Myloplus nigrolineatus, Ota & Machado & Andrade & Collins & Farias & Hrbek, 2020

Ota, Rafaela Priscila, Machado, Valéria Nogueira, Andrade, Marcelo C., Collins, Rupert A., Farias, Izeni Pires & Hrbek, Tomas, 2020, Integrative taxonomy reveals a new species of pacu (Characiformes: Serrasalmidae: Myloplus) from the Brazilian Amazon, Neotropical Ichthyology (e 190112) 18 (1) : -

Myloplus nigrolineatus , new species urn:lsid:zoobank.org:act:045EB69A-EC87-4D58-AF6D-0E00AF1259BD

( Figs. 1–4 ; Tab. 1)

Myloplus asterias —Machado et al., 2018: 8 ( Brazil, rio Nhamundá, fig. 3d).

Myloplus sp. — Zeinad, Prado, 2012: 148 ( Brazil, rio Itapará, tributary of rio Branco, photo).

Myloplus aff. asterias —Morales et al., 2019: 6, 9 ( Brazil, Tucuxi lake, rio Purus, Tab. 2, fig. 2, 3 and 4).

Holotype. INPA 54773 , 1 , x-rayed, 221.9 mm SL, CTGA 15249 (GenBank accession MG752242 ), Brazil, Amazonas State , ca. 60 km south of Manaus , lago Tracajá , tributary of rio Juma, rio Amazonas basin, 3°41’15”S 59°57’01”W, 22 Nov 2014, V. N. Machado.

Paratypes. All from Brazil. Amazonas State : INPA 54774 , 3 , x-rayed, 203.2–231.7 mm SL , CTGA 15246 ( MG752239 ), 15247 ( MG752240 ), and 15250 ( MG752243 ), collected with holotype. Rio Negro basin : INPA 925 , 6 , 182.6 – 237.7 mm SL, Novo Airão, ilha de Tamaquare , rio Negro, 2°53’00”S 60°30’59”W, 14 Oct 1979 , M. Goulding; INPA 22326 , 9 , 145.5 – 197.5 mm SL, Novo Airão, rio Negro , Anavilhanas, 2°43’05”S 60°45’16”W, Jan 1981 , M. Goulding; INPA 23312 , 2 , 182.0– 199.1 mm SL, São Gabriel da Cachoeira , lago Mabi, 0°55’49”N 66°47’37”W, 22 Feb 2014 , V. N. Machado ; INPA 52505 , 3 , 182.3 – 202.7 mm SL , CTGA 12278 ( MG752202 ), 12329 ( MG752209 ), and 12331 ( MG752211 ), Barcelos, rio Negro nearby Barcelos, 0°56’56”S 62°55’44”W, 20 Feb 2013 , V. N. Machado ; INPA 52506 , 3 , 159.9 – 193.4 mm SL , CTGA 12323 ( MG752203 ), 12325 ( MG752205 ), and 12327 ( MG752207 ), same data as INPA 52505 ; INPA 53281 , 2 , skel., 170.7–180.3 mm SL, Manaus, rio Negro nearby Manaus, ca. 3°08’S 59°54’W, 18 Apr 2017 , local fisherman; INPA 54770 , 1, 181.2 mm SL, Manaus, rio Puduari , Parque Estadual do Rio Negro, 2°23’57”S 61°21’08”W, 21 Apr 2005 , F. Mendença, F. Pires & M. Picasso. Rio Maués-Açu basin : INPA 34810 , 2 , 172.5 – 174.5 SL, Maués, rio Parauari , community Monte Sinai, 4°21’28”S 57°35’54”W, 31 May 2005 , R. R. de Oliveira & W. Pedrosa. Rio Purus basin : INPA 58772 , 1, 189.3 mm SL, Manicoré, lago Tapauá, rio Purus , 5°43’14”S 63°17’12”W , D. Castanho & A. G. Bifi. Rio Urubu : INPA 58873 , 1, 155.9 mm SL, Itacoatiara, lago Serpa, tributary of rio Urubu , 3°05’11”S 58°30’25”W, 13 Jul 2018 , R. G. Amaral da Silva. Mato Grosso, rio Madeira basin : INPA 56750 , 1, 104.5 mm SL , CTGA 15231 ( MG752238 ), Aripuanã, confluence of rio Branco and rio Aripuanã, 9°46’41”S 59°23’53”W, 9 Dec 2014 , V. N. Machado. Pará, rio Nhamundá : ANSP 207984 , 2 , 180.0- 205.8 mm SL ; INPA 46320 , 6 , 1 x-rayed, 178.0– 198.8 mm SL , CTGA 14469 to 14474 ( MG752220 to MG752225 ), Nhamundá, community Barão, 1°41’27”S 57°25’20”W, 22 Nov 2013 , V. N. Machado & R. A. Collins ; INPA 46321 , 1, 125.8 mm SL , CTGA 14365 ( MG752214 ), Nhamundá, community Chave, 1°40’29”S 57°28’36”W, 25 Nov 2013 , V. N. Machado & R. A. Collins. Rio Tapajós : INPA 23446 , 2 , 160.0– 161.8 mm SL , CTGA 15393 ( MG752246 ) and 15401 ( MG752249 ), Itaituba, 5°37’46”S 57°15’11”W, 10 Oct 2015 , V. N. Machado. Rio Tocantins : INPA 57801 , 2 , 149.3 – 167.4 mm SL , CTGA 5765 ( MG752188 ) and 5766 ( MG752189 ), Tucuruí, 3°48’29”S 49°40’17”W, 6 Nov 2009 , V. N. Machado. Roraima, rio Branco basin : INPA 46279 , 4 , 172.6 – 197.1 mm SL , CTGA 12201 ( MG752197 ), 12202 ( MG752198 ), 12204 ( MG752199 ), and 12205 ( MG752200 ), Rorainópolis, left bank of rio Branco , 0°58’08”S 61°54’02”W, 17 Feb 2013 , V. N. Machado ; INPA 54772 , 1, 179.2 mm SL, Caracaraí, beach at rio Água Boa do Univini , Serra da Mocidade, 1°11’N 61°41’W, 9 Apr 2017 , D. A. Bastos.

