Astyanax elachylepis , a new characid fish from the rio Tocantins drainage , Brazil ( Teleostei : Characidae )

A new characid species, Astyanax elachylepis, is described from the rio Tocantins drainage. The new species is distinguished from its congeners by possessing 48-53 perforated scales along the lateral line, a large caudal-peduncle spot, the presence of bony hooks on dorsal, anal, pelvic, and pectoral fins of males, one or two vertically-elongated humeral spots, one maxillary tooth, and 22-27 branched anal-fin rays.


Introduction
The genus Astyanax Baird & Girard, 1854 is a speciose characid genus, including at least 86 valid species distributed from southern United States to central Argentina (Lima et al., 2003).Astyanax was first revised by Eigenmann (1921Eigenmann ( , 1927)), whose accounts still constitute the sole all-inclusive review of the genus.Most subsequent papers either involve the description of new species or are taxonomic reviews of species occurring in restricted geographic areas of South and Central America.The systematics of the genus is further complicated by the lack of evidence corroborating its monophyly (Weitzman & Malabarba, 1998).
The examination of Astyanax samples housed at the MCP and UNT collections allowed the discovery of an undescribed species of the genus from the rio Tocantins drainage.This paper intends to formally describe this new species.

Methods and materials
Counts and measurements followed Fink & Weitzman (1974), with the exception of the number of scale rows below lateral line, which were counted from the scale row ventral to lateral line to the scale row nearest the first pelvic-fin ray.Vertebral counts, supraneurals, gill-rakers of the first arch, and procurrent caudal-fin-ray counts were taken from two cleared and stained (c&s) paratypes were prepared according to Taylor & Van Dyke (1985).Teeth counts were taken in all type specimens.Vertebral counts include the four vertebra of the Weberian apparatus and the terminal centrum, counted as one vertebra.Lower and upper jaws of one c&s paratype prepared for SEM (scanning electronic microscopy).
Measurements were taken point to point with an electronic caliper on the left side of specimens whenever possible.All measurements other than standard length (SL) are expressed as a percents of SL except subunits of the head, which are expressed as a percents of head length (HL)  Description.Morphometric data summarized in Table 1.Body compressed and elongate; greatest body depth usually anterior to dorsal-fin origin.Dorsal head profile straight or slightly concave.Profile convex from supraocciptal tip to base of last dorsal-fin ray, and straight towards adipose-fin origin.Ventral profile of head convex.Ventral body profile slightly convex to nearly straight from pectoral-fin origin to pelvic-fin origin, and straight to slightly concave towards anal-fin origin.Body profile along anal-fin base posterodorsally slanted.Caudal peduncle elongate, nearly straight to slightly concave along dorsal and ventral margins.Snout rounded from margin of upper lip to vertical through anterior nostrils.Head small.Mouth terminal.Maxilla extending posteriorly to under center of orbit, and slightly curved aligned at angle of approximately 45 degrees to longitudinal body axis.Anterodorsal border of maxilla concave and posterodorsal border slightly convex.Anteroventral and posteroventral borders convex.Maxilla slightly widened posteriorly.
Two tooth rows on premaxilla.Outer row with three or four, tricuspid or pentacuspid teeth with central cusp longer.Inner row with five teeth, gradually decreasing in length from first to third teeth; last two smaller, with five to seven cusps, with central cusp twice or three times longer and broader than other cusps.Maxilla with one or two (usually one), tricuspid or pentacuspid teeth, with central cusp longer.Three or four anteriormost dentary teeth larger, with seven cusps, followed by one or two teeth of medium sized with five cusps, and six teeth with one to three cusps or conical; central cusp in all teeth two to three times longer and broader than other cusps.All cusp tips slightly curved towards inside of mouth (Fig. 3).
Dorsal-fin rays ii, 9 (n = 66); first unbranched ray approximately one-half length of second ray.Dorsal-fin origin located posterior to middle of SL and posterior to vertical through pelvic-fin origin.Dorsal-fin rays of males bearing one or two pairs of small retrorse bony hooks along posteroventral border of each lepidotrichia segment, usually between first and eighth branched rays, and located along posteriormost branch and on distal third length of each ray.Adipose-fin located approximately at vertical through insertion of base of 21 st -22 nd anal-fin rays.
Anal-fin rays ii-iv, 23-25 (rarely 22 or 26-27, mean = 24.2,n = 66).First unbranched ray visible only in c&s specimens.Anal-fin profile smoothly concave in females, and nearly straight in males.Anal-fin origin posterior to vertical through base of last dorsal-fin ray.Anal-fin rays of males bearing one

