Knodus macrophthalmus (Román-Valencia, 2003)

Knodus macrophthalmus (Román-Valencia, 2003) (New combination)

Fig. 1 View FIGURE 1

Bryconamericus macrophthalmus Román-Valencia, 2003a: 7–15 View in CoL (original description; type locality: “ Venezuela, Amazonas State: Río Orinoco basin (sic), Río Negro, rapid above the mouth of Río Casiquiare, ca. 10 kilometers N of San Carlos de Río Negro (ca. 2°02'00"N, 67°25'00"W)”. Román-Valencia, 2005: 58–59, 64, fig. 11 (listed, photo of the holotype; diagnosis in key). Román-Valencia et al., 2008: 25 (diagnosis in key). Zarske et al., 2010: 9 (listed). Dagosta & Netto-Ferreira, 2015: 435, 440 (diagnosis from Bryconamericus pinnavittatus View in CoL ; listed in comparative material). Thomaz et al., 2015: Additional file 5, p. 9 (listed; generic assignment uncertain). DoNascimiento et al., 2017: 60 (listed, Amazon basin, Colombia; based on CZUT-IC 5124). Beltrão et al., 2019: Table S1 (listed; rio Negro basin); Dagosta & de Pinna, 2019: 74 (listed, “Negro, upper Orinoco”). Toledo-Piza et al., 2024: 120 (listed).

Knodus tiquiensis Ferreira & Lima, 2006: 630–639 View in CoL (original description; type locality: “ Brazil, Amazonas, Rio Tiquié, Indian village of Caruru, cachoeira do Caruru, 0°16'28.9"N, 69°54'53.6"W ”). Thomaz et al., 2015: Additional file 5, p. 8 (listed; probably a Knodus View in CoL s.s.). DoNascimiento et al., 2017: 59 (listed, Amazon basin, Colombia). Beltrão et al., 2019: Table S1 (listed; rio Negro basin). Bogotá-Gregory et al., 2022: 10 ( Colombia, Departamento Vaupés, Río Vaupés basin). Ferreira & Ohara, 2023: 374–375 (discussion on rheophyly; listed in comparative material). Melo et al., 2024: 7 (phylogenetic relationships; lot of voucher specimens LBP 6885, photos examined). Toledo-Piza et al., 2024: 214 (listed; mentioned as a possible synonym of Bryconamericus macrophthalmus View in CoL ). NEW SYNONYM.

Diagnosis. Knodus macrophthalmus is unique among its congeners by having the first six branched rays of the anal fin thicker and more expanded than the posterior rays. These thickened rays are associated with an interradial membrane that is significantly more developed and thicker than the membrane between the remaining anal-fin rays (see Ferreira & Lima, 2006 for more details). Knodus macrophthalmus can be diagnosed from all congeners, except K. deuterodonoides and K. nuptialis , by presenting relatively compressed dentary teeth, decreasing gradually in size along the dentary (vs. dentary teeth bulky, anteriormost four teeth considerably larger than remaining teeth; compare Ferreira & Lima, 2006: fig. 2A, and Menezes & Marinho: fig. 2, with Lima et al., 2003: fig. 2; Esguícero & Castro, 2014: fig. 2; de Sousa et al., 2020: fig. 2; Ferreira & Ohara, 2023: fig. 2). Knodus macrophthalmus can also be further distinguished from all congeners, except K. angustus , K. cismontanus , K. figueiredoi , K. geryi , K. meridae , K. nuptialis , K. obolus , K. rufford , and K. ytuanama , by having fewer branched anal-fin rays (14–16 vs. more than 17). Knodus macrophthalmus also differs from K. angustus , K. figueiredoi , and K. rufford by having heptacuspid teeth in the inner premaxillary series (vs. pentacuspid teeth in K. angustus and tricuspid teeth in K. figueiredoi and K. rufford ). It also differs from K. angustus by having four scale rows between the lateral line and the pelvic-fin origin (vs. three), and 14 circumpeduncular scales (vs. 11–12). It further differs from K. obolus by having a complete lateral line with 38–42 pored scales (vs. 35–37), and orbital diameter 30.8–41.1% of head length (vs. 41.3–46.3). Knodus macrophthalmus differs from K. cismontanus by having 38 vertebrae (vs. 33–34), and by having 38–42 pored scales on lateral line (vs. 32–38). Knodus macrophthalmus additionally differs from K. ytuanama by the presence of humeral blotches (vs. absence in adult specimens), and by presenting anteriormost anal-fin rays considerably longer and thicker than remaining rays, forming a conspicuous lobe (vs. anteriormost anal-fin rays only slightly longer than remaining rays, forming a discrete fin lobe). It is also distinguished from K. nuptialis by possessing a relatively broad midlateral stripe (vs. narrow), and by the absence of densely concentrated nuptial tubercles on the head, body, and fins, as well as the absence of a gill gland and bony hooks on the anal fin of mature males (vs. presence), and is additionally distinct from K. geryi by the absence of two symmetric, large dark blotches basally on caudal fin lobes (vs. presence). It is further distinguished from K. deuterodonoides by having 14–16 branched anal-fin rays (vs. 17–18).

