Taxonomic revision of modern Doras Lacepède, 1803 (Siluriformes: Doradidae), with descriptions of three new species



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Mato Grosso: ANSP 181056 (5 alc. 57.6–63 mm; 1 cs, 58 mm), Rio Corisevo, Porto do Vitório, near Ribeirão Kevuaieli, 13°02’05”S, 053°25’10”W (AXE2004101904), C. Moreira et al., 19 Oct 2004; MZUSP 86887 (5 alc, 56.4–64.7 mm), Rio Sete de Setembro, approx. 20 km west of Canarana by road MT-020 (Canarana-garapu), 13°30’19”S, 052°24’57”W, C. Moreira, et al. 19 Oct 2004; MZUSP 87025 (17 alc, 59.6–75 mm), same data as ANSP 181056; MZUSP 87055 (2 alc, 69.6–70.5 mm), Rio Corisevo, rockbed and beach under bridge of road to Sorriso, approx. 30 km west of Gaúcha do Norte, 13°12’58”S, 053°29’53”W (AXE2004101906), C. Moreira et al., 19 Oct 2004; Pará: ANSP 181057 (1 alc, 160 mm), Rio Xingu, Belo Monte, 03°07’S, 051°42’W (MIG83070002), M. Goulding, Jul 1983; ANSP 187378 (1 alc), same data as holotype; INPA 4051 (6 alc, 168–213.5 mm), Rio Xingu, Altamira, L. Rapp Py-Daniel & J.A. Zuanon, 1 Oct 1990; INPA 4052 (7 alc, 153–240 mm), Rio Xingu, Ilha do Babaquara, Altamira, L. Rapp Py-Daniel & J.A. Zuanon, 5 Oct 1990; MNHN 1999-0020 (1 alc, 206 mm), Rio Xingu (lower), Cachoeira Kaituka, M. Jégu, 10 Oct 1992; MZUSP 82297 (3 alc, 164.6–183.8 mm), same data as ANSP 181057; MZUSP 96334 (1 sk), same data as holotype.

Non-type material.—Brazil: Para (Jari Dr.): INPA 5250 (12 alc, 65.7-201 mm), Rio Jari, north-northeast of Almeirim, approx. 00°52’S, 052°25’W (MJ87062314), M. Jégu & J.A. Zuanon, 23-24 Jun 1987; (Trombetas Dr.): Oriximinã Municipality: ANSP 187380 (1 alc, 202 mm), Rio Trombetas, Igarapé Caxipacoré, E.G. Ferreira et al., 20 Apr 1985; INPA 3548 (1 alc, 202 mm) Rio Trombetas, upstream of Vira Mundo (waterfall) 01°45’S, 055°52’W (EGF85100821), E.G. Ferreira & L. Rapp Py-Daniel, 8 Oct 1985; INPA 5065 (2, 190–197 mm), Rio Trombetas, Cachoeira Porteira, E.G. Ferreira & M. Jégu, 15 Apr 1985; INPA 5068 (2 alc, 153.5–217 mm) Rio Cachorro, E.G. Ferreira, 26 May 1988; INPA 5447 (5 alc), same data as ANSP 187380; INPA 5568 (5 alc, 60.9–132 mm); Rio Trombetas, upstream of Cachoeira Vira-Mundo, E.G. Ferreira & J.A. Zuanon, 3 Sep 1990.
Diagnosis.—Doras higuchii is diagnosed among fossil and modern congeners by the following combination of characteristics. Midlateral scutes 33–36; gas bladder with single terminal diverticulum (Figs. 6C–D); teeth typically present on premaxillae; infraorbital one with elongate anterior wing extending well beyond mesial concavity for anterior nare; ventral surface without conspicuous pores or with few small pores restricted to skin around vent (Fig. 3A); symphyseal limbs of cleithrum with concave lateral and anteriormost margins; distal anterior margin of pectoral spines smooth; postinfranuchal midlateral scutes overlapping and of more or less uniform depth anterior to anal fin; infranuchal scute with medial thorn flanked by subtriangular wings; postcleithral process always deep (depth 1.8–2.49 times into oblique length) with straight to weakly convex free dorsal margin and dorsal field ornamentation broadly expanded, forming one-third to half of posterior margin of process (Fig. 2E); skin covering dorsal-locking spine and sometimes base of dorsal spine blackened with strong concentration of melanophores, distal dorsal spine markedly depigmented, pale (Fig. 11); caudal fin with greater concentration of melanophores on lower rays and membranes of upper lobe and upper rays and membranes of lower lobe forming two dusky stripes, particularly in juveniles (Fig. 11E).