Non-types. Amazonas, rio Juruá basin: INPA 58915 , 4 , 147.4 – 164.6 mm SL , CTGA 16865 ( MN702903 ), 16866 ( MN702887 ), 16868 ( MN702901 ), 16869 ( MN702902 ), Carauari , lago Pauapixuna, 4°49’11”S 66°50’54”W, 1 Mar 2018 , V. N. Machado. Rio Negro basin : INPA 895 , 3 , 190.3 – 218.2 mm SL, Santa Isabel do Rio Negro , rio Maraiuá, ca. 0°14’S 65°10’W, 14 Oct 1979 , M. Goulding; INPA 931 , 10 , 160.7 – 208.2 mm SL, Santa Isabel do Rio Negro , igarapé Ibará, ca. 0°11’S 65°55’W, 20 Mar 1980 , M. Goulding; INPA 937 , 6 , 166.7 – 194.5 mm SL, São Gabriel da Cachoeira , ca. 0°03’S 68°07’W , Apr-May 1980, M. Goulding; INPA 22194 , 9 , 144.1 – 235.7 mm SL, Barcelos , rio Arirará, close to the confluence with rio Negro, ca. 0°30’S 63°32’W, Feb 1980 , M. Goulding. Rio Uatumã basin : INPA 46058 , 1, 119.6 mm SL, Balbina , cachoeira Terceira Queda , rio Pitinga, Amazonas, 1°07’00”S 59°36’00”W, 26 Sep 1996 , V. Garcia. Rio Javari: INPA 58914 , 3 , 161.3 – 185.7 mm SL , CTGA 17492 ( MN702891 ), 17493 ( MN702892 ), 17494 ( MN702893 ), Atalaia do Norte , ca. 4°20’S 70°13’W, 1 Oct 2018 , V. N. Machado.

