Hyphessobrycon otrynus, Benine, Ricardo C. & Lopes, Guilherme A. M., 2008

Benine, Ricardo C. & Lopes, Guilherme A. M., 2008, A new species of Hyphessobrycon (Characiformes: Characidae) from río Portuguesa, río Orinoco basin, Venezuela, Zootaxa 1747, pp. 61-68 : 62-67

Hyphessobrycon otrynus new species

( Table 1 , Figs. 1–4 )

Holotype. USNM 349418, 30.1 mm SL. Venezuela, Portuguesa, río Portuguesa drainage, río Las Marias, at Quebrada Seca, aproximatelly 45 min upstream by car from Highway 5, 22 km NNW Guanare. J. Armbruster and O. Leon. 28 Feb. 1998 (fig. 1).

Paratypes. All from Venezuela. USNM 392814, 29.7mm SL (same data as holotype); LIRP 6040, 8 specimens, 21.5–25.7 mm SL, and 2 specimens C&S, 24.0– 24.2 mm SL, Caño Falcon, río Portuguesa, J. N. Baskin. 24 Nov. 1974.

Diagnosis. This species is distinguished from all other known congeners, except for H. diancistrus , by the presence of two very large bony hooks (in adult males) curving dorsally on each side of anal fin, and caudalfin rays black at distal third of their length (distal tips of caudal-fin rays hyaline). Hyphessobrycon otrynus is promptly distinguished from H. diancistrus by possessing iv,19–21 anal fin rays, versus iv,14 anal-fin rays in the latter. Adult males of H. otrynus are also distinguished from H. diancistrus by presenting very small analfin hooks, lacking from the latter species. Moreover, in H. otrynus , the very large bony hooks are located on the fourth or fifth segments of the last unbranched anal-fin ray and on the fifth segment of the first branched anal-fin ray, whereas in H. diancistrus the bony hooks are located on the first and third segments of the last unbranched and first branched anal-fin rays.

Among small characins, Hyphessobrycon otrynus is most similar to Moenkhausia bonita and Hemigrammus marginatus , from which it differs in having a naked caudal-fin (vs. a scaled caudal-fin), by presenting two large hooks on anal-fin of adult males (not observable in latter species), and ii,8 dorsal-fin rays (vs. ii,9 dorsalfin rays). Hyphesssobrycon otrynus is also distinguished from M. bonita in having an incompletely pored lateral line (vs. completely pored lateral line).

Description. Morphometric data for Hyphessobrycon otrynus are summarized in Table 1 . Body fusiform. Greatest body depth at dorsal-fin origin. Dorsal profile of head straight or slightly convex. Dorsal profile of body slightly convex from posterior tip of supraoccipital spine to dorsal-fin origin, straight or slightly convex and posteroventrally slanted along dorsal-fin base, straight or slightly convex from end of dorsal-fin base to end of adipose-fin, and slightly concave along caudal peduncle. Ventral body profile convex from anterior tip of lower jaw to caudal-peduncle origin, slightly concave along caudal peduncle. Pelvic region transversally flattened, more so proximal to pelvic-fin insertion, becoming somewhat obtuse toward anal-fin origin.

Mouth terminal. Jaws equal or lower jaw slightly longer than upper jaw. Most posterior margin of maxilla trespassing vertical through anterior margin of orbit. Premaxillary teeth in two rows; outer tooth row with 3 (4), 4* (6) conical to tricuspid teeth, midcentral cusps longer than others; inner tooth row with 5 tri to pentacuspid teeth in all specimens, midcentral cusps longer than others. Maxillary with 0 (2) and 1*(8) conical tooth. Dentary with 4 tri to pentacuspid teeth followed by a smaller tricuspid one, and a short series of small conical teeth in all specimens (fig. 2). Palatine and pterygoid bones toothless.

Frontals contact each other at their anterior one-fifth and at epiphyseal bar. Parietal bones completely separated by frontal-parietal fontanel. Infraorbital series well ossified.

Nostrils closer to anterior orbital margins than to each other. Supraoccipital process short, its posterior tip not reaching the vertical through posterior margin of opercle.

Dorsal-fin rays ii, 8 in all specimens. Pectoral-fin rays i,10,i in all specimens. Distal tip of pectoral fin slightly trespasses vertical through pelvic-fin insertion. Adipose fin present. Pelvic-fin rays i, 7 in all specimens; when adpressed, its tip reaches base of second branched anal-fin ray. Anal-fin rays v,19(6) or 21*(4). Principal caudal-fin rays i,17,i. Caudal-fin forked.

