Hasemania piatan , a new characid species ( Characiformes : Characidae ) from headwaters of rio de Contas , Bahia , Brazil

Hasemania piatan is described from the upper rio de Contas drainage, Bahia, northeastern Brazil. It can be easily distinguished from its congeners by having 18 principal caudal-fin rays. The new species differs further from congeners by a combination of seven branched dorsal-fin rays, six branched pelvic-fin rays, anal-fin base not covered by scales, presence of only five infraorbitals, and presence of a humeral blotch. It also can be distinguished by having 10-13 branched anal-fin rays, 27-32 scales on longitudinal series, 10-12 circumpeduncular scales, and one to three maxillary teeth.


Introduction
Hasemania is a small characid genus restricted to rivers draining the Brazilian Shield.The genus was proposed by Ellis (1911) who defined it as "like a Hyphessobrycon, but without an adipose".Hasemania was thus originally characterized by the absence of an adipose fin, presence of two rows of premaxillary teeth, absence of maxillary teeth or with a few in its upper angle, lateral line incomplete, caudal fin naked, and pectoral fin frequently archaic in small specimens.The genus presently includes seven species: Hasemania nana (Lütken) from the rio São Francisco basin, H. melanura Ellis (type species) and H. maxillaris Ellis, both from the rio Iguaçu basin, H. hanseni (Fowler) from Goiás (precise locality unknown), H. crenuchoides Zarske & Géry from upper rio Paraná basin, H. nambiquara Bertaco & Malabarba from upper rio Tapajós basin, and H. kalunga Bertaco & Carvalho from upper Tocantins basin.Ongoing taxonomic and phylogenetic studies of Hasemania by one of us (JPS) will possibly result in a redefinition of the genus and rearrangement of the number of its species.
A recent expedition to headwaters of rio de Contas, an area poorly known ichthyologically and representing the highest point on northeastern Brazil (around 1.300 m a.s.l.), revealed a small characid, distinguishable by a series of morphological and meristic characters.We herein describe this new distinctive characid in Hasemania according to Ellis' definition.

Material and Methods
Counts and measurements were taken according to Fink & Weitzman (1974) and Menezes & Weitzman (1990), except for horizontal scale rows below lateral line which are counted to the pelvic-fin insertion.Upper scales count of transverse series represents the number of rows of scales between median dorsal row and the lateral line, not including the median dorsal row or the small scale just below dorsal-fin rays insertion.The half scale between the lateral line and pelvic fin was only counted when more than half scale is above pelvic fin origin.In the description, the frequency of each count is given in parentheses after the respective count.An asterisk indicates counts of the holotype.Vertebrae, supraneurals, procurrent caudal-fin rays, branchiostegal rays, gill-rakers, and dentary teeth counts and cusp numbers were taken only from cleared and stained paratypes (c&s), prepared according to Taylor & van Dyke (1985).Vertebrae of the Weberian apparatus were counted as four elements, included in the vertebral counts, 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 dorsal-fin.In the material listed, the total number of specimens and its size range comes first, followed by the number and size range of measured specimens (in parentheses), if different.Institutional abbreviations follow Ferraris (2007) 21), or 3(1) teeth bearing one to three cusps.Dentary with four or five larger teeth anteriorly, with three to five cusps, followed by four or five distinctly smaller conical ones (5); anteriormost teeth usually with three cusps, except in largest specimen with five cusps (Fig. 3).

Color in life.
Freshly collected specimens had overall coloration tan, with yellowish ventral portion of body (Fig. 2).Silvery hue present over some scales, major portion of iris, posterior infraorbitals, preopercle, and opercle.Dorsal portion of iris darkened.Humeral blotch usually not as conspicuous as in preserved specimens.Dark lateral longitudinal line most evident posterior to vertical through base of first dorsal-fin ray and extending to end of caudal peduncle.Dorsal, anal, and caudal fins with proximate areas of rays and interradial membranes yellowish or reddish-orange.Distal portion of those fins clearer.Pectoral and pelvic fin hyaline to yellowish.
Sexual dimorphism.Bony hooks were observed over first to sixth branched anal-fin rays in various male specimens of 26.0 to 37.2 mm SL.One to six hooks occurs per ray, being two or three hooks the usual condition.Two specimens have one or two hooks also over the longest unbranched ray.The observed hooks are relatively small, similar in size, and distributed on distal portion of rays.

