A new species of Bryconops ( Ostariophysi : Characiformes : Characidae ) from the upper rio Tocantins drainage , Brazil

A new species of the genus Bryconops, subgenus Bryconops, is described from the rio Conceição, a tributary to the rio Palma, upper rio Tocantins drainage, Tocantins State, Brazil. The new species is distinguished from all its congeners, except B. humeralis and B. vibex by the color pattern in vivo (dorsal, adipose, and caudal fins entirely orange). The new species is easily distinguished from B. humeralis and B. vibex by the absence of a humeral spot and by the lack of maxillary teeth (vs. presence of a single humeral spot and presence of 1-3 maxillary teeth on both sides). Furthermore, the new species is distinguished from B. vibex by the number of perforated lateral line scales (38-41 vs. 44-46).


Introduction
Bryconops Kner, a genus of the characiform family Characidae, comprises 20 valid species of small characids distributed across a major portion of South America through the Orinoco, Amazon, Tocantins-Araguaia, Paraná-Paraguay, and São Francisco river basins to many of the smaller river systems of the Atlantic versant from the Essequibo to Oyapock (Lima et al., 2003;Chernoff & Machado-Allison, 2005;Wingert & Malabarba, 2011;Silva-Oliveira et al., 2015).Bryconops is presumably a monophyletic genus diagnosed by synapomorphies related to the anatomy of cephalic sensory system and shape of the maxillary bone (Chernoff & Machado-Allison (1999).The species of genus Bryconops were divided into two putative monophyletic subgenera, i.e.Bryconops and Creatochanes Günther, based on synapomorphies related to the maxillary bone, gill rakers, and infraorbitals (Chernoff & Machado-Allison, 1999, 2005).
Recent ichthyofaunal surveys throughout the upper portion of rio Tocantins drainage yielded samples of a new species of the subgenus Bryconops.This paper intends to formally describe this new species.

Material and Methods
Examined specimens belong to the following fish collections: Academy of Natural Sciences, Philadelphia (ANSP); Laboratório de Ictiologia Sistemática, Universidade Federal do Tocantins, Porto Nacional (UNT); Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre (MCP); Museu de Zoologia da Universidade de São Paulo, São Paulo (MZUSP); Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro (MNRJ); Naturhistorisches Museum, Wien (NMW); and University of Michigan Museum of Zoology, Ann Arbor (UMMZ).Comparisons to species not listed in comparative material were based on the literature.Measurements from specimens were taken with vernier calipers to nearest tenth of millimeter under a stereomicroscope.Measurements were taken between the landmarks established by Sidlauskas et al. (2006: fig.2), except for the exclusion of landmark 4 and the displacement of landmark 5 to the adipose-fin terminus.An additional measurement, interorbital width, was included, following Fink & Weitzman (1974).Measurements other than standard length (SL), were expressed as percents of SL, except for subunits of the head, which are expressed as percents of head length (HL).Measurements were made on the left side of specimens, whenever possible.Counts follow Fink & Weitzman (1974), except for the inclusion of: (i) number of longitudinal rows of scales from the first scale ventral to the lateral line to pelvic-fin insertion; (ii) number of non-perforated scales on lateral line; and (iii) principal rays of caudal-fin.In the description section, the numbers in parentheses after each count represent the frequency of that count and asterisks indicate counts of the holotype.Some specimens were cleared and stained (c&s) according to the procedures described in Taylor & Van Dyke (1985).Counts of teeth (except maxillary teeth) and tooth cusps, gill rakers on the first gill arch, vertebrae, supraneurals, and procurrent caudal-fin rays were obtained only from c&s specimens.The number of maxillary teeth was counted either on c&s or alcohol specimens.Vertebrae of the Weberian apparatus were counted as four elements (as in Fink & Weitzman, 1974), and the compound caudal centrum (PU1 + U1) was counted as one vertebral element (Lundberg & Baskin, 1969).Patterns of circuli and radii were defined based on two scales located on the vertical through dorsal-fin origin; the first one being a scale from the lateral line and the second a scale immediately above it.Paratypes.Brazil. Tocantins. MCP 49200, 24, 32.0-64.5 mm SL, MNRJ 44220, 20, 28.8-62.0 mm SL;MZUSP 118553, 11, 30.8-38.9 mm SL, and UNT 12791, 45 (14 c&s), 27.4-65.0mm SL, collected with the holotype.MZUSP 114466, 10, 21.5-48.3(38-41 vs. 9-23, 30, 31-36, 43-46, 43-47, 43-48, 44-46, 45-46, 54, and (20-25 vs. 28-29).Bryconops tocantinensis is distinguished from B. caudomaculatus (Günther) by the horizontal eye diameter (12.3-14.4% SL vs. 9.0-12.0%SL), and by the number of scale rows around caudal peduncle (16 vs. 12-14).