Diagnosis. Myloplus nigrolineatus can be easily diagnosed from all congeners by highly concentrated dark chromatophores on the lateral-line scales, resulting in a markedly, dark pigmentation along the lateral line. Additionally, the new species can be distinguished from M. arnoldi , M. lobatus , M. lucienae , M. planquettei , M. rhomboidalis , M. schomburgkii , and M. zorroi by having 25–29 branched dorsal-fin rays (vs. 18–24). It can be distinguished from M. ternetzi by the presence of a symphyseal pair of conical teeth posterior to the main row of dentary (vs. absence); and from M. asterias , M. levis , M. rubripinnis , M. taphorni , M. tiete , M. torquatus , and M. tumukumak by having 89–114 lateral line scales from supracleithrum to end of hypural plate (vs. 56–89) and 98–120 total perforated lateral line scales (vs. 59–97).

Description. Morphometric data are presented in Tab. 1. Body laterally compressed, overall aspect of body elliptical, greatest body depth at vertical through dorsal-fin origin. Dorsal profile of head convex from mouth to vertical through anterior nostril, slightly concave to straight from this point to tip of supraoccipital process, and convex from this point to dorsal-fin origin. Dorsal-fin base slightly to moderately convex. Body profile almost straight from dorsal-fin insertion to adipose-fin origin. Adipose-fin base gently convex. Head with ventral half of opercle approximately twice as large as dorsal half, with posterior margin surrounded by thin opercle membrane, covering two scales horizontally at point of greatest head length.

Ventral profile of head and body convex. Ventral keel composed by 23(1), 24(3), 25(1), 26(2), 27(10), 28*(7), 29(14), 30(5), or 32(1) prepelvic spines; plus 8(8), 9*(13), 10(14), 11(5), or 12(3) postpelvic spines; followed by 5(1), 6(6), 7*(13), 8(12), 9(10), or 10(1) paired spines around anus. Total spines composing ventral keel 39(2), 40(1), 41(1), 42(2), 43(6), 44*(2), 45(9), 46(13), 47(2), 48(5), or 49(1). Caudal peduncle relatively short, ventral profile slightly concave.

Mouth terminal to slightly upturned. Two rows of molariform premaxillary teeth, 5*(45) teeth in lingual row, and 2*(45) in labial row. First and second tooth in labial row interspaced by gap from teeth of lingual row. Premaxillary teeth 1–3 of lingual row with moderately sharp edges. Dentary with 5*(10) or 6(28) molariform teeth gradually decreasing posteriorly in size. Pair of conical symphyseal teeth posterior to main row of teeth, with cutting edge on anterior margin. Maxillary edentulous.

Ascending premaxillary process elongate, similar width from base to distal tip, with distal tip gently pointed, and moderately inclined relative to lateral premaxillary process. Premaxillary lacking interdigitations at symphysis and strongly attached on mesethmoid. Lateral premaxillary process rectangular, with dorsolateral process extending beyond last tooth, with concavity for maxillary insertion. Three replacement teeth trenches on premaxillary. Dentary rectangular, slightly arched with three rounded or oval replacement tooth-trenches, posterior more elongate. Four bony lamellae at symphysis. Anguloarticular well developed and articulated with quadrate by thin cartilage. Retroarticular contacting posteroventral portion of dentary. Coronomeckelian elongate.