Comparisons.— Doras phlyzakion and D. zuanoni have 30–32 midlateral scutes, gas bladder with two posterior diverticula (Figs. 6G–H), premaxillae edentate, infraorbital one relatively short, anterior tip extended short distance beyond mesial concavity for anterior nare (Fig. 4A), ventral surface with many small pores in skin particularly on abdomen and near ventral insertion of gill flap (Figs. 3B–C); symphyseal limbs of cleithrum with straight lateral margins and rounded, convex anteriormost margin; and distal anterior margin of pectoral spines serrated. Doras micropoeus has postinfranuchal midlateral scutes distinctly increasing in separation and decreasing in depth anteriorly from above anal-fin origin; infranuchal scute lacking posteriorly pointed wings and with medial thorn absent or rudimentary (Fig. 5C). Doras carinatus has postcleithral process deep to shallow (depth 2.28–3.93 times into oblique length) with straight to weakly concave free dorsal margin and dorsal field ornamentation moderately expanded, excluded from or forming less than one-third of posterior margin of process (Figs. 2B–D); skin covering dorsal-locking spine and base of dorsal spine moderately darkened by weak concentration of melanophores with dorsal spine dusky or becoming gradually lighter distally (Figs. 8, 9); caudal fin uniformly dusky with scattered melanophores (Figs. 8, 9). †Doras dioneae has a shallower postcleithral process (depth 2.75 times into oblique length) with free dorsal margin weakly concave and dorsal field ornamentation moderately expanded, forming minimal portion of posterior margin (Fig. 2A). Doras higuchii is further distinguished from †Doras dioneae by sharing the same combination of characteristics of the pectoral girdle described for D. carinatus (see Diagnosis of D. carinatus).

Description.—Morphometrics and meristics summarized in Table 4; aspects of postcleithral process summarized in Table 1. Largest specimen examined 240 mm SL (INPA 4052). Body elongate, slightly compressed, deepest at dorsal-fin origin, gently tapering to short, slender caudal peduncle. Ventral surface flattened from snout to anal-fin origin. Head large, deep, weakly compressed with prominent conical snout; dorsal profile straight to concave from snout tip to between anterior and posterior nares, then either curving gently (convex) to above eye and finishing straight, weakly oblique to dorsal-fin origin or curving more continuously (shallowly convex) from posterior nare to dorsal-fin origin. Eyes large (21.91–30.99% of head length), covered by thin skin (adipose eyelid not distinct), positioned high on the head; dorsal margin of orbit strongly concave; interorbital width narrow to moderate (13.89–22.92% of head length).

Mouth small, subterminal; gape with rounded (concave) anterior (premaxillary) margin, straight to weakly concave posterior (dentary) margin. Teeth present on dentaries and typically premaxillae. Each premaxillae usually with 2–5 strong acicular teeth set close in one or two irregular rows (n = 7, SL 153–240 mm); rarely edentate. Each dentary with 14–22 strong acicular teeth in a few rows or small patch.

Anterior and posterior nares separate, surrounded by short tubular skin; posterior nare larger than anterior, located more or less at midpoint between anterior nare and anterior margin of eye; anterior nare closer to posterior nare than snout tip. Cephalic shield weakly ornamented, often with middorsal furrow from middle pitline of supraoccipital usually to suture between anterior and middle nuchal plates, sometimes extending onto middle nuchal plate. Cranial fontanel with single opening anterior to epiphyseal bar (portion posterior to epiphyseal bar occluded). Fontanel elongate, narrow, widest posteriorly with rounded margin, attenuate anteriorly; enclosed posteriorly and laterally by frontals, anteriorly by mesethmoid (compare Fig. 1B). Nuchal foramina absent. Nuchal shield roof-shaped, forming transverse angle. Anterior nuchal plate well-developed, subpentagonal to subhexagonal, wider than long and sharing broad lateral suture with epioccipital. Mesethmoid elongate, attenuate anteriorly with pointed tip. Infraorbital one (lacrimal) elongate with long tapered anterior wing extending well beyond mesial concavity for anterior nare (most similar to D. carinatus).

Three pairs of barbels: maxillary, inner and outer mental. Maxillary barbel long, tip more or less reaching medialmost point of gill opening; fimbriate with 15-18 fimbriae along lateral margin, proximal fimbriae with secondary fimbriae along trailing margin. Mental barbels nearly equal in size, finishing about halfway between anterior margin of lower jaw and medialmost point of gill opening, bases thick, profusely ornamented with fleshy papillae. Lips fleshy, surfaces with low rounded papillae near insertion of maxillary barbels.

Pectoral girdle in ventral view subtriangular, similar in shape to D. carinatus with lateral and anteriormost margins of symphyseal limbs of cleithrum concave. Transverse limb of coracoid process with distinct posterior process (keel) relatively short as in other Doras. Ventral surfaces of pectoral girdle (including posterior processes of coracoid) covered with skin (not exposed).

Postcleithral process blade-like, deeply subrectangular in adults; depth greatest in Xingu specimens (1.8–2.38 times into oblique length), less so in Trombetas specimens (2.4–2.49 times into oblique length). Margins entire; free dorsal margin of process straight or more often weakly convex. Surface ornamentation similar to D. carinatus except dorsal field more broadly expanded, forming one third to half of posterior margin of process, and region near distal border between dorsal and middle fields often covered with short sliver of pigmented skin (Fig. 2E).

