Cynopotamus xinguano, Menezes, Naércio A., 2007

Menezes, Naércio A., 2007, A new species of Cynopotamus Valenciennes, 1849 (Characiformes, Characidae) with a key to the species of the genus, Zootaxa 1635, pp. 55-61 : 56-60

Cynopotamus xinguano , new species

Figure 1

Holotype. MZUSP 94009 (100 mm SL), rio Culuene, 13º49’S / 53º15’W, Paranatinga, State of Mato Grosso, Brazil, 21.viii.2006, J.L. Birindelli, L.M. Souza & A. Akama.

Paratypes. Brazil, State of Mato Grosso, MZUSP 91931 (7 specimens, 87.20–132.0 mm SL), taken with holotype; MZUSP 91860 (3 specimens, 128–135 mm SL), Paranatinga, stream at Fazenda do Lúcio, tributary if rio Culuene, 13º50’S / 53º14’W, same collectors as MZUSP 94009, 21.viii.2006; MZUSP 89702 (2 specimens, 100 and 111.50 mm SL), Paranatinga, rio Culuene, 13º49’S / 53º15’W, A. Akama & J.L. Birindelli, 15.i.2006; MZUSP 63436 (14 specimens, 121–160 mm SL), Paranatinga, rio Culuene, Fazenda Columbia, 14º34’S / 53º41’W, F.A. Machado & R.D. O. Calegari, xi.1997; MZUSP 89906 (10 specimens, 87.5–155 mm SL), Gaúcha do Norte, rio Culuene, 13º30’S / 53º05’W, O. Oyakawa, J.L.Birindelli & C. Nolasco, 19.x.2004; MZUSP 90922 (12 specimens, 76–172 mm SL), Gaúcha do Norte, rio Batovi (Tamitaoala), Fazenda Dois Netos, 13º14’S / 54º01’W, same collectors as MZUSP 89906, 21.x.2004; MZUSP 90920 (3 specimens, 94.5- 180 mm SL. Canarana, ribeirão Água Limpa, tributary of rio 7 de Setembro, 10 km south of Canarana, 13º28’S / 52º14’W, same collectors as MZUSP 89906. ANSP 187125 (2 specimens, 140 and 155 mm SL), Canarana, córrego Galheiro, tributary of rio Água Limpa, about 10 km south of Canarana, 13º39’S / 52º16’W, O. Oyakawa, J.L. Birindelli & Oliveira, 17x.2004; MZUSP 31749 (1 specimen, 115.5 mm SL), rio Xingu at meeting of rivers Culuene and Sete de Setembro, M. Goulding, 23.viii.1984. State of Pará: MZUSP 35959 (2 specimens, 93and 124.5 mm SL), rio Fresco, Aldeia Goutine, São Felix do Xingu, Miguel Petrere, viii.1983.

Diagnosis. Cynopotamus xinguano belongs to the group of species characterized by ii, 9 dorsal-fin rays [versus ii, 10 in C. argenteus (Valenciennes) ] and 91–125 perforated lateral-line scales (versus 85–90 in C. juruenae Menezes ) (Menezes, 1976, 1987). It is most similar to C. essequibensis , in number of horizontal rows of scales below lateral line ranging from 17–21, but differs by having more developed gill-rakers on first branchial arch (10–11 versus 8–9 in C. essequibensis ), and the black humeral blotch wider (compare Tables 1 and 2 ). In C. xinguano the first pleural rib and the opening anterior to it are entirely covered by fibers of the obliquus superioris muscle, but the second pleural rib and the obliquus inferioris muscle are visible. In C. essequibensis the first pleural rib and opening anterior to it are visible and the second pleural rib and the obliquus inferioris muscle are totally covered by fibers of the obliquus superioris muscle (compare Figures 2 A and 2B).

Description. Morphometric data of holotype and additional specimens summarized in Table 1 . Meristic and morphometric data based on all lots examined since no statistical differences were found among populations studied from different localities. Body comparatively large (SL = 84–180 mm SL) and anteriorly deep. Dorsal body profile concave at nape, rising sharply in supraoccipital region, strongly convex from this point to dorsal-fin origin, nearly straight along dorsal-fin base, and very slightly convex from dorsal-fin termination to caudal peduncle. Ventral body profile continuously convex from tip of lower jaw to anal-fin origin, straight or nearly so and dorsally inclined along anal-fin base, slightly concave from anal-fin termination to origin of procurrent caudal-fin rays. Snout conical, shorter than orbital diameter. Lower jaw included in upper jaw when mouth is entirely closed. Maxilla extending slightly beyond vertical crossing posterior border of orbit.

