Moenkhausia ischyognatha, Petrolli, Marina G. & Benine, Ricardo C., 2015

Petrolli, Marina G. & Benine, Ricardo C., 2015, Description of three new species of Moenkhausia (Teleostei, Characiformes, Characidae) with the definition of the Moenkhausia jamesi species complex, Zootaxa 3986 (4), pp. 401-420 : 404-407

Moenkhausia ischyognatha , new species

( Figs. 2 a–b, 3a–b, 9c, Table 1 )

Holotype. MZUSP 117140, 45.5 mm SL, Mato Grosso, Gaúcha do Norte; Rio Curisevo, afluente rio Xingu, Porto Vitório, next ribeirão Kevuaieli, 13°02’05”S 53°25’19” W; C. Moreira, I. Landin, A. Datovo; 19 Oct 2004.

Paratypes. MZUSP 91182, 1, 47.2 mm SL, same data as holotype. LBP 15948, 37 (2 c&s), 39.8–56.9 mm SL, Mato Grosso, Canamara, Rio Culuene, 13°29’42”S, 53°04’58”W; C. Oliveira, M. Taylor, G.H.C. Silva, J.H.M. Martinez, 0 2 Aug 2012.

Diagnosis. Moenkhausia ischyognatha is readly distinguished from M. jamesi , M. justae , M. alesis , and M. sthenosthoma by its lower head depth (29.3–32.6% in SL vs. 34.0–43.2% in SL in the last four species). Additionally, it differs from M. jamesi and M. alesis by its lower body depth (37.0–43.0% in SL vs 44.3–52.3% in SL in M. jamesi , and 43.5–54.6% in SL in M. alesis ). It is also distinguished from M. alesis by the number of scale rows between lateral line and dorsal-fin origin (seven vs eight to nine in M. alesis ) and by the caudal-peduncle length (8.3–11.2% in SL vs. 3.8–7.5% in SL in M. alesis ). It is further distinguished from M. justae by the number of teeth in the maxilla (edentulous vs one tooth with three to five cusps in M. justae ), and by the number of cusps on the fourth dentary tooth (three to five vs six in M. justae ) ( Fig. 9 b, c). Moenkhausia ischyognatha is further distinguished from M. jamesi by the number of principal dentary teeth (four vs five in M. jamesi ) ( Figs. 9 a, c).

- M. ischyognatha (n=38) M. alesis (n= 32) M. sthenosthoma (n=97) Description. Morphometric data summarized in Table 1 . Largest specimen examined 55.9 mm SL. Body compressed and somewhat elongate. Greatest body depth at dorsal-fin origin. Dorsal profile of head straight to slightly convex; straight to slightly concave along the supraoccipital spine; slightly 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 ( Fig. 2 a) teeth with median cusp pronounced, the first two 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; edentulous maxilla. Dentary bearing four pentacuspidate teeth with central cusp longest followed by three to five distinctly small conical or tricuspidate teeth. First two or three dentary teeth from the symphysis with cusps arranged in a pronounced arch when examined from a dorsal view.

Dorsal-fin rays ii,9. Pectoral-fin rays i,12. Tip of pectoral fin extending 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,26(4), 27(10), 28(15), 29*(7), 30(2); caudal fin forked with i,9,8,i.

Scales cycloid. Lateral line with 35(1), 36*(17), 37(18), 38(1) perforated scales; Scale rows between lateral line and dorsal-fin origin 7. Scale rows between lateral line and midventral scale series 6(30) to 7*(8). Circumpeduncular scale rows 14*(2) and 15(36); Scale sheath along anal-fin base 7–15*, in single series, covering base of anteriormost rays. Small scales covering proximal two-third of caudal-fin lobes.

First gill arch with 12(1), 13(33)*, 14(2) gill rakers on lower limb and 8(1), *9(31), 10(5) on upper limb. Total vertebrae 31. Supraneurals 4.

Color in alcohol. Overall coloration 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 humeral mark to base of median caudal fin-rays. Irregularly shaped, humeral mark located over fourth to sixth lateral-line scales and extending vertically over four horizontal scale rows above and up to one horizontal scale row below lateral line. Paired fins and anal fin hyaline. Inconspicuous round dark spot at the base of the caudal-fin rays formed by few chromatophores. More well-preserved specimens may present a more conspicuous round caudal spot. Adipose with very few dark chromatophores ( Fig. 3 a–b).

Distribution. Moenkhausia ischyognatha occurs in the Rio Xingu basin, in Rio Culuene and Rio Curisevo ( Fig. 4 ).

Etymology. The species name ischyognatha is from Greek ischyo meaning strong, and gnatha meaning jaw, in reference to the strong musculature associated to the dentary, and robust teeth of the premaxilla and dentary, a diagnostic feature of the Moenkhausia jamesi species complex.