Scales cycloid, minute, and numerous. Perforated scales from supracleithrum to hypural-plate end 89(3), 90(7), 91(2), 92(1), 93(7), 94(1), 95(5), 96*(1), 97(1), 98(1), 99(4), 100(4), 101(1), 102(2), 106(1), 107(1), 108(1), 110(1), or 114(1); total perforated scales on lateral line till base of median caudal-fin rays 98(11), 99(5), 100(5), 101(2), 102(3), 103(2), 105(4), 106(1), 107(2), 108*(2), 110(2), 112(3), 113(1), 119(1), or 120(1). Scale rows above lateral line 50(1), 52(6), 53(5), 54(7), 55(8), 56(6), 57*(5), 58(2), 59(2), or 60(3). Scale rows below lateral line 48(3), 49(7), 50(3), 51(3), 52(4), 53(6), 54(2), 55*(5), 56(3), 57(3), 58(3), or 59(2). Circumpeduncular scales 32(1), 33(7), 34(5), 35(7), 36(10), 37*(7), 38(6), 39(1), or 40(1).

Dorsal fin preceded by strong, forward-oriented spine. Dorsal-fin rays ii-iii, 25(13), 26*(14), 27(12), 28(5), or 29(1). Dorsal-fin origin slightly posterior to vertical through pelvic-fin origin, distal margin variable (see Sexual dimorphism). Adipose-fin distal margin round to sub-rectangular. Pectoral-fin rays i, 11(1), 12(2), 13(6), 14(19), 15*(15), or 16(2); distal margin convex, with anterior rays longest. Pelvic-fin rays i, 6*(33) or 7(10) with distal margin convex, anterior rays slightly longest, not reaching vertical through anal-fin origin. Anal-fin rays iii-iv, 33(3), 34(7), 35(8), 36*(15), 37(9), or 38(3). Caudal fin forked with both lobes similar in size.

First branchial arch with 26(1), 27(6), 28(6), 29(4), 30*(14), 31(6), 32(4), or 33(1) total gill rakers; upper branch with 12(15), 13*(12), 14(13), or 15(2) rakers; lower branch with 13(1), 14(7), 15(11), 16*(19), 17(3), or 18(1) rakers; 1(43) at cartilage between cerato- and epibranchial. Gas bladder two-chambered, total length 41–50% SL, with extrinsic muscle thin and poorly-developed. Anterior chamber smaller, cylindrical, horizontally positioned, with length 15–19% SL. Posterior chamber larger, somewhat conical, posteriormost region narrower not very contracted, with length 26-32% SL, curved downward, with long appendix on distal end (2–3% SL).

Neurocranium massive, deep and triangular in lateral view ( Fig. 2A ). Mesethmoid short, pointed and triangular anteriorly in dorsal view ( Fig. 2B ), dorsal profile convex in lateral view. Lateral wings of mesethmoid elongate. Dorsal portion of lateral ethmoid reaching anteroventral surface of frontal, lateral wing elongated, ventrally directed. Vomer excluded from ventral limit of olfactory fossa. Olfactory fossa circular, poorly developed. Nasal narrow, elongate. Parasphenoid long and gently curved ventrally ( Fig. 2A ), with very reduced ventral keel on anterior portion, ventral aperture arising two thin projections nearly parallel to each other through ventral margins of prootic and basioccipital. Frontal rectangular, relatively short, approximately 30% of neurocranium length. Epiphyseal bar dividing cranial fontanel; anterior rounded to slightly oval, posterior narrow somewhat triangular, almost closed ( Fig. 2B ). Neurocranium with moderate concavity at frontal bone ( Fig. 2A ). Pterosphenoid laminar, laterally articulated to sphenotic. Orbitosphenoid possessing two laterally compressed bony lamellae, anterior upturned, posteroventral process projecting ventrally with interdigitations on ventral margin not reaching parasphenoid ( Fig. 2A ). Prootic retangular, with anterodorsal circular aperture. Sphenotic with concave ventral margin, with pointed lateral spine for insertion of dilatator operculi. Parietal with dorsal surface sculptured by many grooves, posterior plate gradually narrower. Intercalar diminute, posteroventrally situated. Pterotic triangular with two-pointed downward directed processes. Epoccipital with lateral arm extending towards posterior margins of parietal and pterotic, separating posttemporal fossa into dorsal and ventral portions. Basioccipital forming entire ventral surface of saccular capsule. Exoccipital with large lagenar capsule. Supraoccipital spine long, well-developed, dorsal profile convex ( Fig. 2A ).

