Moenkhausia ischyognatha Petrolli & Benine, 2015, new species
Creators: name: Petrolli, Marina G.
name: Benine, Ricardo C.
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Characiformes
Characidae
Moenkhausia
Moenkhausia ischyognatha

description: 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.
description: Published as part of 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, pp. 401-420 in Zootaxa 3986 (4) on pages 404-407, DOI: 10.11646/zootaxa.3986.4.1, http://zenodo.org/record/234891