Skin relatively smooth except for extremely minute punctate tubercles. In Trombetas specimens tubercles densely scattered or in irregular rows on upper sides, particularly in tympanic region. In Xingu specimens tubercles sparsely scattered on head, body and fins, particularly on gill covers and dorsal surfaces of head; specimens also with tubercles crowded in wide patch below infranuchal scute along posterior margin of postcleithral process, extending ventrally to lowermost sides. Elongate slit-like pore in axillary of pectoral fin. Skin beneath entire length of postcleithral process perforated with numerous small round pores imparting a sponge-like appearance (Fig. 2E). Numerous pores crowded in skin surrounding vent (Fig. 3A); pores absent from belly and breast.

Dorsal fin I,6 (n = 32); pectoral fin modally I,9, range I,8–10 (32); pelvic fin i,6 (32), anal fin modally v,9, range iv–vi,8–10 (12), caudal fin typically i,7/8,i (31), rarely i,7/7,i (1) with dorsal procurrent rays modally 13, range 12–14 (22) and ventral procurrent rays modally 14, range 12–14 (22). Dorsal-fin origin located more or less two-fifths SL from snout tip. Morphology of fins as largely as described for D. carinatus except caudal-fin more deeply forked, lobes bluntly pointed.

Lateral line ossified with complete series of 33–36 midlateral scutes per side (modally 34; n = 32). Scute morphology as described for D. carinatus.

Gas bladder large, cordiform with paired posterior chambers longer than single anterior chamber; walls smooth except for single terminal diverticulum most similar to D. carinatus (Figs. 6C–D).



Coloration.—Preserved specimens with dorsal and dorsolateral surfaces of head and body uniform gray to tan ground color; sides of body below medial thorns lighter gray or tan to pale, relatively depigmented with few melanophores; lowermost sides and ventral surfaces pale, white. Maxillary barbel gray to tan; mental barbels pale. Skin covering base of dorsal-locking and dorsal spines blackened with strong concentration of melanophores; distal portion of dorsal spine usually markedly depigmented, pale; melanophores scattered on rays and membranes along anterior margins of rays, remaining portions of membranes clear. Pectoral fins dusky with scattered melanophores particularly on spine and anteriormost rays and membranes. Pelvic fins similarly dusky with scattered melanophores, particularly on anterior membranes. Anal fin largely pale with few scattered melanophores. Caudal fin with melanophores concentrated on lower rays and membranes of upper lobe and upper rays and membranes of lower lobe, forming two dusky stripes (particularly evident in juveniles, Fig. 11A). In life dorsal head and sides above midlateral plates tinted olive green; scutes and portions of snout and fins tinted yellowish-green; lower sides and undersurfaces white (Fig. 11C).

Distribution and habitat.—Doras higuchii occurs in the lower Jari, lower Trombetas and Xingu basins, all tributary to the lower Amazon, in the States of Mato Grosso and Pará, Brazil. Three adults taken at the type locality in the Rio Curuá were collected over sand in swift clear water (depth <2 m) immediately below a large cataract.

Etymology.—Species named in honor of Horácio Higuchi in recognition of his groundbreaking contributions to the systematics of the thorny catfishes.
Doras phlyzakion, new species

Figs. 2G, 3C, 4A, 6G, 7 & 12A; Tables 1 & 5


Holotype.—Brazil: Amazonas: MZUSP 88508 (alc, 160.8 mm), Rio Tefé (Amazonas Dr.), beach, Vista Escura, 03°38’S, 064°59’W (MIG1979073001), M. Goulding, 30 Jul 1979.