Dorsal-fin rays ii, 9. Posteriormost ray branched. Adipose fin present. Anal-fin unbranched rays iv–v (iv), usually iv, branched rays 39–45 (43), 41.4, posteriormost ray split to its base and counted as 1. Weakly developed anterior anal-fin lobe including anterior unbranched rays and first 7–9 branched rays. Anal fin of sexually mature males with bilateral hooks on posteriormost unbranched and posterior part of anterior 12–35 branched rays, the number of hooks per ray ranging from 1 to 20. Pectoral-fin rays i,14–16 (i,14), i,15. Posterior tips of longest pectoral-fin rays reaching beyond pelvic fin origin but not middle of fin. Pelvic-fin rays i,7. No hooks on pelvic-fin rays of sexually mature males. Distal tips of longest pelvic-fin rays not reaching or reaching just slightly beyond anal-fin origin in some specimens. Principal caudal-fin ray count 10/ 9 in all specimens.

Lateral line complete, perforated scales 91–98 (97), 95. Scale rows above lateral line 20–22 (21), 21.4. Scale rows below lateral line 18–20 (20), 19.2. Scale rows around caudal peduncle 27–30 (29), 28.3.

Premaxilla with two rows of teeth: outer row with one anterior canine followed by a series of small conical teeth and one posterior canine; inner row with two conical teeth smaller than anterior canines but slightly longer than conical teeth of outer row. Anterior canine exposed outside anterior border of lower jaw when mouth closed. Outer row small conical teeth 6–8 (7), 7.4. Maxillary teeth 46–63 (52) 54, highly variable in number but no evidence of increase in number with increase in standard length. Dentary with one row of conical teeth of which four anteriormost spaced, third large canine, first and fourth canines about same size and second small conical tooth; these followed by posterior row of close-set smaller conical teeth with no clear evidence of increase in number with increase in standard length. One small conical tooth anterior and slightly internal to first canine. Posterior dentary teeth 24–35 (29), 26.4.

Vertebrae 40–42 (41), 41. Total number of gill- rakers on first branchial arch 10–11 (10), 10.1

Muscular hiatus of pseudotympanum ( Figure 2 B) dorsally limited by lateralis superficialis muscle, posteriorly by exposed portion of second pleural rib, anteroventrally by large portion of obliquus superioris and posteroventrally by small portion of obliquus inferioris; first pleural rib not exposed.

Color in alcohol. Body pale yellow, slightly darker dorsally than ventrally due to presence of dark chromatophores especially along free border of dorsal scales. Snout and upper part of head darker than remaining dorsal surface of body. Premaxilla, anterior part of maxilla and antero-superior part of lower jaw densely pigmented with dark chromatophores. Humeral black blotch slightly elongate vertically, lower portion broader than upper in some specimens, anterior and posterior margins irregularly shaped. Lateral dark body stripe extending from behind upper part of opercle to caudal peduncle where fused to rounded black blotch of caudal base. Lateral body stripe narrower anteriorly and posteriorly, sometimes entirely obscured by guanine. Pectoral, pelvic, dorsal, caudal and adipose fins pale, with scattered dark chromatophores.

Distribution. Cynopotamus xinguano is so far known only from tributaries of the rio Xingu basin ( Figure 3 ).

Etymology. This species is named after the Xinguano an Amerindian tribe living in Parque Indígena do Xingu, a national park in the rio Xingu basin. A noun in apposition.

Figures

FIGURE 1. Cynopotamus xinguano, MZUSP 94009, holotype, 100 mm SL, rio Culuene, Paranatinga, rio Xingu basin, Mato Grosso, Brazil.

FIGURE 2. Schematic drawings of external view of muscles covering the anterior portion of the swim bladder in A— Cynopotamus essequibensis (MZUSP 33433, 129 mm SL); B— Cynopotamus xinguano. (MZUSP 63436, 151 mm SL, MZUSP 91931, 84 mm SL). Anterior towards left; 1 plr (first pleural rib); 2 plr (second pleural rib); os (obliquus superioris muscle); ls (lateralis superficialis muscle); oi (obliquus inferioris muscle). Not drawn to scale.

FIGURE 3. Map of northern and central South America showing the geographic distribution of Cynopotamus xinguano. The open circle includes the type locality and all the other localities around it.

