Chalceus epakros, Zanata & Toledo-Piza, 2004

Zanata, Angela M. & Toledo-Piza, Mônica, 2004, Taxonomic revision of the South American fish genus Chalceus Cuvier (Teleostei: Ostariophysi: Characiformes) with the description of three new species, Zoological Journal of the Linnean Society 140 (1), pp. 103-135 : 124-132

CHALCEUS EPAKROS SP. NOV. ( FIGS 18–20 , TABLE 4)

Chalceus macrolepidotus (not of Cuvier, 1817), misidentification: de Mérona, Santos & Almeida, 2001: 387 [ Brazil, Rio Tocantins at Tucuruí dam]. Ferreira, 1984: 356 [ Brazil, Pará, Rio Curuá-Una].

Chalceus erythrurus (not of Cope, 1870), misidentification: Regan, 1912: 389 [Rio Cupari, Brazil].

Diagnosis

Chalceus epakros can be readily distinguished from all other Chalceus species with the exception of C. guaporensis by the lack of a median fontanel between the frontal and parietal bones, the presence of a longitudinal dark stripe from the posterodorsal margin of opercle to caudal peduncle and by the relatively longer and more acute snout ( Figs 18 , 19 ). It differs from C. guaporensis by having 8 branched pelvicfin rays (vs. 7 in the latter species, see ‘Remarks’ under C. guaporensis ). Although there is broad overlap in the ranges, the number of lateral line scales in C. epakros tends to be lower than that in C. guaporensis ( Table 6, Fig. 21 ). C. epakros may be further distinguished from C. erythrurus , C. spilogyros and C. guaporensis in having the first small tooth of the inner dentary row located very close to the symphyseal tooth, consequently forming an almost continuous series (vs. first small tooth of inner dentary row located behind fourth to fifth tooth of anterior row with a distinct gap between the symphyseal tooth and first small conical tooth). The central portions of the scales on the longitudinal series above the lateral line are tinged with red in live specimens of C. epakros ( Géry, 1977: 329) (vs. red pigmentation absent in C. erythrurus and C. macrolepidotus ); there is no information about live coloration of C. guaporensis and C. spilogyros ). A humeral spot is sometimes present in C. epakros ( Fig. 19 ), although in this species it is usually round to vertically elongate and located deeper in the skin and thus less conspicuous than those of C. erythrurus and C. spilogyros in which it is located superficially on the skin (see ‘Comments...’, below).

Description

Morphometric data are presented in Table 4. Maximum size 175.6 mm SL. Body robust, somewhat compressed, relatively elongate, greatest body depth slightly anterior to dorsal-fin origin. Dorsal profile of head convex anteriorly on snout region, posterodorsally inclined from anterior end of snout to tip of supraoccipital spine. Anterior profile of head distinctly acute in dorsal view. Interorbital distance wide, proportionally wider relative to body size in larger specimens. Dorsal surface of head in interorbital region flat in specimens around 100 mm SL and smaller and slightly convex in larger specimens. Dorsal body profile convex from tip of supraoccipital spine to dorsal-fin origin. Dorsal body profile posteroventrally inclined along dorsal-fin base, straight to relatively convex to adipose fin and concave along dorsal profile of caudal peduncle to origin of procurrent caudal-fin rays. Ventral profile of head somewhat convex from tip of lower jaw to vertical through posterior limit of isthmus in specimens up to 120 mm SL, straight and posteroventrally inclined in larger specimens. Ventral body profile convex from posterior limit of isthmus to anal-fin origin. Body profile along anal-fin base posterodorsally inclined, slightly concave along ventral margin of caudal peduncle. Smaller specimens have larger head lengths relative to SL. Median fontanel between frontals and parietals absent in all samples including smallest specimens. Mouth terminal, large; upper jaw slightly longer than lower jaw, tip of premaxillary teeth extending below margin of upper lip, giving saw-like appearance to margin of premaxilla even in closed mouth. Maxilla extending to vertical through anterior margin of orbit. Supramaxilla present.