Paratypes.—Brazil: Amazonas (Negro Dr.): MZUSP 91671 (1 alc, 87.5 mm), Rio Uaupés, 00°09’N, 067°50’W, J.Chernela, no date; MZUSP 50836 (1 cs, 87.3 mm), Lagoa Central, lower Rio Negro basin between Rios Camanaú and Apuaú, approx. 100-180 km NW of Manaus (TYR68112001), T.R. Roberts, 20 Nov 1968; (Solimões-Amazon Dr.): ANSP 181055 (2 alc, 148–169 mm), same data as holotype; INPA 19140 (4 alc, 86.4-136.8 mm), Lago Amanã, mouth of Rio Baré, 02°23’S, 064°42’W, W. Crampton, 13-18 Dec 1997; INPA 19141 (1 alc, 76.8 mm), Rio Tefé, Ilha do Martelo, 03°38’S, 064°59'W, W. Crampton, 16 Sep 1999; MCP 32947 (1 alc, 175 mm), Lago Amanã, mouth of Rio Baré, 02°27’23”S, 064°43’35”W (WC1997121301), W. Crampton, 13 Dec 1997; MCP 32948 (1 alc, 73.2 mm), Lago Tefé, community of Nogueira, 03°17’58”S 064°46’21”W (WC1997101301), W. Crampton, 13 Oct 1997; MCP 32949 (5 alc, 90.7–113.8 mm), Lago Amanã, mouth of Rio Baré, 02°27’S, 064°43’W (WC1997121801), W. Crampton, 18 Dec 1997; MCP 32950 (1 alc, 145.3 mm), Lago Tefé, community of Nogueira 03°17’58”S 064°46’21”W (WC1997101401), W. Crampton, 14 Oct 1997; MHNG 2699.05 (1 alc), same data as holotype; MZUSP 50837 (4 alc, 98.6–133.3 mm), Rio Solimões, Fonte Boa, 02°31’S, 066°06’W (EPA68102502) Expedição Permanente à Amazônia, 25 Oct 1968; MZUSP 82294 15 1 0 145.5–189.3 alc, 165 sk), same data as holotype; MZUSP 88466 (6 alc, 159–167.2 mm), Rio Tefé [label indicates "Mucura", presumably in error], M. Goulding, 30 Jul 1979; Roraima (Negro Dr.): MZUSP 62583 (1 alc, 116.6 mm), Rio Mucajaí, trib Rio Branco, south of Boa Vista, 02°32’N, 060°54’W, E. Dente, Apr 1962; Colombia (Japurá Dr.): Vaupés: IAvH-P 2860 (1 alc), Laguna Taraira, Río Apaporis, northeast of La Pedrera, H. Lopez, 13 Jun 1990.
Diagnosis.—Doras phlyzakion is diagnosed among modern congeners by a single unique characteristic: gas bladder with two elongate posterior (subterminal) diverticula with bases well separated (Fig. 6G). Doras phlyzakion is distinguished from fossil species †Doras dioneae by having a shallow postcleithral process, depth 3.05–3.84 (vs. 2.75) times into oblique length. Additional characteristics diagnostic in combination include: midlateral scutes 31–32; premaxillae edentate; infraorbital one (lacrimal) relatively short, anterior tip extended short distance beyond mesial concavity for anterior nare (Fig. 4A); ventral surface with numerous pores in skin on breast (Fig. 3C); symphyseal limbs of cleithrum with straight lateral margins and rounded, convex anteriormost margin; distal anterior margin of pectoral spines serrated; midlateral scutes 31–32; infranuchal scute with distinct medial thorn and posteriorly pointed dorsal and ventral wings; postinfranuchal scutes uniform in size and overlapping anteriorly from above anal fin; middorsum and sides dusky, weakly contrasting pale midlateral stripe along scutes; fins without distinct dark marks; and interorbital width 17.07–24.03% of head length.

Comparisons.—Doras carinatus, D. higuchii and D. micropoeus have gas bladder with single terminal diverticulum (Figs. 6A–F); premaxillae with acicular teeth; infraorbital one elongate, anterior wing well-developed with tip extending well beyond anterior nare (Figs. 4B–D); ventral surface with pores absent or restricted to skin surrounding vent (Fig. 3A); symphyseal limbs of cleithrum with concave lateral and anteriormost margins; and distal anterior margin of pectoral spines smooth. Doras carinatus and D. higuchii are further distinguished by having more midlateral scutes, 33–36. Doras micropoeus is further distinguished by having infranuchal scute with medial thorn absent or rudimentary and posteriorly pointed wings lacking (Fig. 5C); and postinfranuchal scutes non-overlapping and decreasing in size or absent anteriorly. Doras zuanoni is distinguished by having two terminal diverticula cojoined at base with long divergent ends and short diverticulum present on each anterior lateral shoulder of anterior chamber (Fig. 6H); pores on breast few, restricted to small patch near ventral medial insertion of gill flap (Fig. 3B); sides dusky to black, strongly contrasting pale midlateral stripe (Figs. 12B–C); fins with dark marks; and interorbital width 26.7–28.24% of head length.

Description.—Morphometrics and meristics summarized in Table 5; aspects of postcleithral process summarized in Table 1. Largest specimen examined 189.3 mm SL (MZUSP 82294). Body elongate, slightly compressed, deepest at dorsal-fin origin, gently tapering to short, slender caudal peduncle. Ventral surface flattened from snout to anal-fin origin. Head large, deep, weakly compressed with prominent conical snout; dorsal profile straight to weakly concave from snout tip to between anterior and posterior nares, then curving gently (convex) to above eye, continuing straight, weakly oblique to middle pitline of supraoccipital and finishing with low rounded (convex) hump along nuchal shield. Eyes very large, covered by thin skin (adipose eyelid not distinct), positioned high on the head; dorsal margin of orbit strongly concave; interorbital width narrow to moderate (17.07–24.03% of head length).

Mouth small, subterminal; gape with rounded (concave) anterior (premaxillary) margin, straight to weakly concave posterior (dentary) margin. Teeth absent from premaxillae. Each dentary typically with 4–15 acicular teeth in small patch.

Anterior and posterior nares separate, surrounded by short tubular skin; posterior nare larger than anterior, located more or less at midpoint between anterior nare and anterior margin of eye; anterior nare closer to posterior nare than snout tip. Cephalic shield weakly ornamented, typically without distinct middorsal furrow posterior to middle pitline of supraoccipital. Cranial fontanel with single opening anterior to epiphyseal bar (portion posterior to epiphyseal bar occluded). Fontanel elongate, narrow, widest posteriorly with rounded margin, attenuate anteriorly; enclosed posteriorly and laterally by frontals, anteriorly by mesethmoid, and set in shallow bony furrow that continues posteriorly onto supraoccipital, finishing before middle pitline. Nuchal foramina absent. Nuchal portion of cephalic shield slightly elevated forming low rounded hump and roof-shaped, forming transverse angle. Anterior nuchal plate well-developed, subpentagonal to subhexagonal, wider than long and sharing broad lateral suture with epioccipital. Mesethmoid elongate, anterior end attenuate with pointed tip. Infraorbital one (lacrimal) comparatively short, anterior end evenly tapered and extending relatively short distance beyond mesial concavity for anterior nare (Fig. 4A). Epioccipital posterior process long, ribbon-like, twisted from horizontal plane (anteriorly) to vertical plane (posteriorly), not expanded posteriorly, and weakly contacting posterior nuchal plate.

