Tetragonopterus anostomus Silva & Benine, 2011

Silva, Gabriel S. C., Melo, Bruno F., Oliveira, Claudio & Benine, Ricardo C., 2016, Revision of the South American genus Tetragonopterus Cuvier, 1816 (Teleostei: Characidae) with description of four new species, Zootaxa 4200 (1), pp. 1-46 : 27-29

Tetragonopterus anostomus Silva & Benine, 2011

Fig. 8

Tetragonopterus anostomus Silva & Benine, 2011: 50 –56 (original description; type locality: “Goiás state, Nova Crixás, rio Preto, rio Araguaia basin; Silva et al., 2013: 1613 –1631 (diagnosis); Araujo & Lucinda, 2014: 309 –315 (diagnosis). Tetragonopterus akamai Araujo & Lucinda, 2014: 309 –315. (original description; type locality: “Tocantins, Peixe, rio Tocantins close to the confluence with rio Santa Tereza).

Diagnosis. Tetragonopterus anostomus is distinguished from all congeners by having subsuperior mouth (vs. terminal mouth). Tetragonopterus anostomus differs from all other species, except T. araguaiensis , by the presence of 17–19 gill rakers on the lower limb of the first gill arch (vs. 11–14). It differs from its congeners, except T. denticulatus , T. juruena and T. kuluene by bearing 5–6 principal teeth on dentary (vs. 4) and by having thinner and sharper teeth on dentary (vs. large and more robust teeth). Tetragonopterus anostomus further differs from T. ommatus by the presence of 2–4 teeth on maxilla (vs. 7–8) and by having a mark centered on the caudal peduncle (vs. mark limited to the posterior portion of the peduncle). Tetragonopterus anostomus differs from T. carvalhoi by the presence of a rounded mark on the caudal peduncle (vs. a lozenge-shaped mark). It differs from T. rarus by the absence of longitudinal dark stripes on the flank (vs. the presence of stripes). Tetragonopterus anostomus differs from T. rarus and T. georgiae by having 3.5 longitudinal scale rows between lateral line and pelvic-fin origin (vs. 4.5–5.5). Finally, T. anostomus differs from T. argenteus by possessing eight predorsal scales (vs. 11–17).

Description. A detailed description of Tetragonopterus anostomus was recently provided by Silva & Benine (2011).

Distribution. Tetragonopterus anostomus was described from the rio Araguaia system. During the course of this study, several specimens of T. anostomus were also found in the Rio Tocantins, which is not surprising given the fact that the rio Araguaia is a tributary of the rio Tocantins ( Fig. 2 a).

Remarks. Araujo & Lucinda (2014) recently described Tetragonopterus akamai based on material collected in the Rio Tocantins basin. This species has a strong resemblance with T. anostomus from the Tocantins-Araguaia system. A reanalysis of type specimens of T. akamai provided evidence that T. akamai is a junior synonym of T. anostomus ( Fig. 9 ). The main character used to diagnose T. akamai from T. anostomus and from all others congeners is the shape of the anterodorsal portion of the maxilla, which is bent over and in close contact with the dorsal suface of the premaxilla (vs. anterodorsal portion of the maxilla not bent over and not in contact with the dorsal surface of the premaxilla, according to Araujo & Lucinda, 2014). The examination of a cleared and stained paratype (UNT 2788) and non-type specimens (MZUSP 52120) of T. akamai revealed that the anterodorsal portion of the maxilla is not bent over the premaxilla as stated in the original description ( Araujo & Lucinda, 2014: fig. 2). The anterodorsal tip of the maxilla of a paratype of T. anostomus (LBP 7687; Fig. 9 c) is even more bent downward than that observed in the paratype of T. akamai (UNT 2788; Fig. 9 a). Further, we noticed substantial variability in the shape of the anterodorsal portion of the maxilla in specimens of T. argenteus . The summed evidence above clearly indicate that this character used to diagnose T. akamai is extremely variable within Tetragonopterus and should not be regarded as a valid character for diagnosing taxa at the specific level. Other proposed characters to diagnose T. akamai from T. anostomus are snout length and size of teeth in the inner series of premaxilla ( Araujo & Lucinda, 2014). However, we have not observed significant differences in these two features that allowed the distinction of two species. In order to further evaluate the hypothesis of conspecificity between these two nominal taxa, we included specimens of T. akamai from a locality where paratypes of this nominal species were collected (Brejinho de Nazaré, Rio Tocantins; see Table 1) and used a molecular approach to evaluate the genetic divergence between both nominal taxa. Our results show no genetic divergence (genetic distance = 0.0%) between these samples ( Fig. 1 ), which means that T. akamai from the Rio Tocantins has the same genetic information (COI sequences) as T. anostomus from the Rio Araguaia. Thereby, both morphological and molecular evidence support that T. akamai as a junior synonym of T. anostomus .

