Moenkhausia mutum, Dagosta & Marinho, 2016

Dagosta, Fernando C. P. & Marinho, Manoela M. F., 2016, A new species of Moenkhausia Eigenmann (Characiformes: Characidae) from the rio Arinos basin, Brazil, Neotropical Ichthyology 14 (2), No. e 150052, pp. 1-7 : 2-6

Moenkhausia mutum , new species

urn:lsid:zoobank.org:act:BB985C10-AFC9-4130-BDFD-91679686FD7F

Holotype. MZUSP 117071 , 65.3 mm SL, Brazil, Mato Groso State, Nova Mutum, stream at road Nobres-Nova Mutum, on the intersection before Nova Mutum , tributary of rio dos Patos, rio Arinos drainage, rio Tapajós basin, 13º49’9”S 56º10’53.9”W, F. Dagosta, W. Ohara & V. Giovannetti, 14 Nov 2014.

Paratypes. All from Brazil, Mato Grosso, rio Arinos, upper rio Tapajós basin . MCP 31997, 4 , 36.0- 47.9 mm SL (3, 44.9- 47.9 mm SL) , MCP 32005, 1 , 61.8 mm SL (1), Diamantino, córrego Caju, at Caju locality, tributary of the rio Preto , 14º21’47”S 56º24’30”W , R. E. Reis, L . R. Malabarba & N. E. Pereira, 17 Jan 2002 . MCP 32057, 1 , 54.1 mm SL (1), Porto dos Gaúchos, igarapé Ribeirão Preto at MT-338 road, about 26 km SE of Porto dos Gauchos, 11º39’27”S 57º12’7”W , R. E. Reis, L . R. Malabarba & N. E. Pereira, 19 Jan 2002 . MCP 32098, 2 , 35.0- 42.1 mm SL (2), São José do Rio Claro, córrego about 4 km NW of São José do Rio Claro, at road to Nova Maringá , 13º25’51”S 56º44’53”W , R. E. Reis, L . R. Malabarba & N. E. Pereira, 18 Jan 2002 . MCP 32171, 1 , 38.1 mm SL (1), Tapurah , córrego at MT-338 road, about 46 km N of Tapurah, 12º23’14”S 56º41’54”W , R. E. Reis , R. L. Malabarba & E. H. Pereira, 19 Jan 2002 . MCP 44446, 1 , 35.3 mm SL, Nova Mutum, rio Criquiri, about 8 km of Nova Mutum , 13º48’11”S 56º9’23”W, F. Jerep, 24 Jan 2009 . MZUSP 61094 , 44 , 25.2-43.2 mm SL (1, 42.1 mm SL), Nova Mutum, rio Criquiri , tributary of Rio dos Patos, 13º48’10’’S 56º09’29’’W, F. C . T. Lima, M . R. Britto, W. B. Wosiacki, P. Gerhard, & E. G. Baena, 19 Fev 2000 . MZUSP 61119 , 31 , 26.3-50.4 mm SL (5, 45.2-50.4 mm SL), Nova Mutum, rio Criquiri , tributary of rio dos Patos, F. C . T. Lima, M . R. Britto, W. B. Wosiacki, P. Gerhard, & E. G. Baena, 13º50’60” S 56º10’60”W, 16 Feb 2000 . MZUSP 117072 , 21 , 40.0- 60.9 mm SL, (14, 51.1-60.9 mm SL), 3 c&s, 37.2-50.0 mm SL , CAS 238019 , 5 , 49.5-54.9 mm SL, same data as holotype . ZUEC 10059 , 6 , 52.7-56.8 mm SL (1, 58.5 mm SL), São José do rio Claro, rio Claro , upstream to the bridge at the MT- 235 road, 13º53’30”S 56º41’01”W, I. M. Fernandes & G. M. Alencar, 4-5 May 2007 .

