Hemigrammus tocantinsi: a new species from the upper rio Tocantins basin, Central Brazil (Characiformes: Characidae)

Hemigrammus tocantinsi is described from the upper rio Tocantins basin, Chapada dos Veadeiros, Goiás State, Central Brazil. The new species differs from its congeners by the presence of 15-17 branched anal-fin rays, longitudinal stripe relatively narrow anteriorly and wider posteriorly, and one or two maxillary teeth. Sexual dimorphism of the new species is characterized by differences among the color in life, adipose-fin origin, body measurements, in addition to presence of bony hooks in the anal and pelvic fins of males.


Introduction
Hemigrammus Gill is a group which houses small characids fishes, and includes 51 valid species widespread throughout South American river drainages from Orinoco to Paraguay-Paraná river basins (Lima et al., 2003;Bertaco & Carvalho, 2005;Marinho et al., 2008;Lima & Sousa, 2009).None of the diagnostic characters presently used to recognize Hemigrammus are unique to the genus, e. g., premaxillary teeth in two rows, five or more teeth on the inner premaxillary row, incomplete lateral line, and caudal fin scaled.Eigenmann (1918) is still the most complete taxonomic review of Hemigrammus to date, and Géry (1977) made the last survey on the genus.Those authors recognized species groups based mainly on similarities of color pattern.No hypothesis of intrageneric relationships of Hemigrammus is available at the moment and the genus is non-monophyletic according to Mirande (2009), who assigned the genus to his Hemigrammus clade based on his weighed analysis, although not presenting any synapomorphy for the group.
The discovery of the new species was done during recent collections in rivers and streams from the upper rio Tocantins basin, in the Chapada dos Veadeiros region.The species herein described is treated as Hemigrammus since it better conforms to the Eigenmann's definition and represents the first species of the genus described to the rios Tocantins-Araguaia basin.

Material and Methods
Counts and measurements follow Fink & Weitzman (1974) and Lima & Moreira (2003), with the exclusion of the distance of snout to pectoral-fin origin, and the addition of the dorsalfin origin to adipose-fin origin, and head depth, which was measured at vertical through the posterior end of supraoccipital spine.Measurements were made with a caliper rule to the nearest 0.05 mm on the left side of the specimen whenever possible, and presented as percents of standard length (SL) or head length (HL).In the description, counts are followed by their frequency in parentheses, and an asterisk indicates the count of the holotype.In the list of paratypes and comparative material examined, the total number of specimens in the lot is followed by the number of those examined (in parentheses), cleared and stained (c&s) individuals (if any), and SL of all specimens analyzed.Counts of vertebrae, supraneurals, gill-rakers of the first arch, branchiostegal rays, procurrent caudal-fin rays, and small dentary teeth were taken from five c&s specimens prepared according to Taylor & van Dyke (1985).Vertebral counts include the four vertebrae in the Weberian apparatus and the fused PU1+U1 of the caudal region as a single element.Pattern of circuli and radii was defined on scales sampled from the region between the lateral line and the insertion of pelvic-fin.Comparisons and data of species not available for examination were taken from the literature.
Description.Morphometric data summarized in Table 1.Body compressed, moderately short, greatest body depth at vertical through dorsal-fin origin.Dorsal profile of head convex from tip of upper jaw to vertical through anterior nostril; slightly straight or convex from that point to tip of supraoccipital spine.Dorsal profile of body slightly convex from posterior tip of supraoccipital spine to base of last dorsal-fin ray, and straight to adipose-fin origin.Ventral profile of body convex from tip of lower jaw to pelvic-fin origin, straight or slightly convex from that point to anal-fin origin, and straight and posterodorsally slanted along anal-fin base.Dorsal and ventral profile of caudal peduncle approximately straight.Eyes large, without distinct adipose eyelid.Jaw isognathous, mouth terminal.Maxilla extending posteriorly surpassing vertical through anterior margin of eye, aligned approximately at 45 degree angle relative to longitudinal axis of body.Nostrils close to each other, anterior opening smaller and circular, posterior one twice larger and oval.Median frontoparietal fontanel extending from mesethmoid to supraoccipital spine.Infraorbital series complete, with fourth infraorbital reduced dorsally (triangular shape) or absent sometimes, allowing contact between third and fifth infraorbitals.Infraorbital laterosensory canal close to inferior orbital margin, extending from posterior half of first infraorbital up to sixth orbital.Third infraorbital largest, double size of the others (in length and depth), contacting the preopercle laterosensory canal ventrally and posteriorly.