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pair of small, elongate, retrorse bony hooks along posterolateral border of each segment of lepidotrichia, usually along last unbranched ray and 20 th branched rays; hooks more numerous along second through seventh branched rays.Hooks usually located along posteriormost branch and distal half to two-thirds length of each ray.Pectoral-fin rays i, 11-15 (mean = 12.5, n = 66).Pectoral-fin tip not reaching pelvic-fin origin in males and females.Pectoral-fin rays of males similar to those present on dorsal-fin rays.Pelvic-fin rays i, 7 (n = 66).Pelvic-fin origin located anterior to vertical through dorsal-fin origin.Pelvic fin of males usually bearing one retrorse bony hook per lepidotrichia along ventromedial border of second to fourth branched rays.Hooks usually located along posteriormost branch and distal half to two-thirds length of each ray.Caudal-fin forked, with 19 principal rays.Dorsal procurrent rays 11-13 (n = 2).Ventral procurrent rays 10-11 (n = 2).
Color in alcohol.Dorsal and dorsolateral portion of head and body dark brown.Scales on lateral and ventral surface of body weakly pigmented.Two humeral spots; first black and narrow, large and vertically elongate, located over second to fourth lateral line scales and extending over five or six horizontal series of scales, including lateral line.Second humeral spot, dark and very diffuse, located on first series of scales above lateral line, between seventh to tenth series of scales and extending over two or three horizontal series of scales.Second humeral spot not visible in some specimens.Midlateral body with silvery stripe extending from humeral spot to caudal-peduncle.Large, horizontally elongate, black spot on caudal peduncle forming lozenge or square spot, and extending over middle caudal-fin rays.Remaining fins lacking distinctive patches of pigmentation (Fig. 2).Some specimens examined just some months after fixation in formalin (UNT 1891), yet presented dorsal, pelvic, anal and caudal fins red-orange pigmented.
Sexual dimorphism.Males of A. elachylepis are easily recognized by the presence of bony hooks on the dorsal-, anal-, pectoral-, and pelvic-fin rays (see Description).All males examined possess bony hooks along these fins (76.5-115.0mm SL).Males and females also slightly differ concerning pectoral and pelvic-fin lengths (Table 1) and anal-fin shape, which is concave in females and nearly straight in males.
Etymology.The name elachylepis is from Greek, elachis, small, short, little, plus lepís, meaning scales, alluding to the small size of scales.A noun in aposition.

Discussion
The new species is described in Astyanax according to the current definition of the genus, proposed by Eigenmann (1921Eigenmann ( , 1927)).Astyanax elachylepis possess very high lateralline scales counts, an uncommon feature among the species on the genus, and also exhibited by A. anterior, A. bourgeti, A. erythropterus, A. festae, A. integer, A. microlepis, A. pellegrini, and A. symmetricus.The new species differs from these, but A. microlepis, by a smaller number of branched anal-fin rays (22-27 vs 28-45).Astyanax elachylepis differs from A. microlepis, described from Piedra Moler [upper río Cauca, Colombia], by a larger number of branched anal-fin rays (22-27 vs 19-22), presence of a larger spot in the caudalpeduncle, and by the presence of bony hooks in dorsal-, anal-, pelvic-, and pectoral-fin rays in males.
Astyanax maximus Steindachner, 1877, described from Tullumayo and Monterico in Peru, possess color pattern and maximum length very similar to A. elachylepis.However, the examination of four syntypes of A. maximus (NMW 57662,57663 and 57664), revealed that all possess 39-40 lateral-line scales and 26-28 branched anal-fin rays.Five additional specimens of A. maximus (ANSP 136807 and 119875) were examined, which also exhibit 26-28 anal-fin rays and 38-41 lateralline scales.Given that these counts do not overlap the counts of the new species, and given the distance between the type Table 1.Morphometric data of holotype (H, male) and paratypes of Astyanax elachylepis from rio Tocantins drainage (n = 66 including the holotype).m, males (n = 18); f, females (n = 48).

Fig. 1 .
Fig. 1.Rio Tocantins drainage showing the collection localities of Astyanax elachylepis.Some symbols represent more than one lot or locality.T = type locality.