Dorsal-fin rays ii, 10 (ii,10; ii, 9 in one and ii, 11 in two specimens, n = 181). Dorsal-fin origin located posterior to vertical through insertion of innermost pelvic-fin rays. First dorsal-fin pterygiophore inserting behind neural spine of 11th vertebra (n = 2). Distal margin of dorsal fin slightly straight to convex. Adipose fin present. Anal-fin rays iii,9 (iii,9; iii, 8 in 22 specimens, iii, 10 in one specimen, n = 177). First analfin pterygiophore inserting behind haemal spine of 23rd vertebra (n = 2). Distal margin of anal fin straight to emarginate with anterior branched rays approximately 3 times length of ultimate ray. Pectoral-fin rays i,16 (range 14–17, 12 in one and 13 in three specimens, respectively, mean 16.1, n = 175), pointed distally, with unbranched- and first branched rays longest, not reaching pelvic-fin insertion. Pelvicfin rays i,8 (i,8; i, 7 in 2 specimens, i, 9 in 4; n = 180), pointed distally. Caudal fin forked, lower fin lobe slightly more developed.

Premaxillary teeth in three rows. Outer row 12 (range 9–13, 8 and 14 in one specimen each, mean 10.7, n = 180); tricuspid or pentacuspid, with medial cusp larger and all teeth of similar size. Cusps slightly curved with concave portion facing mouth cavity. Inner row 8 (range 7–10, 6 in 3 specimens; mean 8.0, n = 180); largest, symphyseal tooth usually asymmetric with one cusp on medial margin and two on lateral margin of tooth. Remaining teeth penta- or heptacuspid, with second tooth from symphysis larger and teeth gradually diminishing in size laterally. Cusps slightly curved with concave portion opposite of mouth cavity. Intermediate row 2 (2; 1 in five specimens, 3 in one specimen n = 180) pentacuspid teeth, more widely separated than teeth of other rows and of intermediate size. Cusps straight.

Maxillary teeth 15 (range 9–16, 8 in 2 specimens, 17 in one, mean 12.6, n = 177). Anterior teeth tricuspid or conical posteriorly; teeth extending along almost entire margin of ossification. Dentary teeth in two rows. Outer row 11 (range 10–18, 9 in one specimen, 19 in 2; mean 13.3, n = 178), large and pentacuspid anteriorly, sometimes heptacuspid, gradually diminishing in size and number of cusps posteriorly. Posteriormost teeth conical. Cusps slightly curved with concave portion facing mouth cavity. Inner row teeth consisting of large, conical, symphyseal tooth followed by series of minute conical teeth. First small tooth originating very close to symphyseal tooth and forming an almost continuous series.

Scales cycloid, large overall and approximately twice as large above lateral line as below it. Circuli on exposed portion of scales not concentric with those of anterior portion. Circuli on exposed portion of scales straight and extending to posterior margin of scale in small specimens; disorganized and labyrinthic pattern in specimens around 160 mm SL. Radii originating on centre of scale and radiating anteriorly and posteriorly on scale surface.

Lateral line low on body sides, complete, with alternating large and small perforated scales from posterior margin of opercle to vertical through base of last anal-fin ray; scales smaller and of similar size from that point to end of caudal peduncle. Canals in large specimens with 1–6 branches. Number of branches decreases toward caudal peduncle with posterior scales unbranched. Small specimens (£ 150 mm) with branching pattern less developed. Lateral-line scales 35 (range 31–37, mean 34.3, n = 169). Scale rows between dorsal-fin origin and lateral line 3; between lateral line and pelvic-fin insertion 2. Scales around caudal peduncle 12. Vertebrae 34 (n = 1), 35 (n = 1).

Colour in life. Description based on photographs taken by various collectors, Géry (1977: 329) and personal observation of 3 specimens kept in aquarium. Overall coloration of head and body bright silver. No conspicuous humeral spot. Dorsal portion of eye yellow. Central portions of scales on longitudinal series just above lateral line tinged with red, coloration less evident posterior to vertical through anal-fin origin. All fins (except pectoral) bright red. Pectoral fin hyaline. Three specimens kept in tanks exhibited rapid changes in coloration with fins turning pale under stressful conditions.

Colour in alcohol. Few examined specimens retain guanine and have silvery reflections on body and head. Most only retain silvery pigmentation on infraorbital and opercular regions. Specimens lacking guanine on body yellowish to tan, darker dorsally. Longitudinal dark stripe extends from posterodorsal margin of opercle to caudal peduncle, but not reaching base of caudalfin rays. Stripe formed of dark chromatophores located deep in skin (see ‘Comments...’, below); less evident in specimens retaining guanine on body. Small specimens with inconspicuous vertically elongate humeral spot extending over first three scales of lateral line (see ‘Comments...’, below). Scales above lateral line with chromatophores slightly more concentrated along posterior margin forming fine reticulate pattern. Humeral spot and reticulate pattern progressively less evident in larger specimens. All fins hyaline, some specimens with dorsal and anal fins with scattered chromatophores. Most specimens with dark tips on adipose fin and dorsal- and caudal-fin rays.