Color in alcohol.
Overall body color varying from whitish to pale yellowish.Head dusk to dark brownish dorsally.Region from the posterior portion of second to fifth infraorbital and opercular apparatus silvery on specimens recently collected and yellowish on long time alcohol preservated ones.Small dark melanophores surrounding nare, lips, dorsal margin of maxillary bone, and anterior margin of orbit; larger melanophores scattered over infraorbitals three-six and opercular apparatus.Humeral region with concentration of melanophores occupying two scale rows above and one scale row bellow lateral line, resulting in faint humeral spot.Portion of spot above lateral line two scales wide and one scale wide bellow it.Dorsal and dorso-lateral portions of body with a reticulated pattern due to concentration of melanophores at the posterior margin of the scales.Lateral side of body with scattered melanophores, except at the abdominal region.
Longitudinal stripe dark, one-scale wide, and extending from vertical through dorsal-fin origin to caudal-peduncle end, extending onto proximal one-third of middle caudal-fin rays.Lower lateral side of caudal region with few melanophores following the muscles epaxialis and hypaxialis superficial lines.All fins hyaline with scattered melanophores, sometimes bordering the margins of the rays.Color in life.Overall body and head color pattern reddish in males and yellowish in females.Pattern of melanophores distribution on head, body and fins similar to that described for specimens in alcohol.Proximal two thirds of dorsal, pectoral, pelvic, anal and caudal-fin rays red-orange in males and yellowish in females, except middle caudal-fin rays.Proximal portion of adipose fin and ventral surface of body from the end of pelvic-fin insertion to lower caudal-fin rays origin orange to reddish in males and yellowish in females (Fig. 4) (see also Sexual dimorphism).
Sexual dimorphism.Bony hooks on pelvic and anal-fin ray were observed only in males larger than 23.9 mm SL.Pelvic fin of males bearing small bony hooks along ventromedial border of first to fifth branched rays; one hook per ray segment.Anal fin with small bony hooks situated on distal portion of anal-fin rays, from the last unbranched anal-fin ray to first to eighth branched rays; one hook per ray segment.Males and females also differ in proportions of the pectoral and pelvic fins (Fig. 5), dorsal-and anal-fin base length, and pelvic fin to anal fin distance (Table 1), and in the anal-fin distal border shape, which is approximately straight on males and slightly concave in the anterior portion in females.Adipose fin located immediately after vertical through last branched anal-fin ray insertions in females and at vertical through last three or four anal-fin ray insertions in males.Tip of longest ray reaching anal-fin origin in males but not in females.Live specimens, or just after fixation, possess body and fins red to orange on males and yellowish in females (Fig. 4).Gill glands (Burns & Weitzman, 1996) were not found on first gill arch on both males and females.
Etymology.The specific name tocantinsi is a reference to the rio Tocantins basin, where the new species inhabit.A noun in apposition.Table 1.Morphometric data for holotype and 58 paratypes of Hemigrammus tocantinsi from upper rio Tocantins basin.SD = standard deviation; m = male (n = 25, including holotype); f = female (n = 34).
Ecological notes.The new species lives in streams, occuring in semi-lentic and lotic shallow areas (up to 1 m deep) with riparian vegetation composed by trees and shrubs (Fig. 7).
The new species was collected syntopically with Aspidoras albater, Astyanax sp., Characidium stigmosum, Corumbataia veadeiros, and Trichomycterus sp.Stomach contents of five specimens (UFRGS 11300, 25.1-27.1 mm SL) were mainly composed by Diptera (pupae) and allochthonous insects, but it was also found authochthonous insects and digested vegetal matter in a lesser amount.
The classical definition of Hemigrammus differs from Hyphessobrycon only by the presence of scales over the caudal-fin lobes.Descriptions of Hemigrammus species usually only remark the presence of the caudal-fin scales, rarely describing their shape, size or distribution pattern.In fact, dealing with this character is not an easy task.The scales covering the caudal-fin lobes are feeble and easily lost by friction even on recent collected material.Finding an intact caudal fin with its scales at the original position is unusual on specimens from collections, and very unlikely on old type material.This lack of data obscures how much information the caudal-fin squamation could bring to elucidate the evolutionary history of the Hemigrammus and other Characidae species.Hemigrammus tocantinsi has scales covering one-third of the lower caudal lobe (Fig. 3a).The scales cover a smaller extension of the caudal-fin lobe than found in other Hemigrammus species, like H. marginatus (Fig. 3b), but larger than found on Hyphessobrycon species, what could raise some doubt about its generic position.A similar condition was also described by Böhlke (1955) for Hemigrammus mimus, considered by him as an "intermediate [state] between what Dr. Eigenmann referred to as 'caudal scaled' and 'caudal naked except at its base' ".Problems concerning variation on caudal-fin scale patterns were also observed in Bryconamericus and Knodus, where Knodus meridae, the type species of the genus, presents similar caudal-fin scale arrangement to Bryconamericus iheringii (see figs. 12 to 14 in Weitzman et al., 2005).As asserted by the former authors, probably the caudal-fin squamation has a complex evolutionary history, and the comparison of caudalfin scale patterns among species of Hemigrammus and Hyphessobrycon for phylogenetic purposes needs detailed ontogenetic study, as well as in Bryconamericus and Knodus.The new species herein described is designated to Hemigrammus at the moment and further discussion about its generic position depends on phylogenetic studies including the species.Detailed studies of squamation on caudal fin will possibly benefit the results.
When compared to Hyphessobrycon species, Hemigrammus tocantinsi would be assigned to "group d" of Géry (1977), which includes species with both humeral and caudal spots, and a longitudinal band or line along the body (such as H. tropis).The species from this group were updated by Carvalho et al. (2008), now with addition of H. hamatus