Infraorbital series well developed. Antorbital robust, with base larger than tip. Six infraorbitals forming semi-circle, leaving a small naked area on cheeks, not covering lateral surface of vertical arm of preopercle. Infraorbital 6 with “Y” shaped laterossensory channel. Supraorbital somewhat oval and narrow with slightly convex anteroventral margin, not contacting infraorbital 6. Orbital region overall wide ( Fig. 2A ).

Total vertebrae 38(3) or 39*(1). Abdominal vertebrae 14(2) or 15*(2). Caudal vertebrae 20*(4). Vertebrae between last dorsal-fin pterygiophore and first anal-fin pterygiophore 6(2) or 7*(2). Supraneurals 5*(2) or 6(2).

Color in alcohol. Ground coloration gray to pale-yellow, head and body darker dorsally. Lateral line scales with melanophores forming dark stripe along flanks

( Figs. 1 , 3 ); melanophores vertically elongate, similar to stitches ( Fig. 4F ). Posterior half of scales well-pigmented, anterior half pale. Males with concentration of small dark spots, forming irregular blotches over the body, most dispersed above the lateral line. Light blotches scattered on flanks, predominantly concentrated above lateral line ( Figs. 4E, F ). Mandibular and gular regions, first four infraorbitals, and cheek gap light brown. Eye with broad dark transversal bar crossing pupil (not discernible in specimens retained for a long period in formalin) ( Fig. 4 ). Dorsal, anal, pelvic and caudal fins overall somewhat hyaline, becoming darker towards fin margins. Pectoral fin light to dark brown. Caudal fin with dark and diffuse distal band.

Color in life. Overall body coloration varying from silvery to plumbeus, with orange blotches scattered on flanks. Dorsal profile of head and inferior half of opercle with high concentration of melanophores. Fins uniformly hyaline or light yellow with scattered dark chromatophores along interradial membranes. Males during breeding period with anterior lobe of anal fin orange to intense red; with irregular-shaped orange to blood-red blotch on posterior half of head to supracleithrum region, situated in opercular area, and near pectoral-fin origin. Males during breeding period also possessing dark, irregularly shaped and distributed blotches, more concentrated along dorsal half of flanks ( Figs. 4E, F ). Females during breeding period with orange and dark gray irregularly shaped blotches scattered on flanks ( Fig. 4B ).

Sexual dimorphism. Myloplus nigrolineatus presents the typical sexual dimorphism pattern of other Myloplus species, with males possessing an additional anal-fin lobe centered on 14th or 15th branched ray ( Figs. 3A ; 4C–F ), the presence of stiff hooks laterally curved on distal-most lepidotrichia segment of anal-fin branched rays, and by the presence of ossified protuberances on anal-fin branched rays forming additional lobe (absent in females). Male specimens additionally present thin, long filaments extending branched dorsal-fin rays (absent in females; Figs. 4E, F ), and display darker background coloration and more intense colors ( Figs. 3 , 4 ), with scattered dark and orange blotches more conspicuous than in females (see Color in life). Females have very rigid unbranched anal-fin rays, with first eight to ten rays extremely elongate forming a falcate margin ( Figs. 3B ; 4A, B ). Representatives of Myloplus nigrolineatus in the breeding season show remarkable coloration with intense grayish-orange to blackish-red colors ( Figs. 4E, F ), while in the non-breeding season these colors are faint ( Figs. 4B, C ). Dissected females collected in October (INPA 895) and April (INPA 931 and INPA 937) had ripe gonads.