Figures

FIGURE 2. Moenkhausia ischyognatha, LBP 15948, 45.7 mm SL. (a) Left premaxilla (ventral view). (b) Left dentary (medial view). Scale bars: 0.5 mm.

FIGURE 3. Moenkhausia ischyognatha. (a) MZUSP 117140, holotype, 45.5 mm SL. (b) LBP 15948, 45.43 mm SL.

FIGURE 4. Partial map of South America indicating the distribuition of Moenkhausia jamesi species complex and M. justae. Red circle = M. jamesi; Blue circle = M. ischyognatha; Orange circle = M. alesis; Light blue circle = M. sthenosthoma; Yellow circle = M. justae.

FIGURE 9. Dentary of Moenkhausia jamesi species complex. (a) M. jamesi, MZUSP 49507, 54.0 mm SL; (b) M. justae, INPA 21489, 47.0 mm SL; (c) M. ischyognatha, LBP 15948, 48.2 mm SL; (d) M. alesis, INPA 48444, 50.4 mm SL; (e) M. sthenosthoma, LBP 19956, 46.0 mm SL; and (f) M. sthenosthoma, LBP 19958, 63.4 mm SL. Scale bars = 1 mm.

Tables

TABLE 1. Morphometric data for Moenkhausia ischyognatha sp. n., Moenkhausia alesis sp. n., and Moenkhausia sthenosthoma sp. n. N includes holotype. Range includes holotype and paratypes.

	Holotype	Range	Mean	Holotype	Range	Mean	Holotype	Range	Mean
Standard Length (mm)	45.5	39.8–56.9		52.6	44.7–57.4		56.0	22.3–63.4
Percentage of Standard Length Greatest depth	38.5	37.0–43.0	40.5	45.8	43.0–54.6	48.1	49.6	38.7–51.3	44.4
Snout to dorsal-fin origin	50.6	48.7–52.8	50.3	51.1	47.5–54.1	51.5	52.3	48.7–54.0	51.2
Snout to pectoral-fin origin	27.2	25.0–29.1	26.8	26.7	24.4–29.9	27.2	27.3	25.5–34.3	29.2
Snout to pelvic-fin origin	49.4	47.2–51.9	49.2	49.8	45.8–53.9	50.0	51.3	46.8–53.1	50.0
Snout to anal-fin origin	67	64.3–69.6	66.5	67.2	61.9–70.9	67.3	67.7	61.5–69.6	65.9
Caudal-peduncle depth	11	10.4–12.0	11.2	11.8	10.6–13.0	11.9	12.1	9.2–12.8	11.4
Caudal-peduncle length	8.5	8.3–11.2	9.6	7.3	3.8–7.5	5.6	7.7	6.3–10.2	8.1
Pectoral-fin length	22.9	17.8–23.5	21.3	23.6	17.6–25.1	21.8	22	16.1–24.7	21.7
Pelvic-fin length	19.9	16.0–19.9	17.8	20.6	16.7–20.6	18.2	19.3	14.7–20.9	18.2
Dorsal-fin length	31.2	25.6–32.4	29.8	34	28.1–35.6	33.0	34.4	27.7–37.5	34.2
Dorsal-fin base	15.8	13.9–16.3	14.9	16.3	13.5–17.6	15.9	15.9	14.4–18.6	16.5
Anal-fin length	17.8	12.1–18.2	15.9	17.2	13.4–19.4	16.9	20.1	14.9–23.1	20.4
Anal-fin base	33	29.9–34.3	31.8	35.4	32.1–39.8	36.2	36.6	33.1–38.4	35.6
Eye to dorsal-fin origin	36.2	34.7–39.1	36.8	38.1	35.8–40.8	38.8	39.6	33.9–51.2	37.1
Dorsal-fin origin to caudal-fin origin Head length	55.4 26.5	53.2–59.0 24.4–27.4	56.0 25.7	56.7 25.2	49.2–58.6 23.2–27.0	58.6 25.0	55.4 25	51.5–58.6 22.9–29.5	54.9 26.2
Head depth	30.4	29.3–33.3	31.2	36.9	35.9–43.2	39.1	38.0	33.5–40.1	36.2
Percentage of Head length Snout length	30.1	25.5–33.5	28.6	29.6	22.6–34.1	29.4	25.1	20.2–31.2	25.6
Maxillary length	34	31.8–37.6	34.4	35.8	33.7–41.3	36.9	37.1	31.1–39.8	35.6
Horizontal orbital diameter	41.9	39.9–47.0	43.2	43.2	36.9–45.3	41.7	44.4	41.7–49.6	46.3
Least interorbital width	36.8	35.3–39.3	37.3	39.9	37.6–48.6	42.1	39.2	33.3–49.2	39.6