Scales cycloid, with few radii along posterior border. Lateral line incomplete, pored scales 8* (2), 9 (1), 12(3). Lateral series of scales including lateral-line pored scales 31*(3), 32(3). Scale rows between dorsal-fin origin and lateral line 5; scale rows between lateral line and pelvic-fin origin 3. Scale sheath along anal-fin base in a single series of 4 scales, extending posteriorly up to fourth branched anal-fin ray.

First gill arch with 13(4), 14*(5) gill rakers on ventral limb and 7(1), 8*(9) on dorsal limb. Total vertebrae 33, supraneurals 5 (fig.3).

Sexual dimorphism. Adult males with two very large, dorsally curved hooks on both sides of anal fin, somewhat buried in thick tissue; anterior hook longest, being a process of the fifth (last unbranched) anal-fin ray; posterior hook being a process of sixth (first branched). Small hooks are located on the distal segments of most anterior anal-fin rays, more concentrated on the segments of the posterior branch of each hooked ray (figs. 3, 4). All small hooks are backward pointed and varying in number from one to four per ray segment. One individual also presented a somewhat more developed hook on each side of the second and third branched anal-fin rays.

Color in alcohol. Overall coloration pale yellow. A dark stripe extending along horizontal septum, more intense from vertical passing through the origin of the second scale most anterior to dorsal fin. Median dorsal scale row, from nape to dorsal caudal-fin origin, densely scattered with dark chromatophores. Anterior to dorsal-fin end, scales of second and third scale rows ventral to median dorsal scale row posteriorly emarginated by dark chromatophores, with pigment concentration diminishing downward. From dorsal-fin end to adiposefin origin, scales of row immediately ventral to median dorsal scale row posteriorly emarginated by dark chromatophores. Very few chromatophores scattered on opercle. Lateral line sensorial canals bordered by few dark chromatophores. Limits of caudal epaxial and hipoaxial, and anal-fin inclinator muscle masses, partially outlined by dark chromatophores (see fig.1). Caudal peduncle with a somewhat horizontal lozenge-shaped black blotch that faint toward distal tips of middle caudal-fin rays.

Head with a dense field of dark chromatophores in region just posterior to epiphyseal bar. Sparsely scattered dark chromatophores anterior to epiphyseal bar. A dense patch of dark chromatophores dorsal to snout, between and surrounding area of nostrils, premaxillary bones and dorsal portion of maxillary bones. A dense patch of dark chromatophores on symphyseal area of dentary bones. A thin line of dark chromatophores bordering orbits. Remainder of head pale yellowish white.

Dorsal fin with scattered dark pigments bordering rays along their length. Anal fin with scattered dark pigments bordering fin rays, more concentrated along its proximal and distal length, resulting in a somewhat clearer medial area in few individuals. Adipose fin with scattered dark chromatophores along its area, except for its distal one third, which is hyaline. Paired fins hyaline with scattered dark pigments, more concentrated on intermembranes of unbranched ray. Midregion of both caudal-fin lobes with a field of dark chromatophores. Tips and base of both lobes of caudal fin hyaline (fig.1).

Distribution. Known only from tributaries of the río Portuguesa, río Orinoco drainage, Venezuela (fig. 5).

Etymology. The specific epithet otrynus is from the Greek meaning spur, in reference to the two very large spur-like hooks (processes of last unbranched and first branched anal-fin rays).

Comments. According to Ellis (in Eigenmann, 1918), Hyphessobrycon is distinguished from Hemigrammus only by presenting a naked caudal fin in opposition of the scaled caudal fin in the last genus. However, Weitzman (1977) affirmed that these genera cannot be distinguished either phylogentically or typologically as separate taxa because, as Böhlke (1955) pointed out, there are species which are intermediate in their caudalfin squamation. Even so, this author recognized his new species as belonging to Hyphessobrycon rather than Hemigrammus , employing a practical, typological procedure (amount of caudal-fin squamation), and based on the traditional definitions of these genera provided by Ellis (in Eigenmann, 1918). Hyphessobrycon otrynus shares with H. diancistrus the identical color pattern and the presence of two large hooks on each side of the caudal fin, which are indicative of a close relationship. Thus, we follow Weitzman (1977) in recognizing this new species in the genus Hyphessobrycon , emphasizing the putatively close relationship between these species.

Weitzman (1977) discussed that large anal-fin hooks are known in other species of Hyphessobrycon and Hemigrammus and cited Hemigrammus occelifer as an example, but emphasized that its unique and fairly large hook on each side of the anal fin, along with the several morphometric and meristic differences, indicate that there is no phylogenetic or typological proximity between H. occelifer and his H. diancistrus . Moenkhausia ceros Eigenmann (1908) was described as having the third anal-fin ray of males provided with a large retrorse hooks on each side. Examination of the holotype of M. ceros confirmed that this species can be promptly distinguished from H. otrynus by presenting a single developed bony hook on each side of the anal fin (vs. two large bony hooks), by presenting a complete lateral line (vs. incomplete), and by a distinct caudal-fin color pattern, with the middle rays of caudal fin black pigmented instead of the black blotched caudal-fin lobes, as observed in the latter species.

