A new species of Charax ( Ostariophysi , Characiformes , Characidae ) from northeastern Brazil

Charax awa sp. n. is herein described from the Rio Mearim, Rio Munim and Rio Turiaçu basins, three coastal river basins of northeastern Brazil located between the Rios Gurupi and Parnaíba basins. These have a complex and still poorly known biogeographic history. This region is ecologically extremely relevant since it comprises three of the main Brazilian biomes, as well as, transition zones between them: Amazônia, Brazilian Cerrado and Caatinga. Therefore, this area has faunal and floristic representatives of these three biomes, which makes it particularly relevant in terms of ecology, biodiversity and conservation. Charax awa sp. n. possesses a relatively small orbital diameter (22.1–28.5 % HL), what distinguishes it from most of its congeners, except from C. notulatus and C. caudimaculatus. It differs from C. caudimaculatus by a longer snout, and from C. notulatus by the number of scales around the caudal peduncle, as well as by the number of vertebrae. The new species herein described differs from its geographically closely distributed congeners, C. leticiae, C. niger, and C. pauciradiatus mainly by the relative horizontal orbital diameter. It is a “small-eyed” species. In addition, C. awa sp. n. can be distinguished from C. leticiae by having a maxilla extending to the vertical line posterior to the pupil, near the posterior orbital margin and by having a lower humeral spot distance. It can be distinguished from C. pauciradiatus by more scale rows from the pelvic-fin origin to the lateral line and more scale rows from the dorsal-fin origin to the lateral line and it differs from C. niger by having more transverse scale rows in space from the humeral spot to the supracleithrum. In addition, it differs from C. pauciradiatus and C. niger by the absence of bony hooks on anal and pelvic-fins rays of adult males.


Introduction
Characidae is the most species-rich family of Characiformes, comprising about 165 genera and more than 1.150 species, distributed along the river systems between southwestern Texas and Mexico in North America and Patagonia in South America (Nelson et al. 2016;Eschmeyer et al. smaller isolated river basins draining the Guiana Shield, and in the Lagoa dos Patos system, and other coastal lagoons of southern Brazil (Menezes and Lucena 2014).
The distribution of the genus is mainly concentrated in central and northern South America; there is no record for eastern Brazil and none of the valid species was assigned for the coastal river basins of northeastern Brazil by the recent taxonomic revision of the genus (see Menezes and Lucena 2014).However, some records of Charax for the coastal river basins of northeastern Brazil were made before the taxonomic revision made by Menezes and Lucena (2014): Martins and Oliveira (2011) recorded C. gibbosus for the Rio Mearim basin; Barros et al. (2011) recorded Charax sp. for the Rio Itapecuru basin; Martins and Oliveira (2011) recorded Charax sp. for the Rio Pericumã basin and Rio Mearim basin.
Charax can be distinguished from all other characid genera by the presence of a deep concavity on the latero-ventral portion of the cleithrum originating a relatively long posterior spiniform projection extending below pectoral-fin base; and an anterior shorter process oriented straight forward or either inclined or bent laterally (Lucena 1987, Mattox and Toledo-Piza 2012: fig 34, Menezes and Lucena 2014).A new species of Charax is herein described from the Rio Mearim, Rio Munim and Rio Turiaçu basins, three coastal river basins of northeastern Brazil.