Remarks. The examination of the holotype and part of the paratypes of Bryconamericus macrophthalmus by the first author, as well as the direct comparison of two paratypes (MZUSP 99141; formerly MBUCV 11381) with the holotype and most of the type series of Knodus tiquiensis , revealed that both nominal species refers to a single taxon. There are no differences in morphometric or meristic features between the type-series of both nominal species (see Table 1). Moreover, the type-series of Bryconamericus macrophthalmus presents all diagnostic features present in Knodus tiquiensis . Although the original description of Bryconamericus macrophthalmus does not list any of the diagnostic features proposed by Ferreira & Lima (2006) for K. tiquiensis , the examination of its type material showed that all of them are present in the species. We consequently consider Knodus tiquiensis as a junior synonym of Bryconamericus macrophthalmus , under the new combination, Knodus macrophthalmus .

It is important to remark that none of the features listed in the original diagnosis of Knodus macrophthalmus by Román-Valencia (2003a: 9) are actually diagnostic for the species. For example, he states that the premaxillary teeth are arranged with tricuspid teeth alternating with “multicuspid teeth”. Since he described the outer premaxillary teeth to be tricuspid and the inner premaxillary teeth as pentacuspid (although the correct number is seven cusps) in the description (p. 10), the condition he is actually describing for Knodus macrophthalmus is not unique but rather quite widespread not only among congeners, but in stevardiids in general. Another purported diagnostic feature, the presence of a third unicuspid tooth in the maxilla, is probably an artefact resulting from the third teeth in the specimen depicted by Román-Valencia (2003a: 8, fig. 3) to be broken, as all examined specimens examined herein and in Ferreira & Lima (2006) exhibited the maxilla bearing two or three pentacuspid teeth. The number of vertebrae (39) is both more variable as the actual range is 38–39, as well as overlapped by many congeners, as K. figueiredoi , K. geryi , and K. tanaothoros ( Esguícero & Castro, 2014; Lima et al., 2004; Weitzman et al., 2005).

Subsequently, Román-Valencia (2005: 64) and Román-Valencia et al. (2008: 25) suggested that the species could be diagnosed from most congeners in the genus Bryconamericus occurring in Ecuador and Venezuela by presenting more than 40 scales in the lateral line, when actually lateral line scale counts in the species ranges from 38 to 42 scales, modally 39 ( Ferreira & Lima, 2006; see also Table 1).

DoNascimiento et al. (2019: 60) listed Bryconamericus macrophthalmus for the Amazon basin in Colombia. This record is based on the lot CZUT-IC 5124 , collected at the Río Aquío , a tributary of the Río Guainía / Río Negro , Departamento Guaínia. We unfortunately were unable to check this lot but this locality is not far from the type locality of the species and as such within its expected range .

Román-Valencia (2003a: 8) cited the type-locality of Bryconamericus macrophthalmus as being “above the mouth of Río Casiquiare”. However, the label of the holotype and paratypes actually state that the type locality is below (“abajo”) the mouth of the Río Casiquiare. There is a small rapid approximately 10 km north of San Carlos de Río Negro (distance estimated on Google Earth using the rule tool) that with all likelihood corresponds to the type locality of Bryconamericus macrophthalmus . We thus propose herein to amend the type locality of the species to: “ Venezuela, Amazonas state, Río Negro, rapid below the mouth of Río Casiquiare, ca. 10 km north of San Carlos de Río Negro, c. 1º59'0"N, 67º7'30"W ”.

Distribution. Knodus macrophthalmus is known from the upper rio Negro basin, including the rio Uaupés/ Vaupés basin, Amazon basin, in Brazil, Colombia, and Venezuela ( Fig. 1 View FIGURE 1 ). Román-Valencia (2003a: 8) inadvertently mentioned “Río Orinoco basin” when stating the type locality of the species, even though it lies at the rio Negro main stem. Presumably influenced by that mistake, Dagosta & de Pinna (2019: 74) cited the species as occurring at the “upper Orinoco”, even though there are no confirmed records so far for the species from that river basin.

Material examined: Brazil: ZUEC 16101 View Materials (33, 15.4–44.7 mm SL): Amazonas, São Gabriel da Cachoeira, rio Negro , opposite Ilha da Adama , 0º8'13"S, 67º4'58"W; F.C GoogleMaps . T. Lima, G. C. Bortolo & T.C. Faria , 18–22 Feb 2018 . Colombia: CZUT-IC 12307 (30, 17.9–50.2 mm SL): Vaupés, río Vaupés, Cachivera Vacuraba , 1º12'4"N, 70º1'59"W; F. Villa, 9 Nov 2009 GoogleMaps . CIACOL 1003 (1, 45.3 mm SL), Vaupés, río Paca (trib. río Vaupés), Cachivera Muela, Acariquara village , 0º42'47"N, 70º15'37"W; J. Dámaso, 22 Nov 2012 GoogleMaps . Venezuela: MBUCV 29392 View Materials (1, 39.0 mm SL), holotype, Estado Amazonas, Río Negro, raudal, below the mouth of Río Casiquiare , approx. 10 km N of San Carlos de Río Negro, c. 1º59'0"N, 67º7'30"W; K. Clark, 26 Jun 1978 GoogleMaps . MBUCV 11381 View Materials (10, 21.9–47.5 mm SL) ; MZUSP 99141 View Materials (ex MBUCV 11381 View Materials ) (2, 36.1–46.9 mm SL), paratypes, same data as holotype GoogleMaps .