Geographical distribution. Myloplus nigrolineatus is widespread in the Amazon basin, occurring in the Negro, Branco, Nhamundá, Purus, Madeira, Tapajós, Tocantins, and Uatumã rivers ( Fig. 5 ). In whitewater rivers with high sediment loads such as the Madeira, Branco, and Purus, Myloplus nigrolineatus was only captured in tributaries with black- or clearwater (see Ecological notes).

Ecological notes. The species inhabits slow-flowing habitats such as backwaters and lakes, feeding mainly on aquatic and terrestrial plants (Goulding, 1980). Of the collection localities, the Aripuanã, rio Água Boa do Univini (rio Branco), Nhamundá, Tapajós, Tocantins, and Uatumã rivers are clearwater rivers chemically characterized by a low concentration of suspended sediments, dissolved minerals and humic compounds (Crampton, 2011), while the rio Negro basin, rio Jutaí, Pauapixuna lake (rio Juruá), Tapauá lake (rio Purus), Serpa lake (rio Amazonas), and rio Maués-Açu are extremely acidic oligotrophic blackwaters ( Sioli, 1984; Goulding et al., 1988). The Tracajá lake (holotype locality) is also a blackwater system that has its headwaters in the Purus- Madeira interfluvium and like other blackwater rivers, is of low sediment load and low pH. These blackwater environments are inhospitable to certain species of fish ( Wallace, 1889; Roberts, 1972; Goulding et al., 1988; Araújo-Lima, Goulding, 1997; Saint-Paul et al., 2000; Crampton, 2011; Lima, Ribeiro, 2011).

Etymology. The epithet nigrolineatus , from the Latin nigro meaning black, and lineatus meaning lined, an allusion to the black, pigmented lateral line. An adjective.

Conservation status. Myloplus nigrolineatus is a common and naturally abundant species, widely distributed within black- and clearwater Amazonian rivers in Brazil. As no specific threats were detected, M. nigrolineatus can be tentatively categorized as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2017).

Molecular results: The 29 COI barcode sequences generated in this study were deposited in GenBank under the accession codes MN702885–MN702913. Combined with the 377 sequences from Machado et al. (2018) the alignment comprised 406 individuals from 32 morphologically assigned species (https://github.com/legalLab/ publications). After alignment and trimming, the matrix was 621 bp with a median sequence length of 621 bp of non-gap characters (min. = 477 bp; mean = 605 bp), and comprised 161 unique haplotypes. Myloplus nigrolineatus was represented by 68 sequences (20 unique haplotypes) from 18 unique sampling localities.

The four species discovery methods partitioned the total dataset into between 39 (localMinima) and 48 (GMYC) lineages (mPTP = 40; bGMYC = 44; Fig. 6 ). In Myloplus there were between 25 (localMinima) and 29 (GMYC) lineages (mPTP = 26; bGMYC = 28; Fig. 6 ). All four methods recovered M. nigrolineatus as a distinct lineage with GMYC partitioning the species into two further groups. Myloplus nigrolineatus had a Bayesian posterior probability of monophyly of 1 in the maximum clade credibility consensus tree, and was found as sister taxon to a lineage of Myloplus from the Tapajós River (posterior probability 0.53). Mean genetic distance to the closest non-conspecific of Myloplus nigrolineatus was 2.1% uncorrected p distance (min. = 1.8%; max. = 2.4%), and 2.5% TrN+ Γ corrected distance (min. = 2.1%; max. = 3.1%).

Remarks. Myloplus asterias is the most similar looking congener of M. nigrolineatus , sharing with the new species the general body shape and an elevated number of branched dorsal-fin rays (25–29). However, both species can be diagnosed by the number of total lateral line scales (98–120 in M. nigrolineatus vs. 79–97 in M. asterias ). Myletes ellipticus