Material and methods
Counts and measurements were taken according to Fink and Weitzman (1974), Menezes and Weitzman (1990) and Menezes and Lucena (2014), on the left side of specimens whenever possible, using a dig ital caliper with precision of 0.01 mm.Measurements are given as a percentage of standard length (SL), except for subunits of the head, which are given as a percentage of head length (HL).Vertebrae of the Weberian apparatus were not included in the vertebral counts, whereas the fused PU1+U1 of the caudal region was counted as a single element.Counts for supraneurals, vertebrae, rib pairs, branchiostegal rays, gill-rakers, premaxillary, maxillary, and dentary teeth, procurrent caudal-fin rays, and pterygiophores were taken only from cleared and stained paratypes (C&S), prepared according to Taylor and Van Dyke (1985); number of examined specimens are in parentheses.Osteological nomenclature follows Weitzman (1962).Diagnosis was made based on a unique combination of character states, according to Davis and Nixon (1992).Information about congeners was based on both comparative material and literature (e.g Lucena 1987, Mattox and Toledo-Piza 2012, Menezes and Lucena 2014)
Color in alcohol (Fig. 1A).Body pale yellow to light yellow, slightly darker dorsally.Both extreme dorsal and ventral regions of trunk with scattered dark chromatophores.Inconspicuous approximately rounded or slightly elliptical dark brown humeral blotch, extending about three to four scales horizontally and about five vertically.Dorsal part of head, snout, circumorbital region and opercle darker than rest of head.Scattered dark chromatophores on tip of snout and suborbital region.V-shaped lines of chromatophores over myosepta along epaxial and hypaxial muscles, more visible on mid-posterior portion of body.Inconspicuous, approximately triangular shaped dark blotch on caudal-fin base, with posterior dark chromatophores.Inconspicuous clear stripe at anal-fin base.All fins hyaline, or light brown at base, with scattered dark chromatophores more visible on interradial membranes.Anterior portion of first to third unbranched rays of dorsal and first unbranched rays of pectoral and pelvic-fin rays darker than remaining rays.
Color in life (Fig. 1B).Color pattern in life similar to coloration of preserved specimens.Body silver on, anterior portion, and silver to hyaline on posterior portion.
Anterior and dorsal portions of trunk darker, and sides of head darker than rest of body.Humeral and caudal-fin base blotches inconspicuous.Dorsal margin of trunk with conspicuous dark brown chromatophores.Purple longitudinal stripe along mid-portion of flank, extending posteriorly to anterior margin of caudal-fin base.Fins hyaline, with scattered dark brown or black chromatophores, more visible on interradial membranes.

Sexual dimorphism.
No apparent sexual dimorphism.
Distribution.Charax awa is known from the Rio Mearim, Rio Munim and Rio Turiaçu basins, Maranhão state, northeastern Brazil (Fig. 3).In addition, new species herein described differs from C. gibbosus, a species incorrectly identified for the same area of C. awa sp.n. by the following features:

Remarks
Charax awa sp.n. possesses a toothless ectopterygoid, absence of bony hooks on anal-fin rays of mature males, 8-10 transverse scales rows between the humeral spot and the suprecleithrum and 49-68 predorsal scales; while C. gibbosus has teeth on ectopterygoid, bony hooks on anal-fin rays of mature males, 5-6 transverse scales rows between the humeral spot and the suprecleithrum, and 38-45 predorsal scales.
Etymology.The specific epithet honors the term Awá, from Tupi-guarani, meaning "man, people, person", used by the native tribe Guajá, from the Maranhão state, for their self-denomination.