Distribution

The species is widespread throughout the central and lower portions of the Amazon basin including the Rio Madeira, Rio Xingu, Rio Tapajós, Rio Negro, Rio Branco, Rio Trombetas and Rio Tocantins-Araguaia basins ( Fig. 20 ). It also occurs in the middle and upper Río Orinoco basin, the Essequibo River in Guyana and in the Río Nanay in Peru (see ‘Remarks’).

Etymology

Epakros , from the Greek for ‘pointed at the end’, referring to the snout of the species.

Remarks

The single specimen of C. epakros (ANSP 175371) from the Essequibo River represents an extension to the north-east relative to the other records of the species. A major extension to the west is represented by samples from the Río Nanay, in the Peruvian Amazon. These samples could not be distinguished from those originating in the more central and eastern portions of the Amazon basin and are consequently considered conspecific despite the gap in the known distribution of the species.

Material examined

Type material. HOLOTYPE: MZUSP 33392 , 1, 132.6 mm SL; Brazil, Pará, Rio Tapajós , São Luís, above Itaituba (4∞25¢S; 56∞10¢W). Collector M. Goulding, 22/Oct/1983 . PARATYPES: MZUSP 76070 , 53 , 1 C & S, 110.1–150.7 mm SL; INPA 18590, 3 , 119.1 – 129.6 mm SL; USNM 368279, 3 , 121.8 – 138.4 mm SL; UMMZ 239931, 3 , 128.4 – 136.2 mm SL; same data as holotype .