Günther, 1864, Myleus gurupyensis Steindachner, 1911 , Myloplus schulzei Ahl, 1938 , and Tometes maculatus Amaral Campos, 1944 were considered by Jégu (2003) junior synonyms of Myloplus asterias . Later, Jégu et al. (2004) redescribed Myloplus asterias , and designated its lectotype (ZMB 23686) and paralectotypes (ZMB 3636, 3637, and BMNH 1971.5.10.61, Fig. 7 ) from Guyana, Essequibo River. Through our analyses of the type material of all these species, we could confirm the number of total lateral line scales (87– 88 in M. asterias , 91 in Myletes ellipticus , 90 in Myleus gurupyensis , 92 in Myloplus schulzei , and 79 in Tometes maculatus ) being lower than that of M. nigrolineatus . Those counts fit in the range of dorsal-fin rays of Myloplus asterias as defined herein, corroborating their synonymy as proposed by Jégu (2003), and, therefore, not representing available names for Myloplus nigrolineatus .

Figures

FIGURE 1 | Myloplus nigrolineatus, INPA 54773, holotype, 221.9 mm SL, male, lago Tracajá, tributary of rio Juma, ca. 60 km south of Manaus, Amazonas State, Brazil.

FIGURE 2 | Osteology of the head of Myloplus nigrolineatus, INPA 53281, 180.3 mm SL, Manaus, rio Negro nearby Manaus: A. lateral view; B. dorsal view. afo, anterior fontanel; epi, epiotic; eth, lateral ethmoid; fro, frontal; int, interopercle; io, infraorbitals; max, maxillary; mth, mesethmoid; nas, nasal; neu, neural; ope, opercle; oph, orbitosphenoid; par, parietal; pfo, posterior fontanel; pmx, premaxillary; pre, preopercle; psh, parasphenoid; ptr, pterotic; pts, pterosphenoid; qu, quadrate; so, supraorbital; sub, subopercle; sup, supraoccipital; vom, vomer.

FIGURE 3 | Myloplus nigrolineatus, paratypes, INPA 23312, lago Mabi, São Gabriel da Cachoeira, Amazonas State, Brazil. A. 199.1 mm SL, male; B. 182.0 mm SL, female.

FIGURE 4 | Freshly collected Myloplus nigrolineatus with different color patterns. A. INPA 23312, 182.0 mm SL, female, lago Mabi, São Gabriel da Cachoeira, Amazonas; B. INPA 53281, 170.7–180.3 mm SL, female, rio Negro nearby Manaus, Amazonas; C. INPA 23446, 160.0 mm SL, male, tissue voucher CTGA 15401, Tapajós Itaituba, Pará; D. INPA 46279, 172.3 mm SL, male, tissue voucher CTGA 12201 (GenBank accession MG752197), rio Branco, boundary between Caracaraí and Rorainópolis, Roraima; E. INPA 58772, 189.3 mm SL, male, rio Purus, Tapauá, Amazonas; F. INPA 52505, 186.4 mm SL, male, tissue voucher CTGA 12329 (MG752209), rio Negro nearby Barcelos, Amazonas.

FIGURE 5 | Map of northern South America, showing the distribution of Myloplus nigrolineatus. Black star represent the type locality, black circles the paratypes, yellow the non-types localities, and the gray represents the locality of exemplars used exclusively in the molecular analyses (without voucher in museums).

FIGURE 6 | Chronogram (maximum clade credibility consensus of 3,000 post burn-in posterior trees) of Myloplus and related genera constructed in BEAST using DNA barcode sequence data. Comprises 161 unique haplotypes (total 406 sequences), with the number of haplotypes represented by each tip in parentheses, followed by the drainages where these haplotypes were recovered. Species discovery congruence for four methods (localMinima, mPTP, bGMYC and GMYC) is presented in colored columns. Branch support (Bayesian posterior probability) of ≥95% is shown with an orange node label. Myloplus nigrolineatus is highlighted with a green box.

FIGURE 7 | Myleus asterias, paralectotypes, BMNH 1971.5.10.61-2, Essequibo River, Guyana. Photo: Kevin Webb. https://data.nhm.ac.uk/ object/7b7ff23f-df96-47e2-8f6b-dcf25ca45984/1572393600000