Discussion
Several authors have pointed out that Charax constitutes a monophyletic genus within the Characinae (Lucena 1987;Mirande 2010;Mattox and Toledo-Piza 2012;Menezes and Lucena 2014).The sister-group relationship between Charax and Roeboides was suggested by several authors (Lucena 1998(Lucena , 2000;;Mirande 2009Mirande , 2010;;Mattox and Toledo-Piza 2012).However, Oliveira et al. (2011) alternatively suggested a different relationship between these two genera, proposing that Charax is the sister group of the clade comprising Roeboides Günther, 1864 and Cynopotamus Valenciennes, 1850.The presence of (1) a well-developed notch on the latero-ventral portion of cleithrum originating a relatively long posterior spiniform projection extending below pectoral-fin base and (2) an anterior shorter process oriented straight forward, or either inclined or bent laterally, was proposed by Lucena (1987) as the synapomorphies of the genus, a hypothesis corroborated by Mattox and Toledo-Piza (2012) and confirmed in the new species herein described (Fig. 5).
Charax awa sp.n. possesses a relatively small eye or orbital diameter when compared to the other congeners, except C. notulatus and C. caudimaculatus (22.1-28.5 % HL; 26.1-28.5 % HL on specimens below 80 mm SL; and 22.1-25.4% HL on specimens above 80 mm SL; see Tables 1 and 2).Despite the larger specimens of C. awa sp.n. usually have a tendency to have smaller eye diameters when compared to the smaller specimens, the combined range of the eye diameter of these two size categories is even useful for the discrimination of the new species of all the congeners which possess a relatively larger eye diameter (29.6- 38.4 % HL combined).It is important to emphasize that the eye or orbital diameter is the main diagnostic character of Charax according to Menezes and Lucena (2014), which had used this character on their identification key to species of Charax, and as the first diagnostic feature in most of the species diagnoses.Other characters widely used by the last taxonomic revision of the genus were the lateral line, different types of scale counts, and the absence or presence or the number of teeth on the ectopterygoid.We confirmed here these characters as useful for species discrimination and taxonomy of the genus.
According to Menezes and Lucena (2014) a sexual dimorphism characterized by the presence of bony hooks on the anal and pelvic-fin rays of adult males is only recorded for C. pauciradiatus, C. michaeli, C. gibbosus and C. niger (in the case of the latter two, only in the analfin rays).Therefore, they concluded that the absence of these bony hooks is predominant across Charax.Charax awa sp.n. apparently exhibits this general pattern of the genus, since bony hooks on these fins were not recorded in any of our examined material of the species, including 220 specimens over 84.0 mm SL.Thus, the species apparently does not possess an evident sexual dimorphism.
by the possession of a longer snout; from C. notulatusLucena, 1987 by the number of scales around the caudal peduncle(15-18 vs. 20-22)  and by having more vertebrae(35 vs. 32).Furthermore, Charax awa sp.n. can be distinguished from C. condei, C. hemigrammus and C. stenopterus by having the lateral line complete (vs.incomplete); from C. delimai, C. metae and C. tectifer by having a toothless ectopterygoid (vs.presence of teeth on ectopterygoid) and having the anal-fin origin always anterior to the vertical through the dorsal-fin origin (vs.anal-fin origin on, or slightly posterior to the vertical through the dorsal-fin origin); from C. condei, C. delimai, C. hemigrammus, C. metae, C. pauciradiatus and C. stenopterus by the number of scale rows from the pelvic-fin origin to the lateral line (11-12 vs. 6-10 combined); from C. pauciradiatus by having more scale rows from the dorsal-fin origin to the lateral line (15-18 vs. 13-14).It can be distinguished from C. niger by having 8-10 transverse scale rows in space from the humeral spot to the supracleithrum (vs.5-6); from C. condei, C. delimai, C. metae, C. rupununi Eigenmann, 1912 by the number of scale rows around the caudal peduncle(15-18 in C. awa sp.n. vs. 12-14 combined in C. condei  and C. rupununi, 19-21 combined in C. delimai and C. metae).Finally, it differs from C. leticiae by having the maxilla extending to a vertical line posterior to pupil, near the posterior orbital margin (vs.maxilla extending slightly beyond vertical through middle of pupil) and from humeral spot distance (35.8-38.0% SL vs. 39.0-44.0% SL).

.
The new species herein described differs from its geographically closely distributed congeners, C. leticiae, C. niger, and C. pauciradiatus, with records in the Lower Amazon, Capim, upper Itapecuru and Tocantins river basins (Fig.4), mainly by the horizontal orbital diameter (see diagnosis section).In addition, C. awa sp.n. can be distinguished from C. leticiae by having the maxilla extending to a vertical line posterior to pupil, near posterior orbital margin while C. leticiae shows the maxilla extending slightly beyond vertical through middle of pupil and by humeral spot distance (32.1-38.0% SL vs. 39.0-44.0% SL).It can be distinguished from C. pauciradiatus by possessing 11-12 scale rows from the pelvic-fin origin to the lateral line and 15-18 scale rows from the dorsal-fin origin to the lateral line, while C. pauciradiatus possess 6-10 and 13-14, respectively, and differs from C. niger by having 8-10 transverse scale rows in space from the humeral spot to the supracleithrum, while C. niger possess 5-6.Moreover, it differs from C. pauciradiatus and C. niger by the absence of bony hooks on anal and pelvic-fins rays of adult males.This last character is emphasized in the discussion section.

Figure 4 .
Figure 4. Distribution of Charax awa sp.n., C. leticiae, C. pauciradiatus and C. niger.Charax awa sp.n. (red circle), C. leticiae (yellow circle), C. pauciradiatus (black circle) and C. niger (white circle).The type localities of the species are marked with an asterisk.Information of this map was based on our examined material and data provided by Lucena 1987, and Menezes and Lucena 2014 .See Suppl.material 1.

Table 2 .
Morphometric data related to the horizontal eye diameter of Charax awa presented in separate classes of standard length.