Three pairs of barbels: maxillary, inner and outer mental. Maxillary barbel long, tip finishing more or less at medialmost point of gill opening; fimbriate with 6-10 fimbriae along lateral margin; proximal fimbriae rugose with elongate papillae. Mental barbels nearly equal in size, finishing about halfway between anterior margin of lower jaw and medialmost point of gill opening; bases thick, profusely ornamented with fleshy papillae. Lips fleshy, surfaces with low rounded papillae near insertion of maxillary barbels.

Pectoral girdle in ventral view subtriangular; elongated anteriorly with convergent lateral margins of paired symphyseal (horizontal) limbs of cleithrum long, straight. Anteriormost margin of pectoral girdle bluntly rounded (convex). Transverse limb of coracoid with distinct posterior process (keel) relatively short, extending slightly beyond posterior insertion of pectoral fin. Distal ends of posterior coracoid processes with weak ornamentation (ridges) visible beneath thin skin. Remaining ventral surfaces of pectoral girdle covered with slightly thicker skin.

Postcleithral process blade-like, long and shallowly subrectangular (depth 3.05–3.84 times into oblique length in adults); margins entire, without conspicuous dentations. Dorsal margin variable, usually lacking distinct hump below posterior margin of supracleithrum; dorsal free margin either straight, forming distinct dorsal posterior corner with oblique posterior margin (Fig. 2G), or weakly convex, curving continuously to ventral posterior corner. Ventral margin nearly straight from shoulder to ventral posterior corner of process. Lateral surface of postcleithral process with three longitudial fields of ornamentation usually evident, as described for D. carinatus except middle field longer and narrower.

Skin relatively smooth except for extremely minute punctate tubercles scattered on head, body and fins, particularly on skin in tympanal region above postcleithral process. Elongate slit-like pore in axillary of pectoral fin. Skin beneath entire length of postcleithral process perforated with numerous small round pores imparting a sponge-like appearance. Smaller pores present in skin above and below anterior midlateral scutes. Ventral surfaces (including branchiostegal membranes) with many conspicuous pores, particularly in skin covering breast and abdomen and surrounding vent (Fig. 3C).

Dorsal fin I,6 (n = 34); pectoral fin modally I,9, range I,8–10 (34); pelvic fin i,6 (34), anal fin modally v,9, range iv–v,9–10 (12); caudal fin i,7/8,i (35) with dorsal procurrent rays modally 14, range 12–15 (34) and ventral procurrent rays modally 13, range 12–15 (34). Dorsal-fin origin located more or less two-fifths SL from snout tip. Morphology of fins as described for D. carinatus except pectoral-fin spines with teeth along entire anterior margin and caudal-fin lobes slightly more elongate with rounded points.

Lateral line ossified with a complete series of 31–32 scutes per side (modally 32; n = 34). Morphology largely as described for D. carinatus except midlateral scutes with posterior margins weakly serrate, and depth of midlateral scutes slightly greater, nearly one-third corresponding body depth at pelvic-fin origin.

Gas bladder large, cordiform with paired posterior chambers longer than single anterior chamber (Fig. 6G). Each posterior chamber with a relatively long, finger-like posterior (subterminal) diverticulum with bases well separated.



Coloration.—Coloration in alcohol largely as described for D. carinatus except midlateral scutes more depigmented making pale midlateral stripe more conspicuous, pelvic fins more depigmented with fewer melanophores on dorsal surface, and anal fin clear, without melanophores.

Distribution and habitat.—Doras phlyzakion is known from lowland drainages in the Solimões (Apaporis, Tefé, Lago Amaña) and Negro (Uaupés, Branco) basins in Brazil and Colombia. This species is apparently prefers lentic habitats as it is often recorded from large permanent lakes on the floodplains of major rivers.

Etymology.—Species name from the Greek phlyzakion, meaning blister (Jaeger, 1950), alluding to the abundant pores on the ventral surface of body. A noun in apposition.
Doras zuanoni, new species

Figs. 2H, 3B, 6H, 7 & 12B–C; Tables 1 & 6


Holotype.—Brazil: Tocantins (Tocantins Dr.): INPA 5244 (alc, 124 mm), Rio Araguaia, Laguinho Central, Xambioá (GMS82112404), G.M. Santos, 24 Nov 1982.