Ecological notes.
The riacho Três Morros is a clear headwater stream, with low to medium water current, sandy bottom, greatest depth of 1.30 m, width of 0.8 to 4.5 m and with a relatively large amount of riparian and submerged vegetation.The córrego das Piabas, a smaller stream nearby, had small amount of water (less than 50 cm deep) probably in consequence of the dry season, and several specimens where trapped in a small sandy pool.On the smallest stream only H. piatan was sampled and on riacho Três Morros only Hoplias sp.occurs syntopically.The analysis of the stomach contents of four specimens revealed presence of larvae and adult fragments of Trichoptera, adult Diptera, fragments of unidentified arthropods, large amount of filamentous algae, and organic debris.
Etymology.Named after Piatã, the county where the species is found.A noun in apposition.

Discussion
The monophyly of Hasemania, traditionally based mainly on the lack of an adipose fin, has been questioned by several authors (Böhlke, 1958;Géry, 1972Géry, , 1977;;Weitzman & Malabarba, 1999;Lima & Gerhard, 2001).However, preliminary results of a phylogenetic study of the genus ongoing by one of us (JPS) apparently suggest the group as monophyletic, based on a series of morphological characters.The phylogenetic position of Hasemania piatan within the genus is also under evaluation and the results so far indicate a putative close relationship with H. crenuchoides.These two species share some apparently derived characters, as presence of five infraorbital bones and absence of a rhinosphenoid.This last structure, present in congeners and other small characids, is not ossified in H. crenuchoides and H. piatan, with a cartilage lying in that position.Hasemania piatan and H. crenuchoides possess a single ossification in the position primitively occupied by infraorbitals three and four, possibly due to fusion of these two ossifications or loss of one of these bones.
Contrary to the common condition of members of the family Characidae that possess 19 principal caudal-fin rays, all examined specimens of Hasemania piatan have only 18 rays, a pattern unique to the species among congeners.Presence of seven branched dorsal-fin rays is also unusual within small characids lacking the supraorbital, being cited previously only for a few Xenurobryconins (Malabarba & Weitzman, 2003:82).The possession of six or fewer branched pelvic-fin rays is also rare among characids but usual among Hasemania species, except in H. hanseni.Some of the characters observed in H. piatan, such as the reduction in the number of infraorbital bones, were previously cited for other small characids from headwaters of Paraguaçu and Itapicuru rivers, both also described for elevated areas of Chapada Diamantina (Zanata & Akama, 2004;Zanata & Camelier, 2008).Hasemania piatan also does not have a sheath of scales covering the anal-fin base, a condition shared only with H. kalunga and H. maxillaris within the genus, but cited previously for various characids, including Astyanax epiagos Zanata & Camelier and Myxiops aphos Zanata & Akama.Although the phylogenetic relationships between Hasemania, Myxiops and the cited species of Astyanax are not known, the last two taxa do not share the features used to define Hasemania.Furthermore, H. piatan does not possess the features cited by Zanata & Akama (2004) in the definition of the genus Myxiops.

Diagnosis. Hasemania piatan can be distinguished from its congeners by having eighteen principal caudal-fin rays (vs. nineteen
).It differs further from the majority of its congeners by the absence of scales covering the anal-fin base (vs.presence,except in H. kalunga and H. maxillaris), presence of only five infraorbitals (vs.six infraorbitals, except in H. crenuchoides), and presence of a humeral spot (vs.absence, except in H. kalunga and H. nambiquara).The new species can be further distinguished from H. hanseni, H. maxillaris and H. nambiquara by having 10-13 branched anal-fin rays(vs.16-19), and from H. crenuchoides, H. kalunga, H.
maxillaris, H. melanura, and H. nambiquara by having 10-12 circumpeduncular scales (vs.14 or 16).Hasemania piatan differs further from H. hanseni by having six branched pelvicfin rays (vs.seven), from H. maxillaris by having six branched pelvic-fin rays (vs.five) and the majority of teeth with three or more cusps (vs.conical teeth), and from H. nambiquara by the absence of a broad black lateral band (vs.presence).The new species differs also from H. nana by having 27-32 scales in the longitudinal series (vs.20-26) and 10-13 branched analfin rays (vs.13-16), and from H. melanura by having 27-32 scales in the longitudinal series (vs.23-26) and one to three maxillary teeth (vs.none).From H. crenuchoides the new species differs further by the absence of black blotch extending to median caudal-fin rays (vs.presence) and ossification in the position primitively occupied by infraorbitals three and four relatively small, not reaching the preopercle sensory canal posteriorly (vs.ossification large, reaching the preopercle sensory canal).Hasemania piatan differs also from H. kalunga by having 27-32 scales on longitudinal series (vs.33-36) and absence of caudal blotch (vs.presence).Description.Morphometric data of holotype and paratypes in Table1.Body relatively elongated and transversely rounded, somewhat flattened posterior to terminus of dorsal fin base.Greatest body depth at dorsal-fin origin.Dorsal profile of head distinctly convex from margin of upper lip to

Table 1 .
Morphometric data of holotype and paratypes of