Diagnosis. Moenkhausia mutum is distinguished from all congeners, except M. hemigrammoides , M. nigromarginata and Moenkhausia rubra by having intense diffuse dark pigmentation on the dorsal and anal fin-rays, especially in anteriormost rays and in the distal portion (vs. fins hyaliane or only with scattered chromatophores). It can be distinguished from M. rubra by the number of branched anal-fin rays 20-23, modally 21 (vs. 17-20, modally 19) and by having a vertically elongate humeral spot (vs. approximately rounded), from M. hemigrammoides by having pelvic fin intensely dark pigmentated (vs. hyaline), by the anal fin with a relative diffuse dark pigmentation (vs. presence of a black oblique line extending from the urogenital cavity to the tip of second or third branched anal-fin ray), and by lacking a well-defined black spot on the distal portion of the dorsal fin (vs. present), and from M. nigromarginata by lacking a series of longitudinal dark zigzag stripes on body formed by the concentration of dark chromatophores in the upper and lower portions of the exposed area of scales (vs. presence) and by having a vertically elongate roughly rectangular humeral spot surpassing the lateral line ventrally (vs. humeral spot approximately rounded, with an anteroventral projection not surpassing the lateral line ventrally).

Description. Morphometric data presented in Table 1. Body compressed, moderately deep. Greatest body depth slightly anterior to dorsal-fin origin. Dorsal profile of head convex from upper lip to vertical through posterior nostril and slightly convex from that point to tip of supraoccipital spine. Dorsal profile of body convex along predorsal region, straight along dorsal-fin base, straight or slightly convex from terminus of dorsal-fin base to adipose-fin origin, and concave from the latter point to origin of anteriormost dorsal procurrent caudal-fin ray. Ventral profile of head and body convex from tip of lower lip to pelvic-fin origin, slightly concave from that point to anal-fin origin, straight along anal-fin base, and concave from that point to origin of anteriormost ventral procurrent caudal-fin ray.

Jaws equal, mouth terminal. Premaxillary teeth in two distinct rows. Outer row with 3(5), 4*(17) or 5(8) tricuspid teeth. Inner row with 5*(30) pentacuspid teeth. Posterior tip of maxilla at vertical through middle of second infraorbital. Maxilla with 1(1), 2*(17) or 3(12) tricuspid teeth. Dentary with 4*(30) larger penta- to heptacuspid teeth followed by a series of 9(1) or 10(2) diminute conical teeth. Central median cusp in all teeth longer than lateral cusps. Branchiostegal rays 4(3). First gill arch with 2(2) or 3(1) gill rakers on hypobranchial, 8(3) rakers on ceratobranchial, 1(3) raker on intermediate cartilage, and 6(2) or 7(1) rakers on epibranchial.

Eyes with thick eyelid anteriorly. Scales cycloid, with 5-9 strongly marked radii from focus to posterior border, and conspicuous circuli anteriorly. Lateral line complete, with 31(1), 32(10), 33(11), 34*(7) or 35(1) perforated scales on longitudinal series. Longitudinal scale rows between dorsal-fin origin and lateral line 5*(29) or 6(1). Longitudinal scale rows between lateral line and pelvic-fin origin 3(5) or 4*(25). Scales along middorsal line between posterior tip of supraoccipital process and dorsal-fin origin 8(7), 9*(19) or 10(4). Horizontal scale rows around caudal peduncle 13(1) or 14(29). Base of anteriormost anal-fin rays covered by a series of 3-5 scales. Proximal half of caudal-fin lobes covered by small scales.