Non-type material. BRAZIL: AMAZONAS: INPA 705 , 2 , 107.5 – 138.1 mm SL. – INPA 16931 , 5 , 129.6 – 148.4 mm SL; Rio Uatumã. – INPA 16965 , 2 , 124.1 – 131.7 mm SL; Rio Uatumã, mouth of Igarapé Catitu. – INPA 16960 , 1 , 162.0 mm SL; INPA 16963 , 2 , 128.0– 145.5 mm SL; Igarapé da Arraia , Rio Uatumã. – INPA 16956 , 1 , 162.0 mm SL; Igarapé da Água Branca , Rio Pitinga. – INPA 18617 , 7 , 112.2 – 141.9 mm SL; Rio Pitinga , Cachoeira Travessão. – MZUSP 6706 , 24 , 93.7 – 156.0 mm SL; Rio Negro , surroundings of Manaus. – MZUSP 31341 , 1, 103.9 mm SL; Rio Negro , Anavilhanas. PARÁ: INPA 16961 , 2 , 143.0 (from 1 spec.), Rio Jari , Igapó and margin of island in front of Porto Sabão. – INPA 16969 , 9 , 135.0– 156 mm SL; Rio Jari , below Cachoeira de Santo Antônio. – INPA 4293 , 2 , 58.5–66.1 mm SL; Rio Xingu , Arroz Cru , Lagoa da Palmeira. – INPA 4181 , 3 , 70.7–72.8 mm SL; INPA 4133 , 2 , 117.1 – 132.9 mm SL; Rio Xingu , Ilha de Babaquara. – MZUSP 33394 , 31 , 125 – 175.6 mm SL; MZUSP 30758 , 1 , 81.6 mm SL; MZUSP 63651 , 3 , 127.0– 146.1 mm SL; Rio Xingu , Belo Monte. – MZUSP 45884 , 1, 125.3 mm SL; Rio Riozinho , Serra de Kukoinhokren. – MZUSP 36816 , 1, 133.3 mm SL; Cachoeira do Espelho , Rio Xingu. – USNM 119949 , 3 , 98.1–178.8 mm SL; Rio Xingu , Porto de Moz. – INPA 6746 , 3 , 136.0–158.0 mm SL; Rio Jamanxim , tributary of Rio Tapajós , Ilha Terra Preta. – MZUSP 22095 , 4 , 86.4–95.3 mm SL; Rio Tapajós , Ilha da Barreirinha , near São Luís. – MZUSP 25431 , 1 , 88.4 mm SL; right margin of Rio Tapajós , in front of Pimental. – MZUSP 30750 , 3 , 127.0–133.0 mm SL; Rio Tapajós , between Itaituba and São Luís. – CAS 69080, 1 , 88.5 mm SL; Rio Tapajós , Itaituba . – MZUSP 25503 , 2 , 102.9 – 108.5 mm SL, left margin of Rio Tapajós , between National Park headquarters and branch of Saita, km 67. – MZUSP 30754 , 14 , 1 C & S, 69.3–94.7 mm SL; Rio Tapajós , Pederneiras. – MZUSP 21992 , 4 , 114.4 – 128.5 mm SL; Rio Tapajós , São Luís, Poça de Pedra. – MZUSP 20276 , 8 , 103.8 – 115.6 mm SL; Rio Tapajós , inland lake in front of Monte Cristo. INPA 748 , 1, 133.7 mm SL; Rio Curuá-Una. – INPA 16945 , 1 , 99.4 mm SL; INPA 16946 , 2 , 104.2 – 106.5 mm SL; INPA uncat., 10, 93.6–101.7 mm SL; Icangui, Rio Tocantins. – INPA 16947 , 21 , 79.1–103.8 mm SL; Rio Tocantins, below Tucuruí dam. – MZUSP 30751 , 1, 133.2 mm SL; Rio Itacaiunas , Rio Tocantins, Caldeirão. – MZUSP 20364 , 2 , 71.5–77.2 mm SL; on marginal lagoons of Rio Tocantins, near Tucuruí. – MZUSP 20649 , 2 , 74.4–74.6 mm SL; Igarapé Muru, Rio Tocantins, below Tucuruí. – MZUSP 20324 , 2 , 71.9 –77.0 mm SL; Igarapé Urubu, Rio Tocantins, near Posto Trocará. – MZUSP 20088 , 2 77.8–97.5 mm SL; Rio Trombetas , Oriximiná. – INPA 16968 , 2 , 135.2 – 137.1 mm SL; INPA 16959 , 4 , 105.2 – 116.4 mm SL; Rio Trombetas , below Cachoeira Porteira. INPA 16948 , 5 , 131.7 – 144.4 mm SL; Rio Trombetas , above Cachoeira Porteira. – CAS 69075, 1, 102.5 mm SL; Rio Amazonas , market at Santarém. – CAS 69077, 3 , 108.0– 115.3 mm SL; Rio Amazonas , Marabá. GOIÁS: MZUSP 54571 , 1 , 132.0 mm SL; Rio Tocantins, Minaçú, Porto do Garimpo , below Serra da Mesa dam. – MZUSP 54572 , 2 , 105.3 – 122.3 mm SL; Rio Tocantins, Porto do Garimpo , below Serra da Mesa dam. MATO GROSSO: MZUSP 64960 , 3 , 118.0– 130.3 mm SL; Ribeirão Suaizinho near Fazenda Cascavel, tributary of Rio Suiá-Missu , Rio Xingu. – INPA 16970 9, 87.6– 99.0 mm SL; Rio do Côco , Caseara, Lago do Case. INPA 18602 , 1 , 89.5 mm SL, Rio do Côco ; Caseara, Cantão. – INPA uncat., 21, 84.5–99.8 mm SL; Rio Araguaia , Fazenda Santa Fé. – INPA 18604 , 4 , 91.3– 104.3 mm SL; Lago Santa Fé, Rio Araguaia ; Cantão State Park . – INPA 18603 , 1 , 98.4 mm SL; Lago Ariranhas. – INPA 18605 , 3 , 87.6–88.2 mm SL; Porto Balsa, Rio Côco. – MZUSP 63650 , 3 , 117.4 – 125.7 mm SL; Rio Correntes , Rio Araguaia , Barra do Garça. – MZUSP 19631 , 3 , 73.9–108.8 mm SL; Rio Araguaia , Santa Terezinha. – MZUSP 3847 , 1, 107.7 mm SL; Rio Araguaia. – MZUSP 64202 , 5 , 138.8 – 165.3 mm SL. – MZUSP 54445 , 1, 109.1 mm SL; Rio Cristalino , Rio Araguaia. – MZUSP 62535 , 4 , 124.6 – 138.8 mm SL; Rio Teles Pires , Pesqueiro do Dentinho , município de Alta Floresta – USNM 31083 , 5 , 132.9 –173.0 mm SL; Rio Batovi , small tributary and shallow lake drainage, Rio Xingu. Rondônia: INPA 16925 , 3 , 105.6 – 140.2 mm SL; Rio Jamari , c. 5 km above Samuel dam. – INPA 16967 , 1 , 79.9 mm SL; Rio Urupá , tributary of Rio Jiparaná (= Rio Machado ). – INPA 16966 , 2 , 110.8 – 114.9 mm SL Rio Urupá , tributary of Rio Machado , c. 10 km above Jiparaná; INPA 16957 , 2 , 158.0 mm SL; Lago Espanha, below Samuel dam. – INPA 16962 , 2 , 139.0–158.0 mm SL; Igarapé Japiim, c. 45 km above Samuel dam. – MZUSP 14032 , 5 , 129.6 – 167.3 mm SL; Lago do Paraíso , Rio Machado , Rio Madeira. – MZUSP 77270 , 1 , 89.3 , Panelas, Rio Roosevelt , above falls. RORAIMA: MZUSP 30752 , 1, 128.3 mm SL; Cachoeira do Bem-Querer , Rio Branco. – MZUSP 30749 , 5 , 108.1 – 144.6 mm SL; Rio Uraricoera , Maracá. – INPA 8113 , 1 , 74 , 7 mm SL; Igarapé number 1 .

COLOMBIA: AMNH 38183, 1, 118.9 mm SL, C&S; Amazon Basin.

GUYANA: ANSP 175371, 1, 89.3 mm SL; Essequibo River, sandbars 1.0–1.5 h upstream from Maipuri campsite.

PERU: LORETO: USNM 280438, 2, 67.3–77.1 mm SL; Río Nanay, c. 20 km upstream of mouth in the main channel. – USNM 280440, 1, 64.9 mm SL; Río Nanay, north-east of Iquitos. – USNM 240442, 1, 76.6 mm SL; Río Nanay at Nanay beach, West of Iquitos. – ANSP 167068, 1, 69.8 mm SL; Río Nanay, right bank, 0.5 mi below Santa Clara. – ANSP 167067, 2, 71.8–76.6 mm SL; Río Nanay, creek tributary of Río Nanay (above confluence) c. 0.25 mi below Santa Clara. – ANSP 136900, 5, 73.0– 86.3 mm SL; ANSP 136901, 5, 70.8–86.3 mm SL; Vicinity of Iquitos, Moronacocha outlet, right bank of Río Nanay, c. 9 min above Río Amazonas.

VENEZUELA: AMAZONAS: ANSP 161222, 1, 121.3 mm SL; Río Orinoco at playa across from mouth of Río Iguapo. – ANSP 161224, 1, 130.3 mm SL; Caño of Río Casiquiare, playa c. 1.5 h. from confluence of Río Casiquiare and Río Orinoco. – ANSP 159781, 1, 79.7 mm SL; Río Orinoco at El Burro. – ANSP 161219, 1, 130.1 mm SL; Río Orinoco, caño separating island and playa just downstream from Quiratare. BOLIVAR: ANSP 135641, 2, 71.8–89.1 mm SL; Caño Chuapo, c. 20 min downstream from Jabillae on Río Caura. – ANSP 139554, 5, 88.9–99.0 mm SL; isolated backwater of Río Nichare, c. 10 min from Río Nichare/Río Caura junction. – ANSP 159779, 1, 94.0 mm SL; Río Orinoco, vicinity of Puerto Las Majadas, Río Orinoco/ Río Caura confluence. – ANSP 159780, 2, 92.1– 101.3 mm SL; Río Caura at Puerto das Majadas. – ANSP 139559, 1, 119.5 mm SL; sand bar along Río Mato.

CHALCEUS GUAPORENSIS SP. NOV.

( FIGS 21–23 ; TABLE 5)

Chalceus erythrurus (not of Cope, 1870) – misidentification: Chang, 1998: 22 [ Peru, Río Madre de Dios basin, Río Malinowski; (specimen not examined, identification inferred by geographical distribution)]. Ortega, 1996: 464 [ Peru, Río Manu system].

Chalceus sp. Lauzanne & Loubens, 1985: 108 [ Bolivia, Rio Mamoré basin (specimen not examined, identification inferred by geographical distribution)].

Diagnosis

Chalceus guaporensis can be readily distinguished from all other Chalceus species except C. epakros by the lack of a median fontanel between the frontal and parietal bones, by the relatively longer and more acute snout and by the presence of a longitudinal dark stripe from the posterodorsal margin of opercle to caudal peduncle formed by chromatophores located deep in the skin (see ‘Comments...’, below) ( Figs 22 , 23 ). Chalceus guaporensis differs from C. epakros in having 7 branched pelvic-fin rays (vs. 8 in the latter species, see ‘Remarks’). It may be further distinguished from C. epakros and C. macrolepidotus in having the first small tooth of the inner dentary row located behind the fourth or fifth tooth of the anterior row with a distinct gap between the symphyseal tooth and first small conical tooth (vs. first small tooth of inner dentary row located very close to the symphyseal tooth and forming an almost continuous series). Chalceus guaporensis also has a somewhat rounded, conspicuous humeral spot extending over the first four scales of the lateral line and located deep in the skin (see ‘Comments...’, below).A humeral spot located deep in the skin is sometimes present in C. epakros , although when present in the latter species it is usually more vertically elongate than the spot of C. guaporensis . Although there is broad overlap in the ranges, the number of lateral line scales in C. guaporensis tends to be higher than those in C. epakros ( Table 6, Fig. 21 ).

Description

Morphometric data presented in Table 5. Maximum size 140.4 mm SL. Body robust, somewhat compressed, relatively elongate, greatest body depth located slightly anterior to dorsal-fin origin. Dorsal profile of head convex anteriorly at snout region, posterodorsally inclined from anterior end of snout to tip of supraoccipital spine. Anterior profile of head distinctly acute in dorsal view. Interorbital distance wide, proportionally wider relative to SL in larger specimens. Dorsal surface of head in interorbital region flat. Dorsal body profile convex from tip of supraoccipital spine to dorsal-fin origin. Dorsal body profile posteroventrally inclined along dorsal-fin base, then straight to relatively convex to adipose fin and concave along dorsal profile of caudal peduncle to origin of procurrent caudal-fin rays. Ventral profile of head somewhat convex from tip of lower jaw to vertical through posterior limit of isthmus. Ventral body profile convex from that point to anal-fin origin. Body profile along anal-fin base posterodorsally inclined, slightly concave along ventral margin of caudal peduncle. Smaller specimens with relatively longer heads. Median fontanel absent between frontals and parietals even in smallest examined specimens. Mouth terminal, large, upper jaw slightly longer than lower jaw, tip of premaxillary teeth extends below margin of upper lip giving a saw-like appearance to margin of premaxilla even in closed mouth. Maxilla extending to vertical through anterior margin of orbit. Supramaxilla present.

Dorsal-fin rays ii,10 (ii,10; ii, 9 in one and ii, 11 in two specimens, n = 70). Dorsal-fin origin situated posterior to vertical through insertion of innermost pelvic-fin rays. First basal dorsal-fin pterygiophore inserting behind neural spine of 11th vertebra (n = 3). Distal margin of dorsal fin slightly straight to convex. Adipose fin present. Anal-fin rays iii,9 (iii,9; iii, 8 in 2 specimens, n = 70). First basal anal-fin pterygiophore inserting behind haemal spine of 24th vertebra (n = 4). Distal margin of anal fin straight to emarginate with anterior branched rays approximately 3 times length of ultimate ray. Pectoral-fin rays i,14 (range 14–16, 17 in one specimen, mean 16.1, n = 70), pointed distally, with unbranched- and first branched rays longest, but not reaching pelvic-fin insertion. Pelvic-fin i, 7 (i,7, n = 70); fin pointed distally. Caudal fin forked, lower fin lobe slightly more developed than upper lobe.

Premaxillary teeth in three rows. Outer row 9 (range 9–12, mean 10.8, n = 68); teeth tricuspid, sometimes pentacuspid, with medial cusp larger and teeth of similar size. Cusps slightly curved with concave portion facing mouth cavity. Inner row 8 (range 7–10, 11 in 1 specimen; mean 8.5, n = 70) largest, symphyseal tooth usually asymmetric with one cusp on medial margin and two cusps on lateral margin of tooth. Remaining teeth pentacuspid, or more lateral teeth tricuspid, with second tooth from symphysis larger and teeth gradually diminishing in size laterally. Cusps slightly curved, with concave portion opposite of mouth cavity. Intermediate row 2 (2; 1 in one specimen, n = 70) pentacuspid or tricuspid teeth, more widely separated than teeth of other rows and of intermediate size. Cusps straight.

Maxillary teeth 11 (range 9–16, 17 in one specimen, mean 12.5, n = 70). Anterior teeth tricuspid with remaining teeth conical. Teeth extending along almost entire margin of ossification. Dentary teeth in two rows. Outer row 14 (range 11–16, 18 in one specimen; mean 13.1, n = 70), with teeth large and pentacuspid anteriorly, sometimes heptacuspid, gradually diminishing in size and number of cusps posteriorly. Posteriormost teeth conical. Cusps slightly curved with concave portion facing mouth cavity. Inner row consists of large conical symphyseal tooth followed by series of minute conical teeth. First tooth usually positioned behind fourth or fifth tooth of anterior row with distinct gap between that tooth and symphyseal tooth.

Scales cycloid, large overall and approximately twice as large above lateral line as below it. Circuli on exposed portion of scales not concentric with those of anterior portion. Circuli on exposed portion of scales straight and extending to posterior margin of scale in examined specimens. Radii originating on centre of scale and radiating anteriorly and posteriorly on scale surface.

Lateral line low on body sides, complete, with alternating large and small perforated scales from posterior margin of opercle to vertical through last anal-fin ray; scales smaller and of similar size from that point to end of caudal peduncle. Canals in large specimens with 1– 5 branches. Number of branches decreases toward caudal peduncle, with posterior scales unbranched. Small specimens with branching pattern less developed. Lateral-line scales 36 (range 35–37, 1 specimen with 34, 1 with 38; mean 36.1, n = 69). Scale rows between dorsalfin origin and lateral line 3. Scale rows between lateral line and pelvic-fin insertion 2. Scales around caudal peduncle 12. Vertebrae 35 (n = 3).

Colour in alcohol. Specimens only retain silvery pigmentation on infraorbital and opercular regions. Body tan, darker dorsally. Longitudinal dark stripe formed by dark chromatophores located deep in the skin (see ‘Comments...’, below). Stripe extends from posterodorsal margin of opercle to caudal peduncle, but not reaching base of caudal-fin rays. Somewhat rounded, conspicuous humeral spot extending over first four scales of lateral line and located more deeply in skin (see ‘Comments...’, below). Dorsal portion of humeral spot overlapping longitudinal stripe. Scales above lateral line with chromatophores slightly more concentrated along posterior margin and forming fine reticulate pattern. Some specimens also have chromatophores scattered on lateral-line scales and one longitudinal series above it. All fins hyaline, with dorsal, anal and adipose with dark chromatophores scattered. Tips of caudal- fin rays and ventral margin of first principal ray of lower caudal-fin lobe dark.

Distribution

The Rio Guaporé and Río Mamoré drainages, Río Madre de Dios and Rio Jaci-Paraná in the upper Rio Madeira (see ‘Remarks’) ( Fig. 20 ) .

Etymology

Named after the Rio Guaporé.

Remarks

The main trait that distinguishes C. guaporensis from C. epakros is the number of branched pelvic-fin rays (7 vs. 8, respectively). Among specimens of C. guaporensis examined in this study ( Table 7, n = 71) all have 7. Additional specimens from Río Madre de Dios basin (MUSM 3756, n = 1; 3907, n = 1; 16850, n = 1; and 8033, n = 5), all have 7 except for one specimen (MUSM 8033) with 8 (H. Ortega, pers. comm.). The latter specimen is considered atypical and herein tentatively identified as C. guaporensis .

Most of the C. epakros specimens (n = 174) have 8 rays ( Table 7). Of the six remaining specimens, two have 7 (INPA 16968, 1 of 2, 137.1 mm SL, from the Rio Trombetas and INPA 16925, 1 of 3, 105 mm SL from the upper Rio Madeira); both belong to lots in which the other specimens have 8 and their number of lateral-line scales (34 and 36, respectively), falls within the range of variation for the two species ( Table 6). The specimens from the Rio Trombetas all possess 8; that basin is, furthermore, distant from the distribution range of C. guaporensis . The specimen with 7 rays from the Rio Trombetas appears atypical and is herein assigned to C. epakros . The specimen from the upper Rio Madeira is somewhat more problematic because it comes from a location adjacent to the northern limit of the distribution range of C. guaporensis , raising the question as to whether C. epakros and C. guaporensis perhaps occur in sympatry along the edges of their distribution range, or whether the specimen is atypical. It was collected in the Rio Jamari, a tributary of the upper Rio Madeira below the waterfall region (a series of 19 waterfalls occurs along a 353-km river stretch between the cities of Porto Velho in the upper Rio Madeira and Guajará-Mirim in the Rio Mamoré; Goulding, 1979: 33–34). Within the Rio Madeira basin, C. epakros appears to occur only in regions downstream of the waterfalls, while all specimens of C. guaporensis from the region of the upper Rio Madeira were collected upstream. Until additional information on these two species becomes available, we have tentatively assigned the specimen to C. epakros .