Bryconops tocantinensis, new species
Description.Morphometric data presented in Table 1.Moderate to small-sized species of Bryconops, largest specimen examined 65.0 mm SL.Elongate body, laterally compressed.Greatest body depth at dorsal-fin origin.Dorsal body profile convex from snout to vertical through anterior nostrils; straight or slightly convex from posterior nostrils to tip of supraoccipital bone; convex from this point to dorsal-fin origin.Straight and posteroventrallyaligned along dorsal-fin base; postdorsal profile straight from base of last dorsal-fin ray to adipose-fin origin and concave from latter point to end of caudal peduncle.Ventral profile convex from snout to pelvic-fin insertion; straight or slightly convex from this point to anal-fin origin; straight and posterodorsally-aligned along anal-fin base; postventral profile concave from base of last anal-fin ray to end of caudal peduncle.
Head large.Posterior margin of opercle slightly sinusoidal.Mouth terminal.Premaxilla and dentary positioned at same level, or premaxilla slightly longer than dentary.Snout shorter than eye diameter.Eyes large.Adipose ocular membrane well-developed.Maxilla moderately enlarged, its distal portion not reaching articulation between second and third infraorbitals, and not reaching vertical through middle of orbit.Anteroventral margin of maxilla describing a semicircle just ventral to ascending process.Second and third infraorbitals articulating only dorsally, leaving a naked area in their ventral margins; third infraorbital moderately developed, not reaching preopercle ventrally or at its angle.Antorbital present, bearing well-developed infraorbital sensory canal.Supraorbital bone present, contacting antorbital anteriorly, not reaching sixth infraorbital posteriorly.Six infraorbital bones (Fig. 2).Branching of laterosensory canal of fourth infraorbital present (see Mirande, 2010: 407;fig. 39).
Color in alcohol.Males and females with same color pattern.Overall ground coloration of body dark yellow to slightly brown.Dorsum of head, snout, lower lip and anterior portion of maxilla dark brown.Infraorbitals silvery white.Gular area and posterior portion of maxilla yellowish or whitish.Dentary with frontal portion blackish and ventral portion yellowish.Orbit whitish with dark pupil.Dorsal profile between tip of supraoccipital bone and insertion of uppermost caudalfin ray dark.Dorsolateral scales with reticulated pattern due to higher concentration of melanophores at their distal borders.Dark brown midlateral stripe narrow anteriorly and progressively expanding from head to under dorsal fin; then becoming slightly narrower towards middle caudal peduncle; and then broadening on distal portion of caudal peduncle, merging to diffuse, oblong darkened caudal spot.Midlateral stripe reaching greatest depth at vertical through end of dorsal-fin base, occupying 2 or 2.5 scales rows wide above lateral line.Presence of darker line on midlateral stripe, most evident between vertical through dorsal-fin origin and vertical through base of last branched anal-fin ray.Ventral portion of body below midlateral stripe yellowish, with many chromatophores scattered between anal-fin base and midlateral stripe.Humeral spot absent.Pores on lateral line being readily visible up to at least vertical through dorsal-fin origin.Dorsal fin hyaline with dark chromatophores along rays.Adipose fin hyaline, without dark chromatophores.Well-developed ocellus on base of upper lobe of caudal fin.Clear area on base of lower lobe of caudal fin without ocellus.Distal portions of upper and lower lobes of caudal fin dark on white background.Middle caudal-fin rays slightly dark.Pectoral and pelvic fins hyaline with few dark chromatophores along rays.Anal fin hyaline with few dark chromatophores on tip of first four rays.Geographic distribution.Bryconops tocantinensis is known from its type locality, rio Conceição, a tributary to the rio Palma, upper rio Tocantins drainage, Tocantins, Brazil (Fig. 5).Etymology.The specific name, tocantinensis, is an adjective and refers to the rio Tocantins drainage, where this species is currently known to occur.

Remarks. The predominant condition of maxilla in
Bryconops tocantinensis is edentulous.However, among the fifty-two specimens examined, only one specimen exhibited two conical teeth on the left maxilla and additional one exhibited just one conical tooth on the same side.
Conservation status.Considering that, although its known geographic distribution is restricted, current relevant threats to the species were not detected in its distribution area, Bryconops tocantinensis could be classified as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2016).Further studies on biology, ecology and distribution of the species could detect plausible threats to the population of Bryconops tocantinensis, perhaps leading to a revaluation of the conservation status of the species.

Discussion
Two character states exhibited by Bryconops tocantinensis allow its recognition as a member of the genus Bryconops, namely: (1) the presence of a welldeveloped infraorbital sensory canal on the antorbital, and (2) supraorbital sensory canal extending onto nuchal scales.These conditions were employed by Chernoff & Machado-Allison (1999: 359) to diagnose the genus Bryconops.
Chernoff & Machado-Allison (1999) also proposed a third character as diagnostic for the genus Bryconops: the ventral edge of maxilla curving sharply posteriorly, almost 90°, its tip extending to or beyond the quadrate socket of the articular.However, in Bryconops tocantinensis the distal tip of maxilla does not reach the quadrate socket of the articular.Moreover, the condition exhibited by B. tocantinensis is shared with other species of the genus (e.g., B. disruptus and B. inpai).This situation evinces the need of reviewing the diagnosis of the genus.Also, a cladistic diagnosis encompassing all species of the genus Bryconops is still wanting.However, this issue is beyond the goals of this paper and should be deferred to a taxonomic review of the genus coupled with a phylogenetic study.
Moreover, Bryconops tocantinensis exhibits reduction in the ossification and denticulation of the gill rakers, and usually lacks maxillary teeth (see Remarks).Such features allow its recognition as a member of the subgenus Bryconops sensu Chernoff & Machado-Allison (2005: 5).
Although some authors reported the presence of Bryconops species in the rio Tocantins (e.g., Lucinda et al., 2007;Lima & Caires 2011), Bryconops tocantinensis is the first species of Bryconops described from the rio Tocantins drainage and may be an additional example of exclusive fish species from its upper and middle portion, which is recognized by several authors as an area of endemism for several Neotropical freshwater fish groups (e.g., Cardoso & Lucinda, 2003;Bertaco & Carvalho, 2010;Bertaco et al., 2011aBertaco et al., , 2011b)).