Supraneurals 3(1) or 4(2). Dorsal-fin rays ii*(30), 8(1) or 9(29). First dorsal-fin pterygiophore inserted posterior to neural spine of ninth(3) vertebra. Base of last dorsal-fin ray at vertical through base of first branched anal-fin ray. Pectoral-fin rays i*(30), 11(9), 12*(20) or 13(1). Pelvic-fin rays i*(30), 7*(30). Adipose fin present. Anal-fin falcate, with iv(1) or v(2), 20(3), 21*(12), 22(11) or 23(4) rays. First anal-fin pterygiophore inserted posterior to haemal spine of 16 th (3) vertebra. Principal caudal-fin rays i,9,8,i*(30). Caudal fin forked, lobes somewhat pointed, of similar size. Dorsal procurrent caudal-fin rays 11(2) or 12(1). Ventral procurrent caudal-fin rays 8(1) or 9(2). Total vertebrae 32(2) or 33(1): precaudal vertebrae 16(3) and caudal vertebrae 16(2) or 17(1). Color in alcohol. Overall ground coloration of head and body beige to light tan ( Fig. 1). Some specimens retaining guanine on infraorbital and opercular area and in some scales in the lateral portion of body. Dorsal portion of head and body dark. Dark chromatophores concentrated at upper and lower jaws. Scattered dark pigmentation more concentrated on first, fifth and sixth infraorbitals. Humeral blotch roughly rectangular and vertically oriented, overlying three or four scales vertically including the lateral line scale and three scales horizontally. Slight reticulated pattern on first three horizontal scale rows formed by concentration of dark chromatophores at the middle portions of scales. Scales of body with dark chromatophores concentrated at their posterior limit, more intense at the mid-dorsal scales. Overall body with scattered dark chromatophores gradually fading ventrally. A thin longitudinal line formed by subjacent dark pigmentation along horizontal septum starting slightly posterior to humeral blotch, extending onto caudal peduncle. Longitudinal dark stripe on body approximately one scale wide, extending from vertical through dorsal-fin origin to caudal peduncle, widening at caudal peduncle in some specimens, but not forming a peduncle-caudal spot. Caudalpeduncle spot absent. Scattered dark chromatophores along base of anal fin. Pectoral fin with dark chromatophores scattered along edge of lepidotrichia. Proximal half of dorsal, anal, and caudal fins with scattered dark chromatophores along edge of lepidotrichia. Distal half of dorsal, anal, and caudal fins with high concentration of dark chromatophores at interradial membranes, more intense in anteriormost dorsal and anal fin-rays. Some specimens with distalmost pelvic-fin rays with scattered dark chromatophores along edge of lepidotrichia and interradial membranes. Adiposefin base with scattered dark chromatophores, distal edge with intense dark pigmentation.

Color in life. Jaws and gular area orange. Dorsal portion of eye red in most specimens, brown in others. Lower portion of eye silvery. Dorsal portion of body dark brown. Infraorbitals, opercular area, middorsal and ventral portions of body silvery. Proximal half of dorsal fin orange. Some specimens with base of caudal-fin lobes orange. Dark pigmentation pattern of fins as described in Color in alcohol.

Sexual dimorphism. One male specimen (MZUSP 117072, 50.0 mm SL) presents very small bony hooks at the first to the thirteenth branched anal-fin ray, more developed in anteriormost ones. Hooks more concentrated at the posterior edge of the lepidotrichia.

Geographic distribution. Moenkhausia mutum is known from the rio Arinos drainage, tributary of rio Juruena, upper rio Tapajós basin, Mato Grosso State, Brazil ( Fig. 2 ).

Etymology. The specific name mutum is in allusion to the Brazilian popular name of the curassow birds of the genus Crax Linnaeus , which are typically dark colored, as well as the fins of Moenkhausia mutum . Also, the name refers to the Nova Mutum Municipality, the type locality, and where most of the type specimens were collected. A name in apposition.

Conservation status. Moenkhausia mutum is so far known from the rio Arinos drainage, the major tributary of rio Juruena, rio Tapajós basin, where it is widely distributed. Despite existing some riparian forest degradation for pasture in several sites where M. mutum occurs, it seems to not preclude the presence of the species in these areas. Therefore, Moenkhausia mutum would be classified as Least Concern (LC) following the International Union for Conservation of Nature (IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2014).

Figures

Fig. 2. Distribution map of Moenkhausia mutum in the upper rio Tapajós basin, Amazon basin. Type locality represented by white star.