Paratypes.—Brazil (Tocantins Dr.): INPA 18628 (1 alc, 162.5 mm), Rio Araguaia INPA ichthyological team, Feb 2000; Goiás: ANSP 185367 (1 alc, 139.0 mm), Lagos do rio Araguaia, near city of Luis Alves, 13°14’S, 050°35’W (FLG94-02), F.L.T. Garro, Sep 1994; MCP 18188 (1 alc, 141.0 mm), same data as ANSP 185367; Tocantins: MZUSP 96328 [ex INPA 20408] (1 alc, 96.0 mm), Caseara Lago Paredão, Rio Araguaia, 09°17’S, 049°58’32”W, J.A. Zuanon et al., 14 Nov 2000.

Diagnosis.—Doras zuanoni is diagnosed among modern congeners by six unique characteristics: 1) gas bladder with two elongate posterior (terminal) diverticula with bases cojoined (Fig. 6H); 2) anterior lateral shoulders of anterior chamber of gas bladder each with a short rounded diverticulum (Fig. 6H); 3) interorbital region wide, 26.7–28.24% of head length; 4) dorsal and ventral procurrent caudal fin rays few, 10; 5) pale midlateral stripe distinct, strongly contrasted with darker sides above and below, beginning near posterior margin of orbit, continuing across tympanal region and finishing along midlateral scutes to caudal fin (Figs. 12B–C); and 6) pale middorsal stripe present from nuchal shield to caudal fin. Doras zuanoni is distinguished from fossil species †Doras dioneae by having a shallow postcleithral process, depth 3.31–3.78 (vs. 2.75) times into oblique length.

Comparisons.—Other species of modern Doras have gas bladder with two posterior diverticula subterminal with bases separate (D. phlyzakion; Fig. 6G)) or with a single terminal diverticulum (D. carinatus, D. micropoeus, D. higuchii; Figs. 6A–F); shoulders of anterior chamber of gas bladder smooth, lacking diverticula; interorbital relatively narrow, width 12.46–24.03% of head length; dorsal and ventral procurrent caudal fin rays more numerous, 12–16; pale midlateral stripe absent or weakly evident and restricted to midlateral plates; and pale middorsal stripe absent.

Description.— Morphometrics and meristics summarized in Table 6; aspects of postcleithral process summarized in Table 1. Largest specimen examined 162.5 mm SL (INPA 18628). Body comparatively stout, deepest at dorsal-fin origin, gently tapering to short, slender caudal peduncle. Ventral surface flattened from snout to anal-fin origin. Head large and deep with short conical snout; dorsal profile straight to weakly concave from snout tip to between anterior and posterior nares, then curving gently (convex) to middle pitline of supraoccipital, usually finishing with low rounded (convex) hump along nuchal shield. Eyes large (24.36–27.76% of head length), covered by thin skin (adipose eyelid not distinct), positioned high on the head and slightly anterior to midpoint between snout tip and dorsal-fin origin; dorsal margin of orbit strongly concave; interorbital comparatively wide (26.7–27.76% of head length).

Mouth small, subterminal; gape with rounded (concave) anterior (premaxillary) margin, straight to weakly concave posterior (dentary) margin. Teeth absent from premaxillae. Each dentary edentate (one specimen, SL 162.5 mm) or with 3–5 acicular teeth in single row (holotype, SL 124 mm).

Anterior and posterior nares separate, surrounded by short tubular skin; posterior nare larger than anterior, located more or less at midpoint between anterior nare and anterior margin of eye; anterior nare closer to posterior nare than snout tip. Cephalic shield weakly ornamented; middorsal furrow on posterior supraoccipital and nuchal shield largely absent, but partially evident in one specimen (ANSP 185367, SL 139 mm), beginning at middle pitline of supraoccipital and finishing before suture between anterior and middle nuchal plates. Cranial fontanel with single opening anterior to epiphyseal bar (portion posterior to epiphyseal bar occluded). Fontanel elongate, narrow, widest posteriorly with rounded margin, attenuate anteriorly; enclosed posteriorly and laterally by frontals, anteriorly by mesethmoid, and set in shallow bony furrow that continues posteriorly onto anterior supraoccipital, finishing at or just before middle pitline. Nuchal foramina absent. Nuchal portion of cephalic shield slightly to sharply elevated forming rounded hump and roof-shaped, forming transverse angle. Anterior nuchal plate well-developed, subpentagonal to subhexagonal, wider than long and sharing broad lateral suture with epioccipital. Mesethmoid elongate, anterior end attenuate with pointed tip. Infraorbital one (lacrimal) comparatively short, anterior end evenly tapered and extending relatively short distance beyond mesial concavity for anterior nare (compare Fig. 4A). Epioccipital posterior process long, ribbon-like, twisted from horizontal plane (anteriorly) to vertical plane (posteriorly), weakly expanded posteriorly and contacting posterior nuchal plate.

Three pairs of barbels: maxillary, inner and outer mental. Maxillary barbel long, tip finishing more or less at medialmost point of gill opening; fimbriate along lateral margin; proximal fimbriae rugose with papillae. Mental barbels nearly equal in size, finishing about halfway between anterior margin of lower jaw and medialmost point of gill opening, bases thick, moderately ornamented with fleshy papillae. Lips fleshy, surfaces with low rounded papillae near insertion of maxillary barbels.

