32.6 in SL in the last three). It also differs from M. jamesi by the number of scale rows between lateral line and the midventral scale series (seven to eight vs six scale rows in M. jamesi).

Description. Morphometric data summarized in Table 2. Largest specimen examined 56.9 mm SL. Body compressed and deep. Greatest body depth slightly anterior to or at dorsal-fin origin. Dorsal profile of head slightly convex; straight to slightly concave along the occipital spine; slightly convex to convex from tip of supraoccipital spine to end of dorsal-fin base; straight to slightly convex from end of dorsal fin up to end of adipose fin; caudal peduncle concave in dorsal and ventral margins; ventral profile slightly convex from tip of snout to end of anal fin.

Mouth terminal. Maxilla only reaching the vertical through anterior margin, and not trespassing anterior third of second infraorbital. Premaxillary teeth in two rows. Inner row with five tetracuspidate (symphyseal) or pentacuspidate teeth with median cusp pronounced, the first two or three teeth from the symphysis with cusps arranged in a pronounced arch when examined from a ventral view; outer row with four to five pentacuspidate teeth; one pentacuspidate tooth on maxilla. Dentary bearing four*(52) or five (15) penta to heptacuspidate teeth with central cusp longest followed by two to four distinctly small conical or tricuspidate teeth. Fourth dentary tooth with six to seven cusps. First two or three dentary teeth from the symphysis with cusps arranged in a pronounced arch when examined from a dorsal view.

Moenkhausia jamesi (n=73) Moenkhausia justae (n=75) Dorsal-fin rays ii,9. Pectoral-fin rays i,11(3), 12*(46), 13(18). Tip of pectoral fin extends slightly beyond anterior insertion of pelvic fin. Pelvic-fin rays i,7, tip of adpressed pelvic fin not reaching anal fin. Anal-fin rays iv,28*(12), 29(25), 30(21), 31(9). Caudal fin forked with i,9,8,i.

Scales cycloid. Lateral line with 35(2), 36*(12), 37(35), 38(17) perforated scales; Scale rows between lateral line and dorsal-fin origin 7(21) 8*(45). Scale rows between lateral line and midventral scale series 7(60), 8*(7). Circumpeduncular scale rows 13(2), 14*(8), 15(21), 16(25), 17(6), 18(3). Scale sheath along anal-fin base 7–21, in one series, covering base of anteriormost rays. Small scales covering proximal two-third of caudal-fin lobes.

First gill arch with 11(6), 12(40), 13(10) gill rakers on lower limb and 8(20), 9(34), 10(6) on upper limb. Total vertebrae 32. Supraneurals 4.

Color in alcohol. Overall coloration slightly silvery or yellow tan. Field of few dark chromatophores on upper lip and maxilla. Infraorbital and opercular series silvery due to the presence of guanine pigmentation. Dark chromatophores more densely concentrated along entire dorsal midline. Sparsely spread dark chromatophores dorsal of horizontal skeletogenous septum. Dark line over horizontal skeletogenous septum. Conspicuous silver midlateral stripe extending from posterior margin of opercle to base of median caudal fin-rays. In some individuals, silver stripe is not preserved. Irregularly shaped humeral mark located over fourth to eight lateral-line scales and extending vertically over four-five horizontal scale rows above and over one-two horizontal scale rows below lateral line. Paired fins and anal fin hyaline. Round dark spot at the base of the caudal-fin rays formed by few chromatophores. Adipose with very few dark chromatophores (Figs. 8 a–b).

Distribution. Moenkhausia justae occurs along Rio Amazonas basin and the middle and lower Rio Araguaia, and appears to be restricted in Amazon lowlands area, as defined by Lima & Ribeiro (2011) (Fig. 4).

Remarks. Lima et al. (2003) briefly discussed that the proposition of Eschmeyer et al. (1998) indicating that the type locality of M. justae could be Rio Paraiba do Norte, João Pessoa, Paraíba was undisclosed and that recent collections at João Pessoa and other sites in northeastern Brazil did not reveal specimens that could be assigned to this species. Although the type locality of M. justae was not provided at the original description (Eigenmann 1908), this author, in 1917, stated that the single (type) specimen of M. justae “came with others from Dr. Justa through Major Coutinho and was probably found in the neighborhood of Manaos”. In fact, an image of the catalogue book of the Museum of Comparative Zoology (available at: http://ids.lib.harvard.edu/ids/view/36195367?buttons=y) indicates that the locality of M. justae is “Prob. Manaos” (= probably Manaus). According to Lima et al. (2003), this should be considered as uncertain, but with strong evidence it is around Manaus, AM, Brazil. We identified M.

justae from two major tributaries of the Rio Solimões, Rio Japurá and Rio Branco (tributary of Rio Negro), reinforcing the idea of Manaus as its type locality rather than João Pessoa, PB.

Material examined. Type: MCZ 21014, holotype, 45.2 mm SL, Brasil, J. M. S. Coutinho, 02-Ago1865. MZUSP 55752,12, 38.7–49,5 mm SL, Brasil, Roraima, Rio Branco, near to Viruá; 1°14’59”S, 61°50’22”W, J.N. Baskin 8 Dec 1993. Non-types: MZUSP 103127, 18, 42.8–49.7 mm SL, Amazonas, Japurá, Rio Japurá, Acanauaí, 01°50’00”S, 66°36’00”W, Expedição Permanente à Amazônia, 30 Nov–02 Dec 1997. MZUSP 55752, 12, 39.4– 49.2 mm SL, Roraima, Rio Branco, near to Viruá, J. N. Baskin, 0 8 Dec 1993. MCP 19661,6, 53.2–60.0 mm SL, Brasil, Pará Santarém, Rio Curuatinga, R.B. Oliveira, 0 1 Nov 1996. MCP 20546, 16, 51.9–63.4 mm SL, Brasil, Pará, Rio Tapajós, Alter do Chão, 02°31’00”S, 54°57’00”W, R.B. Oliveira, 0 3 Dec 1997. NUP 8106, 3 of 5, 54.5– 56.0 mm SL, Tocantins, Xambioá; Ribeirão Xambioá, tributary of Rio Araguaia, Rio Tocantins-Araguaia system, 06°24’27”S, 48°36’54”W, Gerpel, 22 Mar 2009. NUP 8136, 2 of 3, 47.7–55.1 mm SL, Tocantins, Xambioá, Rio Araguaia, tributary of Rio Tocantins, Rio Tocantins-Araguaia system; 06°11’11”S, 48°26’20”W; Gerpel, 0 9 Jul 2009. INPA 21489, 9, 32.1–51.5 mm SL, Caseara, Parque Estadual do Cantão, E.G. Ferreira, J. A. Zuanon & G. M. Santos, May 2000.