Material examined. Types: Tetragonopterus anostomus : MZUSP 108957 , holotype, 45.4 mm SL, Goiás, Nova Crixás , Araguaia basin, Rio Preto , 14°22’18”S 50°39’13”W, L. S. Sousa, M. Melo, C. Chamon and L. M. Sousa, 26 Jul 2005 . MZUSP 89295, 5 paratypes, 34.8–41.0 mm SL, collected with holotype. LBP 7687, 17 paratypes (2 c&s), 34.6–38.9 mm SL, Mato Grosso, Cocalinho, marginal lagoon of the Rio Araguaia. Tetragonopterus akamai : UNT 2800, 2 , 50.5– 49.9 mm SL, Tocantins, Peixe , Tocantins basin, Lagoa Água Branca , 11°49’20”S 48°38’40”W, 13 Oct 2000 . UNT 5176, 5 , 49.6–54.3 mm SL, Tocantins, Brejinho de Nazaré, Tocantins basin, Lagoa Capivara , 11°12’9”S 48°30’14”W, 14 Feb 1996 . UNT 5175, 3 , 34.1–35.6 mm SL, Tocantins, Ipueiras , Rio Tocantins basin, 11°18’55”S 48°27’28”W, L. Araujo & P. Lucinda, 28 Nov 2001 . UNT 2788, 1 c&s, 54.4 mm SL, Tocantins, Brejinho de Nazaré, Tocantins basin, Lagoa Capivara , 11°12’9”S 48°30’14”W, L. Araujo & P. Lucinda, 14 Feb 1995 . Non types. LBP 19055, 6, 36.9–42.8 mm SL, Tocantins, Brejinho de Nazaré, Tocantins basin, Rio Crixás , 11°03’14.3”S 48°34’22.0”W . MZUSP 18106, 1 , 63.9 mm SL, Pará, Tocantins basin, Igarapé Muru . MZUSP 52120, 18 (2 c&s), 44.2–55.8 mm SL, Tocantins, Araguaçu, Araguaia basin, Rio Água Fria , 12°44’42”S, 49°56’11”W . MZUSP 89096, 2 , 44.3– 35.8 mm SL, Goiás, Aruanã, Araguaia basin, 14°45’50”S 050°57’50”W . MZUSP 89190, 1 , 38.6 mm SL, Goiás, Aruanã, Araguaia basin, Rio do Peixe , 14°20’11”S 50°46’31”W . MZUSP 89446, 4 , 30.3–41.1 mm SL, Goiás, Nova Crixás, Araguaia basin, 13°46’28”S 50°16’00”W . NUP 12746, 4, 47.6–52.6 mm SL, Mato Grosso, Cocalinho, Araguaia basin, Lago Montaria , 13°22’43”S 50°40’15”W . NUP 12922, 2, 61.7–62.4 mm SL, Goiás, São Miguel do Araguaia, Araguaia basin, Lago Piratinga , 13°04’10.5”S 50°35’06.7”W.

Figures

FIGURE 1. Maximum likelihood tree of Tetragonopterus based on partial sequences of cytochrome oxidase c subunit I. Black circles represent bootstrap support ± 80 %; grey circles represent bootstrap support between 50 % and 79 %; values <50 % are not shown. Voucher numbers are represented after species names.

FIGURE 8. Tetragonopterus anostomus. a) MZUSP 108957, holotype, 45.4 mm SL, Brazil, Mato Grosso, Nova Crixás, Rio Preto, Rio Araguaia. b) LBP 19055, 42.8 mm SL, Brazil, Tocantins, Brejinho de Nazaré, Rio Crixás, Rio Tocantins. Photo (a) from Silva & Benine (2011) and (b) by M. Taylor.

FIGURE 9. Lateral view of the maxilla and premaxilla: a) Tetragonopterus akamai, UNT 2788, paratype, 54.4 mm SL, Rio Tocantins; b) T. anostomus, MZUSP 52120, non-type, 44.2 mm SL, Rio Tocantins; c) T. anostomus, LBP 7687, paratype, 32.5 mm SL, Rio Araguaia. Scale bar = 10 mm.