Pectoral girdle in ventral view subtriangular; elongated anteriorly with convergent lateral margins of paired symphyseal (horizontal) limbs of cleithrum long, straight. Anteriormost margin of pectoral girdle bluntly rounded (convex). Transverse limb of coracoid with distinct posterior process (keel) relatively short, extending slightly beyond posterior insertion of pectoral fin. Distal ends of posterior coracoid processes with weak ornamentation (ridges) visible beneath thin skin. Remaining ventral surfaces of pectoral girdle covered with slightly thicker skin.

Postcleithral process blade-like, long and shallowly subrectangular (depth 3.31–3.78 times into oblique length); margins entire, without conspicuous dentations (Fig. 2H). Free dorsal margin straight to weakly concave; dorsal posterior corner usually distinct; ventral margin nearly straight from shoulder to ventral posterior corner of process. Lateral surface of postcleithral process with three longitudial fields of ornamentation usually evident, as described for D. carinatus except ornamentation more granular and middle field narrower.

Skin relatively smooth except for minute punctate tubercles scattered on head, body and fins. Elongate slit-like pore in axillary of pectoral fin. Skin beneath entire length of postcleithral process perforated with numerous smaller round pores imparting a sponge-like appearance. Small pores present in skin above and below anterior midlateral scutes. Ventral surfaces with conspicuous pores, a few in skin on breast in small patch near ventral medial insertion of gill flap, also scattered on abdomen becoming more abundant in pelvic region and around vent (Fig. 3B).

Dorsal fin I,6 (n = 5); pectoral fin I,8 (5); pelvic fin i,6 (5), anal fin modally iv,8, range iii–v,8 (4); caudal fin i,7/8,i (5) with dorsal and ventral procurrent rays modally 10 (5). Dorsal-fin origin located more or less two-fifths SL from snout tip. Morphology of fins as described for D. carinatus except pectoral fin spines with teeth along entire anterior margin.

Lateral line ossified with a complete series of 30–32 midlateral scutes (modally 31; n = 5); morphology largely as described for D. carinatus except midlateral scutes with posterior margins serrated, and depth of midlateral scutes about one-third to one-fourth corresponding body depth at pelvic-fin origin.

Gas bladder large, cordiform, with paired posterior chambers longer than single anterior chamber (Fig. 6H). Each posterior chamber with elongate, finger-like terminal diverticulum; bases of terminal diverticula cojoined, distal ends separate, divergent. Anterior lateral shoulders of anterior chamber each with short rounded diverticulum.



Coloration.—Dorsal and lateral surfaces of head and body with dark gray-brown (preserved) to black (live) ground color; distinct pale stripe begins near posterior orbit, continues across tympanal region and along midlateral scutes to caudal fin; narrower pale middorsal stripe from nuchal shield to caudal fin (Fig. 12B–C). Ventral surfaces and ventralmost sides of body and head completely pale, white. Maxillary barbels dark, gray-tan to black; jaw barbels pale, white. Dorsal fin partially depigmented along base and on dorsal spine; dark blotch on posterior half of fin. Pectoral-fin spine pale, relatively depigmented; rays and membranes dark. Pelvic fins dusky with melanophores more concentrated on membranes. Anal fin with base and anterior margin pale, remaining portion dusky with melanophores more concentrated on membranes.

The contrasting black and white coloration of D. zuanoni closely resembles that of the unrelated doradid genus Platydoras. Carvalho et al. (2003) described daytime interactions wherein juvenile Platydoras were observed cleaning the piscivorous characin Hoplias in a tributary of the Rio Araguaia. They hypothesized the strongly contrasting black and white coloration of Platydoras to signal its recognition as a cleaner. It is unknown whether such coloration similarly serves the sympatric D. zuanoni.



Distribution and habitat.—Doras zuanoni is known from the lower to middle Rio Araguaia, the largest tributary of Rio Tocantins in east-central Brazil. This species, like D. phlyzakion, appears to prefer lentic habitats.