Tables

TABLE 1. Morphometrics of Cynopotamus xinguano. Standard length is expressed in mm; measurements through head length are percentages of standard length; the last four entries are percentages of head length. Specimens are from MZUSP 35959, 91860, 31749, 89702, 91931, 63436, 90922, 89906, 90920 and 90921.

	Holotype	n	range	mean	SD
Standard length	100.0	57	84.0 – 180.0	127.7
Depth at dorsal-fin origin	36.4	57	33.0 – 40.4	35.2	5.0
Snout to dorsal-fin origin	50.8	57	49.0 – 56.3	51.1	1.2
Snout to pectoral-fin origin	30.0	57	26.5 – 31.5	29.2	1.0
Snout to pelvic-fin origin	42.0	57	38.1 – 44.4	41.3	1.1
Snout to anal-fin origin Caudal peduncle depth	58.4 0 8.4	57 57	54.3 – 62.2 0 7.5 – 0 9.3	57.7 0 8.3	1.7 0.3
Caudal peduncle length	0 6.8	57	0 5.7 – 0 8.5	0 7.1	0.6
Pectoral-fin length	19.5	51	16.5 – 21.5	18.6	2.8
Pelvic-fin length	18.4	52	14.4 – 18.7	17.3	0.8
Dorsal-fin base length	12.3	57	12.1 – 14.8	13.1	0.6
Dorsal-fin height	27.3	39	25.0 – 30.7	26.6	4.5
Anal-fin base length	42.3	57	37.3 – 44.1	41.1	1.5
Anal-fin lobe length	16.5	23	14.1 – 19.0	16.5	1.2
Eye to dorsal-fin origin	37.2	57	35.2 – 39.8	37.5	1.2
Dorsal-fin origin to caudal–fin base	54.0	57	52.1 – 56.0	54.0	1.2
Bony head length	29.5	57	28.3 – 32.7	30.0	0.7
Horizontal eye diameter	33.9	57	29.8 – 35.4	32.4	1.3
Snout length	27.1	57	25.3 – 29.0	27.1	0.8
Least interorbital width	21.0	57	18.5 – 22.2	20.0	1.1
Upper jaw length	69.5	57	67.9 – 74.8	67.9	1.5
Humeral blotch maximum width	0 5.3	55	0 5.3 – 0 8.7	0 6.3	0.7

TABLE 2. Morphometrics of Cynopotamus essequibensis. Standard length is expressed in mm; measurements through head length are percentages of standard length; the last four entries are percentages of head length. Specimens are from rio Coppename, Surinam (MZUSP 10659), rio Cupixi, Amapá, Brazil (MZUSP 33419, 33433) and Igarapé do Pau Roxo, Roraima, Brasil (MZUSP 10413, 10414)

Characters	n	range	mean	SD
Standard length	6	106.0 – 165.1	137.3
Depth at dorsal-fin origin	5	33.3 – 37.3	37.6	4.6
Snout to dorsal-fin origin	6	50.2 – 51.5	50.9	0.6
Snout to pectoral-fin origin	6	28.0 – 30.2	29.0	0.8
Snout to pelvic-fin origin	6	40.5 – 42.0	41.3	0.5
Snout to anal-fin origin	5	56.6 – 59.4	58.2	1.1
Caudal peduncle depth	5	8.04 – 8.57	0 8.3	0.2
Caudal peduncle length	5	6.97 – 8.00	0 7.6	0.3
Pectoral-fin length	6	18.0 – 19.4	18.7	0.6
Pelvic-fin length	5	17.5 – 25.0	19.3	3.2
Dorsal-fin base length	6	11.8 – 13.4	12.6	0.5
Dorsal-fin height	6	25.7 – 27.5	26.6	0.7
Anal-fin base length	6	39.6 – 42.5	41.0	1.3
Anal-fin lobe length	4	15.4 – 17.1	16.5	0.7
Eye to dorsal-fin origin	6	35.2 – 38.7	36.9	1.1
Dorsal-fin origin to caudal–fin base	6	53.3 - 56.7	54.6	1.1
Head length	6	29.1 – 30.8	29.8	0.7
Horizontal eye diameter	6	30.9 – 33.6	32.5	1.1
Snout length	6	24.4 – 27.1	26.1	1.0
Least interorbital width	6	18.7 – 19.6	19.4	0.4
Upper jaw length	6	68.7 – 72.8	71.0	1.2
Humeral blotch maximum width	6	0 4.2 – 0 5.2	0 4.5	0.4