The occurrence of two large anal-fin hooks was discussed by Weitzman (1977) as being restricted to Tyttobrycon hamatus and Hyphessobrycon diancistrus . Notwithstanding this comment, this author enumerated several distinguishing features between these species and stated that sharing anal-fin hooks is most likely a case of convergence.

Hyphessobrycon otrynus displays a reduction to the number of the two anterior unbranched plus eight branched dorsal-fin rays, considering that the usual characid dorsal-finray count is two anterior unbranched rays plus nine branched rays ( Malabarba & Weitzman, 2003). The presence of two branched plus eight unbranched dorsal-fin rays is only scarcely distributed among individuals of a few species of Hyphessobrycon (e.g. Hyphessobrycon eilyos ). Malabarba & Weitzman (2003) hypothesized that eight branched dorsal-fin rays and four teeth in the inner row of the premaxillary bones are synapomorphies for a group of characids that they termed Clade A. This clade is formed by the subfamily Glandulocaudinae and the genera Cyanocharax , Attonitus , Boehlkea , Bryconacidnus , Bryconamericus , Caiapobrycon , Ceratobranchia , Creagrutus , Hemibrycon , Hypobrycon , Knodus , Microgenys , Monotocheirodon , Odontostoechus , Othonocheirodus , Piabarchus , Piabina, Rhynobrycon , and Rhinopetitia . Comparisons with representative species of Clade A revealed no further similarities among these species and H. otrynus , and the common presence of only eight branched dorsal-fin rays is most likely homoplastic, possibly indicating the paedomorphic nature of this reduction in H. otrynus .

Comparative material examined. Bryconamericus straemineus , LBP 4978, Creagrutus varii , LIRP 4342, holotype. Hemigrammus marginatus , LBP 268. Hyphessobrycon diancistrus , MZUSP 13179, paratype, Moenkhausia ceros , MCZ 49161, holotype. Piabina argentea LBP3886.

Figures

FIGURE 1. Hyphessobrycon otrynus, USNM 349418, holotype, 30.1 mm SL, Venezuela, Portuguesa, río Portuguesa.

FIGURE 2. Hyphessobrycon otrynus, LIRP 6040, paratype, 24.2 mm SL, premaxillary, maxillary and dentary; left side, lateral view (maxillary and dentary) or frontal view (premaxillary). Scale bar = 1 mm.

FIGURE 3. Radiograph of Hyphessobrycon otrynus, USNM 349418, holotype, 30.1 mm SL, Venezuela, Portuguesa, río Portuguesa.

FIGURE 4. Hyphessobrycon otrynus, LIRP 6040, paratype, 24.2 mm SL,. Partial view of anterior anal-fin rays showing the two large hooks on the last unbranched and first branched anal-fin rays, and the small hooks on the first to third branched anal-fin rays. Right side, lateral view. Scale bar = 1 mm.

Tables

TABLE 1. Morphometric data for Hyphessobrycon otrynus, new species.

	holotype	N	paratypes
			limits	mean
Standard length (mm)	30.1	11	22.4–29.4	24.5
Percentage of standard length
Greatest depth	29.8	11	28.8–33.8	31.6
Snout to dorsal-fin origin	52.2	11	49.8–54.8	52.5
Snout to pectoral-fin origin	29.6	11	26.7–31.8	30.2
Snout to pelvic-fin origin	45.7	0 9	44.7–50.4	47.7
Snout to anal-fin origin	64.0	11	63.1–66.4	64.9
Caudal peduncle depth	10.7	11	9.4–10.7	10.1
Caudal peduncle length	12.1	11	11.7–12.9	12.4
Pectoral-fin length	22.9	10	22.0–25.2	23.2
Pelvic-fin length	20.9	10	17.6–21.5	19.8
Dorsal-fin length	26.8	10	20.0–28.8	27.0
Dorsal-fin base	15.0	11	12.2–15.6	14.4
Anal-fin length	20.2	10	18.0–20.2	19.9
Anal-fin base	26.1	11	24.5–28.5	26.7
Eye to dorsal-fin origin	38.9	0 9	38.1–39.7	39.1
Dorsal-fin origin to caudal-fin origin	51.7	0 9	48.8–52.8	50.9
Head length	26.5	11	26.3–29.1	28.0
Head depth	16.7	11	16.6–19.6	18.3