A new MoenkhausiaEigenmann, 1903 (Ostariophysi: Characiformes) from Chapada Diamantina, rio Paraguaçu Basin, Bahia, Northeastern Brazil

*Laboratório de Biologia e Genética de Peixes, