(Figs. 1- 4A, 5, 6A; Tab. 1)

Creatochanes gracilisEigenmann, 1908:106 [original description; type locality: rio Tapajos, Brazil].

Bryconops cf. gracilis. -Ferreira, 1993:15, 48, 77 [Brazil, rio Trombetas basin: abundance and distribution].

Bryconops gracilis. -Silva-Oliveira et al., 2019a:3, 8, 12, fig. 7b,c [rio Xingu basin; photo].

Diagnosis. Bryconops gracilis differs from all congeners, except B. alburnoides, by the higher number of branched pelvic- (8 vs. 7) and anal-fin rays (31-36 vs. 19-30), predorsal scales (15-17 vs. 8-14), and lateral-line scales (53-62 vs. 9-49). It is distinguished from B. alburnoides by possessing two rows of premaxillary teeth (vs. three), by having predorsal scales arranged in a regular series (vs. predorsal scales irregularly arranged; Fig. 4B), and an isognathous mouth (vs. upper jaw longer than lower jaw). Additionally, B. gracilis can be diagnosed from B. alburnoides by the coloration of the caudal fin lobes in living specimens (caudal fin with a yellow patch restricted to dorsal lobe vs. both dorsal and ventral lobes fully yellow).

FIGURE 1

Description. Morphometric data presented in Tab. 1. Body elongated, compressed, greatest body depth located just anterior to dorsal-fin origin. Dorsal body profile slightly convex from margin of upper lip to end of supraoccipital spine; from that point to dorsal-fin origin straight and posteroventrally inclined along dorsal-fin base, straight from end of dorsal fin to adipose-fin base, and slightly concave from that point to anterior most dorsal procurrent caudal-fin rays. Ventral profile of head and body slightly convex from lower lip to pelvic-fin origin, and straight from the latter point to anal-fin origin. Ventral profile straight and posterodorsally inclined along anal-fin base. Ventral profile of caudal peduncle slightly concave.

FIGURE 2

TABLE 1

	H	N	Range	Mean	SD
Standard length (mm)	61.8	42	36.4-129.8	94.8	-
Percents of standard length
Snout to dorsal-fin origin	50.2	42	46.9-53.7	50.0	1.5
Snout to anal-fin origin	59.9	42	56.4-65.6	62.2	2.0
Snout to pelvic-fin origin	46.9	42	44.6-49.7	47.5	1.2
Pelvic-fin length	-	31	9.9-14.6	12.8	1.2
Snout to pectoral-fin origin	22.7	42	21.8-26.9	23.4	1.0
Pectoral-fin length	-	31	14.3-21.9	16.8	1.5
Dorsal-fin base length	12.1	42	10.5-13.9	12.1	0.9
Depth at dorsal-fin origin	19.4	42	18.4-24.8	23.0	1.4
Dorsal-fin terminus- adipose origin	25.9	42	24.0-29.2	26.5	1.4
Dorsal-fin origin- adipose origin	38.8	42	35.4-41.2	38.8	1.3
Adipose terminus to hypural plate	10.5	42	10.2-15.0	11.9	1.1
Anal-fin base length	29.1	42	24.7-33.5	30.7	1.7
Caudal-peduncle length	9.7	42	7.8-13.3	10.2	1.1
Caudal-peduncle depth	7.3	31	6.3-8.2	7.3	0.4
Head length	21.0	42	19.6-26.1	21.6	1.4
Maxillary length	9.7	42	8.2-12.4	9.7	0.8
Snout length	6.8	42	4.7-6.9	5.6	0.5
Horizontal orbit diameter	8.1	42	7.3-10.7	8.5	0.8
Percents of head length
Maxillary length	46.2	42	40.2-50.6	45.1	2.5
Snout length	-	42	23.0-28.9	26.1	1.4
Horizontal orbit diameter	38.4	42	35.5-42.7	39.4	1.7
Tip of snout to tip of supraoccipital	92.3	42	91.4-102.4	94.9	2.1
Posterior margin of orbit to end of opercle	-	42	28.9-36.9	33.2	1.8

Mouth terminal (Fig. 2). Posterior extension of maxillary not reaching junction between second and third infraorbital bones; third infraorbital moderately developed, not reaching preopercle ventrally. Supraorbital bone present, not reaching sixth infraorbital posteriorly. Premaxillary teeth in two rows, with central cusp higher than remaining; outer tooth row irregular, with 3 (3), 4* (27) or 5 (21) tri- to pentacuspid teeth; inner tooth row with 4 (2) or 5* (50) penta- to heptacuspid teeth. Maxilla lacking teeth* (51) or with 1 (3) conical tooth. Dentary with 5* (24), 6 (27) or 7 (1) tri-, penta-, or heptacuspid teeth, followed by 1-4 smaller, conical teeth (Figs. 2-3).

FIGURE 3

Dorsal-fin rays ii,9* (54); first unbranched ray about one-half the length of second unbranched ray. Dorsal-fin origin situated posterior to vertical through pelvic-fin origin and near middle of body. Posterior margin of dorsal fin straight to slightly concave. Adipose-fin origin approximately at vertical through 19th or 20th anal-fin branched rays. Principal caudal-fin rays 8+9* (54). Lobes of caudal fin unequal, upper lobe with rounded tip, lower lobe longer and more pointed. Dorsal procurrent caudal-fin rays 10 (1), 11 (2), 12 (1), or 13 (1), ventral procurrent caudal-fin rays 11 (1), 10 (2), 12 (2). Pectoral-fin rays i, 11 (5), 12 (35) or 13 (9). Tip of pectoral fin slightly beyond half the distance between origins of pectoral and pelvic fins. Pelvic-fin rays i,8* (54). Pelvic-fin origin anterior to vertical through first dorsal-fin ray. Anal-fin rays iv,30 (8), 31* (10), 32 (12), 33 (8), 34 (5), 35 (2) or 36 (2). Anal-fin origin posterior to vertical through base of last dorsal-fin ray. Distal margin of anal fin slightly concave, with last unbranched ray and first three branched rays slightly longer than remaining rays.

Scales cycloid, moderately large, with few (5-7) well-marked radii; circuli only present anteriorly. Lateral line with 53 (4), 54* (18), 55 (11), 56 (8), 57 (8), 58 (3), 59 (2), 60 (1) perforated scales until base of caudal-fin rays. Scale rows between lateral line and dorsal-fin origin 8* (49) or 9 (1); scale rows between lateral line and pelvic-fin origin 3 (3) or 4* (48). Predorsal scales 15 (3), 16 (24) or 17 (13) in a regular series (Fig. 4A). Scale rows around caudal peduncle 15 (17) or 16 (26). Precaudal vertebrae 18* (9) or 19 (3); caudal vertebrae 23 (4) or 24 (8); total vertebrae 42 (1), 43* (9) or 44 (2). Supraneurals 8* (14) or 9 (2). First dorsal-fin pterygiophore located between 12th and 13th or between 13th and 14th vertebrae. First anal-fin pterygiophore located between 19th and 20th vertebrae.

FIGURE 4

Total gill rakers of first gill arch 18 (2), 19 (1) or 20 (2); 2 (4) or 3 (1) on hypobranchial, 7 (2), 8 (2) or 9 (1) on ceratobranchial, 1 (5) on cartilage between ceratobranchial and epibranchial, and 8 (4) or 9 (1) on epibranchial. Gill rakers setiform. Branchiostegal rays 4 (5), 3 (5) on anterior ceratohyal and 1 (5) on posterior ceratohyal.

Coloration in alcohol. Overall color of body dark yellow to light brown. Snout, anterior portion of maxilla, dorsal region of head, supraorbital, sixth infraorbital and mid-dorsal region of body dark. Infraorbital bones, posteromedial portion of maxilla, opercle and gular region whitish to yellowish, with few scattered chromatophores. Humeral blotch absent. Dark or silvery midlateral stripe extending immediately behind dorsal portion of opercle to caudal-fin base, slightly more conspicuous at vertical through dorsal fin (Fig. 5).

FIGURE 5

Scales on dorsal and dorsolateral portion of body with chromatophores concentrated at edges, forming slightly reticulate pattern. Ventrolateral scales with scattered chromatophores, not forming reticulate pattern. Dorsal, adipose, pectoral, pelvic and anal fins hyaline with few scattered chromatophores. Caudal pigmented with dark chromatophores, distal half of dorsal and ventral lobes more pigmented, forming black band (Fig. 5).

Coloration in life. Based on freshly captured specimens. Overall body coloration greenish to silvery. Snout and lips light brown. Opercle, infraorbital bones, posteromedial region of maxilla and ventral region of head silvery. Dorsal margin of eye yellow, lateral and ventral margins of eye silvery. Adipose fin yellow. Caudal fin with yellow area at base of dorsal lobe. Dorsal, pectoral, pelvic and anal fins similar to preserved specimens (Fig. 6A).

FIGURE 6

Sexual dimorphism. Mature males of Bryconops gracilis with hooks on pelvic- and anal-fins rays. Pelvic-fin rays with 3-4 small hooks. Anal-fin hooks larger and more numerous (4-8 per ray), present from 3^rd unbranched ray to 15^th branched ray.

Geographical distribution. Bryconops gracilis is distributed across the central and lower Amazon basin, Brazil, and also in the río Ventuari, upper río Orinoco basin in Venezuela (Fig. 7).

FIGURE 7

Material examined. Holotype of Creatochanes gracilis : MCZ 20868, 61.8 mm SL, Brazil, Pará, Santarém, rio Tapajós, Aug 1865, Dexter, James and Talisman (photos, radiographs and CT-Scan only).

Non-type specimens: Brazil: Rio Jari basin: INPA 39220, 3, 25.2-51.7 mm SL, Pará, rio Jari, Monte Dourado, 00°34’15.99”S 52°34’13.98”W, E. Ferreira & S. Amadio, 20 Jun 1987. Rio Maicuru basin: MCP 51813, 5, 30.7-56.3 mm SL; ZUEC 12134, 5, 34.3-56.6 mm SL, Pará, Monte Alegre, rio Maicuru, at road PA-254, 01°36’47.00”S 54°22’37.00”W, R. E. Reis et al., 3 Dec 2015. Rio Madeira basin: INPA 26680, 1, 86.3 mm SL, Amazonas, rio Sucunduri, Apuí, 07°06’11”S 59°41’23”W, L. Rapp Py-Daniel et al., 28 Jun 2016; INPA 40997, 45, 23.3-41.3 mm SL, Mato Grosso, rio Aripuanã, igarapé Praia Grande, Novo Aripuanã, 10°09’19.17”S 59°26’15.21”W, team INPA, 9 Nov 1976. Rio Negro basin: INPA 30701, 1, 103.5 mm SL, Amazonas, rio Negro, rio Carabinari, Novo Airão, 02°01’25.02”S 61°32’35.86”W, L. Carvalho, 25 Out 2004; INPA 37773, 1, 113.9 mm SL, Amazonas, rio Negro, Santa Isabel do Rio Negro, igarapé Darahá, 00°23’9.00”S 67°47’8.00”W, R. de Oliveira, R. Silva & P. Ito, 30 Mar 2012; INPA 43007, 1, 111.3 mm SL, Amazonas, rio Negro, São Gabriel da Cachoeira, Cachoeira Curucui, 00°08’15.84”S 67°05’3.77”W, T. Roberts, A. Oliveira & R. Oliveira, 8 Dec 2013. Rio Tapajós basin: MCP 48844, 2, 51.2-74.7 mm SL, Pará, rio Tapajós, Belterra, 02°45’5.00”S 55°01’12.00”W, W. G. R. Crampton et al., 24 Nov 2013; MCP 52337, 2, 114.6-121.1 mm SL, Pará, rio Arapiuns, Santarém, 02°35’35.91”S 55°28’20.74”W, J. D. Bogotá-Gregory & C. Silva-Oliveira, 14 Nov 2016; INPA 45523, 13, 22.9-31.7 mm SL, Mato Grosso, rio Teles Pires, rio São Benedito, Paranaíta, Mato Grosso, 09°06’13.00”S 57°01’53.00”W, 11 Dec 2012; MZUSP 77712, 1, 70.8 mm SL, Mato Grosso, rio Juruena, 10°27’52.07”S 58°21’27.32”W, F. Machado et al., 26 July 1997; UFOPA-I 679, 4, 52.3-67.1 (2 c&s, 65.4-73.7 mm SL), Pará, rio Arapiuns, Santarém, 02°21’26.78”S 55°03’43.00”W, J. D. Bogotá-Gregory & C. Silva-Oliveira, 26 Nov 2015. UFOPA-I 687, 94.2 mm SL, rio Arapiuns. Santarém, Pará, 02^o24’24”S 55^o10’45”W, C. Silva-Oliveira, J. Bogotá-Gregory & J. Fontenelle, 16 Nov 2016. ZUEC 13907, 2, 90.3-100.5 mm SL, Pará, Santarém, rio Tapajós, lake at Surucuá, 02º53’28”S 55º10’33”W, J. D. Bogotá-Gregory & C. Silva-Oliveira, Nov 2016. ZUEC 13908, 4, 59.0-91.9 mm SL, Pará, Santarém, rio Tapajós, lake at Jaguari, 02º54’6”S 55º04’22”W, J. D. Bogotá-Gregory & C. Silva-Oliveira, Nov 2016. Rio Tocantins basin: MCP 53084, 1, 132.2 mm SL, Maranhão, rio Tocantins, Estreito, 06°50’33.00”S 47°30’29.00”W, Biota Projetos, 25 May 2013; INPA 12316, 1, 106.2 mm SL, Pará, rio Tocantins, Itupiranga, 5°8’12.18”S 49°19’12.62”W, team INPA, 1 Nov 1980; INPA 12404, 5, 76.9-87.7 mm SL, Pará, rio Tocantins, Tucuruí, 03°49’46.40”S 49°36’6.68”W, team INPA, 13 Nov 1981. Rio Trombetas basin: INPA 12394, 4, 94.8-98.8 mm SL, Pará, rio Trombetas, above cachoeira Porteira, Oriximiná, 01°03’59.41”S 57°03’39.49”W, E. Ferreira, 24 May 1988. Rio Uatumã basin: INPA 46124, 32, 103.5-123.3 (3 c&s, 102.2-122.7) mm SL, Amazonas, rio Pitinga, Presidente Figueiredo, 00°53’15.66”S 59°34’25.18”W, J. Birindelli, L. Rapp Py-Daniel, F. Jerep & V. Machado, 19 July 2014. INPA 59629, 5, 68.2-72.3 mm SL, rio Uatumã, Presidente Figueiredo, Amazonas, 01^o54’35”S 59^o27’37”, A. G. Biffi & C. Silva-Oliveira, 20 Jul 2018. Rio Xingu basin: INPA 43319, 1, 111.1 mm SL, Pará, rio Xingu, Porto de Moz, 02°11’0.33”S 52° 08’55.18”W; MZUSP 91304, 1, 87.4 mm SL, Mato Grosso, rio Curisevo, rio Xingu, Gaúcha do Norte, 13°13’10.16”S 53°29’59.98”W, C. Moreira et al., 19 Out 2004; MZUSP 91305, 2, 81.3-103.5 mm SL, Mato Grosso, rio Curisevo, rio Xingu, Gaúcha do Norte, 13°02’5.00”S 53°25’23.03”W, C. Moreira et al., 19 Out 2004; MZUSP 107233, 1, 92.4 mm SL, Pará, Altamira, 03°33’44.56”S 52°21’3.43”W, team UFPA, 12 Dec 2000. Venezuela: Amazonas: Rio Orinoco basin: ANSP 161542, 10 of 20, 27.7-42.6 mm SL, at playa ca. 0.5 km above La Esmerada, 03°09’N 65°32’W, B. Chernoff et al., 12 Mar 1987; ANSP 191228, 5 of 10, 30.7-42.7 mm SL, near mouth of Rio Ventuari, 03°57’29”N 67°01’56”W, M. H. Sabaj et al., 4 April 2004; MZUSP 106371, 1, 27.1-36.8 mm SL, rio Ventuari, 04°12’56.15”N 66°25’21.81”W, J. Birindelli, N. Lujan & V. Meza, 15 April 2010.