Etymology.—Species named in honor of Jansen Alfredo Sampaio Zuanon for his extensive and valuable contributions to the collection, taxonomy and natural history of neotropical fishes, including discovery of this species.
DISCUSSION
Doras contains one fossil species and five modern species of which three of the latter are herein described as new. The five modern species are separated into two phyletic and putatively monophyletic groups, the phlyzakion group composed by D. phlyzakion (Solimões-Amazon tributaries) and D. zuanoni (Araguaia-Tocantins drainage), and the carinatus group composed by D. carinatus, D. micropoeus (both Atlantic coast drainages of the Guianas, the former also in a right-bank tributary of lower Orinoco), and D. higuchii (lower Amazon tributaries). The two groups are defined by the following set of seven characteristics: 1) midlateral scutes 30-32 in phlyzakion group vs. typically 33-36 in carinatus group, 2) skin on ventral surfaces with many small conspicuous pores especially on abdomen and surrounding vent in phlyzakion group vs. pores absent or restricted to skin surrounding vent in carinatus group, 3) infraorbital one (lacrimal) short, not extending far beyond mesial concavity for anterior nare in phlyzakion group vs. infraorbital one elongate, extended well beyond mesial concavity as attenuate wing in carinatus group, 4) teeth along anterior margin of pectoral spine present to tip in phlyzakion group vs. teeth usually absent from distalmost tip in carinatus group, 5) pectoral girdle with symphyseal (horizontal) limbs of cleithrum having convergent lateral margins straight and anteriormost margin bluntly rounded (convex) in phlyzakion group vs. lateral and anteriormost margins concave in carinatus group, 6) dentition reduced, premaxillae edentate and each dentary with 15 or fewer acicular teeth in phlyzakion group vs. each premaxillae typically with 1–9 acicular teeth and each dentary with patch of 10–60 acicular teeth in carinatus group, 7) gas bladder with two posterior finger-like diverticula in phlyzakion group vs. posterior diverticula asymmetrical, one side absent or grossly reduced and fused, effecting single terminal diverticulum in carinatus group. The occurrence of numerous pores in the skin on ventral surfaces in the phlyzakion group has not been observed in other species of doradids and may be unique to catfishes. Morphology aside the two groups also are found in different habitats. The phlyzakion group is most often recorded from lentic habitats associated with large low-lying rivers and lakes whereas the carinatus group is typical of lotic habitats in large, relatively upland rivers on the Guiana and Brazilian Shields.

Biogeography.—Sabaj Pérez et al. (2007) hypothesized extinction events for the genus Doras in the Maracaibo and Orinoco river basins based in part on their newly described fossil, †D. dioneae, from the Urumaco Formation, northwestern Venezuela, and the absence of credible records of Doras from the present-day Maracaibo and Orinoco. According to their scenario †D. dioneae inhabited the “Paleo-Amazon-Orinoco”, a large and long-persistent river system that originated far south in western Amazonia and flowed north in the Andean foreland basin to empty into the Caribbean on the northern coast of South America near the present-day exposure of the Urumaco Formation. In the Late Miocene (ca. 8 Ma) the rising mountain divides of the Eastern Andes and Coastal Cordilleras isolated the Caribbean outlet, and the “Paleo-Amazon-Orinoco” river system fragmented into today’s fluvial courses. The present Maracaibo basin represents the lowermost course and outlet (in part) of the “Paleo-Amazon-Orinoco” whereas the modern Orinoco receives waters formerly draining into its middle course. The Amazon and possibly extreme northern headwaters of the Paraná system now drain its upper course eastward and southward, respectively (Sabaj Pérez et al., 2007, and references therein).

Doras remains absent from the present Maracaibo and its extinction from the Miocene precursor to this basin is paralleled by another fossil catfish described from the Urumaco Formation, Phractocephalus nassi (Lundberg and Aguilera, 2003). Based on personal communications with P. Petry and F. Provenzano adult specimens collected in the Paragua, a tributary of the Caroní, itself draining into the lower Orinoco, were examined in this study and identified as D. carinatus, the first confirmed records from the Orinoco basin. Doras remains unknown from the remainder of the Orinoco river system.

The fish fauna of upper Caroní shares common elements with those of the upper Caura (Orinoco drainage) to the west, and the Cuyuní (Essequibo drainage) to the east (Lasso et al., 1991; Machado-Allison et al., 2003). The upper Caroní fauna, however, appears to be relatively distinct from the mainstem Orinoco, its low-lying floodplain and left-bank tributaries (e.g., Meta, Apure) draining into the middle to lower Orinoco. Lasso et al. (1991) used faunal similarities and modern drainage patterns to hypothesize a historical connection between the Caroní and Cuyuní. Specifically, rivers of the Gran Sabana region of southeastern Bolivar State, Venezuela, are thought to have drained northeastward into the upper Cuyuní (Essequibo basin) prior to their capture by the upper Caroní and present incorporation into the Orinoco basin. The occurrence of Doras carinatus in the Caroní basin provides further evidence for historical and sizeable connections between upland rivers currently draining the western Guiana Shield northward into the Orinoco and more eastern rivers (e.g., Cuyuní-Essequibo) draining the Shield directly into the Atlantic Ocean. Taken together the lack of evidence for the occurrence of Doras in left-bank tributaries of the middle to lower Orinoco, the Urumaco fossil †D. dioneae, and the putative course of the “paleo-Amazon-Orinoco” imply an extinction event in a portion of the modern-day Orinoco basin and further distinguishes the fish faunas of its middle to lower left-bank (Andean) and right-bank (Shield) tributaries.



The distributions of the two species groups also imply interesting historical connections. The carinatus group is distributed both north and south of the Amazon channel in rivers draining the Guiana Shield northwards (D. carinatus, D. micropoeus) and southwards (D. higuchii in the Trombetas and Jari) and the Brazilian Shield northwards (D. higuchii in the Xingu). The phlyzakion group, on the other hand, occurs in lowland portions of the Solimões (D. phlyzakion) and Araguaia (D. zuanoni), two regions separated by the Brazilian Shield uplands centered around Serra do Cachimbo and currently inhabited by D. higuchii.
KEY TO MODERN SPECIES OF DORAS


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