George Mattox
Rafaela Priscila Ota rafaelapota@gmail.com
The authors declare no competing interests.
The material was collected under the permanent licenses of Izeni Pires Farias (11325-1) and Lucia Helena Rapp Py-Daniel (11561-1).
Pacus of the genus
Pacus do gênero
The accessibility of molecular techniques to taxonomists has increased the number of species descriptions that include molecular data (
Osteological features included in the Description section were analyzed in two skeletonized (skel) specimens (INPA 53281), and from two x-rayed specimens (INPA 54474-holotype, and INPA 46320). Dried skeletons were prepared with addition of dermestid beetle larvae and x-ray radiographs taken in Faxitron® specimen radiography system LX-60 (
Counts are followed by their frequency in parentheses, with an asterisk indicating the count observed in the holotype. In the comparative material list, the number of specimens of each lot is given first, followed by those skeletonized or x-rayed, by tissue voucher number (CTGA), and finally by GenBank accession number in parentheses. Information on sexual dimorphism, including sex and breeding condition of the dissected material was determined according to
Institutional abbreviations are ANSP, Academy of Natural Sciences, Philadelphia; BMNH, Natural History Museum, London; INPA, Instituto Nacional de Pesquisas da Amazônia, Manaus; MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo; NUP, Coleção Ictiológica do Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (Nupélia), Maringá; NMW, Naturhistorisches Museum, Zoologische Abteilung, Fische, Vienna; ZUFMS, Coleção Zoológica da Universidade Federal de Mato Grosso do Sul, Campo Grande.
For the newly collected tissue samples, collection, storage, DNA isolation, PCR, sequencing and assembly protocols followed
urn:lsid:zoobank.org:act:045EB69A-EC87-4D58-AF6D-0E00AF1259BD
(
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 (
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 (
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).
Holotype
N
Range
Mean
SD
Standard length (mm)
221.9
44
145.7-237.7
-
-
Percents of standard length
Body depth
63.8
44
58.7-71.0
64.9
3.32
Head length
29.9
44
26.0-32.0
28.7
1.32
Supraoccipital process
31.7
44
26.3-33.2
30.1
1.68
Predorsal length
57.6
44
53.8-58.9
56.7
1.36
Dorsal-fin base length
37.1
44
33.4-40.1
36.7
1.35
Interdorsal length
7.4
44
5.8-9.5
7.5
0.83
Adipose-fin base length
4.2
44
3.7-5.7
4.4
0.43
Caudal-peduncle depth
9.7
44
8.4-10.7
9.6
0.47
Anal-fin base length
34.2
44
29.6-37.8
34.1
1.91
Preanal length
79.2
44
75.0-90.2
78.9
2.33
Prepelvic length
59.5
43
57.3-63.0
60.0
1.54
Prepectoral length
31.9
44
28.2-32.8
30.5
1.10
Pelvic-anal distance
22.6
43
18.6-23.5
21.4
1.33
Pelvic-pectoral distance
28.4
43
26.8-34.5
30.6
1.76
Width of peduncle
6.0
44
4.1-6.2
5.1
0.57
Pectoral-fin length
22.6
44
21.3-25.2
23.2
0.94
Pelvic-fin length
13.6
42
11.3-14.9
13.5
0.87
First anal-fin lobe length
18.0
42
13.0-41.7
25.4
9.02
Second anal-fin lobe length
13.6
24
10.9-17.8
13.7
1.89
Dorsal-fin length
19.6
41
16.6-29.7
21.9
2.82
Dorsal- to anal-fin origin
67.5
44
59.7-73.8
67.8
3.48
Dorsal-fin end to anal-fin origin
47.0
44
43.1-52.8
47.9
2.59
Dorsal- to anal-fin end
21.2
44
17.3-23.9
20.5
1.29
Percents of head length
Snout length
25.6
44
23.5-32.2
27.6
2.16
Interorbital width
51.8
44
47.1-57.8
52.4
2.16
Width head
58.1
43
52.3-65.5
59.4
2.56
Postorbital distance
38.7
44
32.0-41.8
36.7
2.28
Fourth infraorbital width
12.0
44
9.8-14.7
11.9
1.01
Eye vertical diameter
28.9
44
27.6-35.3
30.7
1.79
Mouth length
13.1
44
10.5-16.6
13.4
1.37
Third infraorbital width
11.7
44
9.7-14.8
12.1
1.05
Cheek gap width
10.8
44
7.6-14.9
10.7
1.49
Mouth width
33.3
44
30.8-39.6
34.0
1.86
The four species discovery methods partitioned the total dataset into between 39 (localMinima) and 48 (GMYC) lineages (mPTP = 40; bGMYC = 44;
The primary diagnostic feature of
Besides the elevated concentration of melanophores in the lateral line,
The DNA barcode data analysed recovered
We found that DNA barcodes were highly effective in highlighting and partitioning unrecognized diversity of lineages. This is especially the case within the genus
This study was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)/CT-Amazonia (575603/2008-9), Fundação de Amparo a Pesquisa do Estado do Amazonas (FAPEAM)/PRONEX, FAPEAM/SISBIOTA, and CNPq/SISBIOTA-BioPHAM (563348/2010) to IPF. We especially thank Marina Loeb (MZUSP) for helping with the holotype of
Ota RP, Machado VN, Andrade MC, Collins RA, Farias IP, Hrbek T. Integrative taxonomy reveals a new species of pacu (Characiformes: Serrasalmidae: Myloplus) from the Brazilian Amazon. Neotrop Ichthyol. 2020; 18(1):e190112. https://doi.org/10.1590/1982-0224-20190112
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