Material examined

Type material. HOLOTYPE: UMMZ 239851 , 1 , 112.0 mm SL. BOLIVIA: BENI: Río Itenez at mouth of Río Baures , 6 km SW of Costa Marques; 12∞31¢S, 64∞19¢ W. Collector R. M. Bailey & R. Ramos, 30/Sep/ 1964 . PARATYPES: BOLIVIA: BENI: UMMZ 204719 , 4 , 1 DS, 75.0– 128.4 mm SL ; MZUSP 76071 , 3 , 78.1– 84.7 mm SL; same data as holotype . – UMMZ 204209 , 19 , 2 C & S 62.2 –86.2 mm SL ; MZUSP 76072 , 4 62.3– 81.4 mm SL; Río Itenez, opposite Costa Marques , 12∞29¢30¢¢S, 64∞15¢30¢¢W . – UMMZ 204783 9, 2 DS, 75.3–109.9 mm SL; Río Baures , 400 m above mouth on left bank, 6 km SW of Costa Marques ; PERU: MADRE DE DIOS: USNM 319294 , 7 , 1 C & S, 122.3–133.4 mm SL; Manu National Park, Pakitza, Picaflor Stream , Cana Brava Trail # 19 .

Non-type material. BOLIVIA: BENI: UMMZ 205201 , 3 , 70.9–84.9 mm SL; slough of Río Itenez , 10 km SE of Costa Marques (Brazil) . – UMMZ 204272 (2 of 4) 101.8–121.1 mm SL; Río Itenez at mouth of dry run, 2 km SE of Costa Marques (Brazil) . – UMMZ 204447 , 3 , 73.2–78.1 mm SL; Río Itenez , along sand bar about 9 km SE of Costa Marques (Brazil) . – UMMZ 204949 , 1 , 82.5 mm SL; playa pond of Río Itenez , 9 km SE Costa Marques (Brazil) . – UMMZ 204588 , 1 , 67.8 mm SL; Río Itenez , 5 km SW of Costa Marques , 1.5–2 km above mouth of Río Baures . – UMMZ 204848 (1 of 3 specimens examined) 140.4 mm SL; Río Baures , 2 km above mouth . – UMMZ 233932 , 1 , 66.6 Río Baures at mouth, on right bank, 6 km SW of Costa Marques, Brazil. – FMNH 57585 , 2 , 95.0– 97.6 mm SL; Villa Bella . – MNHN 1989–1426 , 2 , 124.2 – 126.3 mm SL. San Luis, Madre de Dios – AMNH 40169 , 1, 102.9 mm SL; Río Mamoré at Cachuela, below Guayaramerin . – AMNH 40059 , 21 , 61.7–124.2 mm SL; Río Baures , 500 m above mouth . SANTA CRUZ: AMNH 77533 , 1 , 83.6 mm SL; Río Mamoré, c. 2 km north of Boca Chapare .

BRAZIL: RONDÔNIA: FMNH 14988–14989, 2, 79.1– 100.8 mm SL; FMNH 57584, 13, 77.3–126.9 mm SL; Rio Guaporensis, Maciel. – INPA 16927 1, 94.0 mm SL; Rio Jaci-Paraná, c. 3 km from town of Jaci-Paraná.

Figures

Figure 18. Chalceus epakros sp. nov., holotype, MZUSP 33392, 132.6 mm SL, Brazil, Pará, Rio Tapajós, São Luís, above Itaituba, 4∞25¢S; 56∞10¢W.

Figure 19. Chalceus epakros sp. nov., INPA 16926, 95.6 mm SL, Brazil, Pará, Rio do Côco, Caseara, Lago do Casé.

Figure 20. Map of northern portion of South America showing geographical distribution of Chalceus epakros (dots, 1 = type locality) and C. guaporensis spp. nov. (triangles, 2 = type locality). Some symbols represent more than one locality or lot of specimens.

Figure 21. Chalceus guaporensis and C. epakros spp. nov. Tukey box plots of the number of lateral line scales. Visual comparison shows that these scale counts are obviously different in the two species. Although overlapping, the counts are significantly different when subject to Mann–Whitney rank-sum tests (t = 13158.5, P <0.001; median: C. guaporensis = 36, C. epakros = 34).

Figure 22. Chalceus guaporensis sp. nov., holotype, UMMZ 239851, 112 mm SL, Bolívia, Beni, Rio Itenez at mouth of Rio Baurés, 6 km SW Costa Marques (Brazil), 12∞31¢S; 64∞19¢W.

Figure 23. Chalceus guaporensis sp. nov., paratype, UMMZ 204783, 80.5 mm SL, Bolívia, Rio Baurés, 400 m above mouth on left bank, 6 km SW Costa Marques (Brazil),12∞34¢6¢S; 64∞19¢W.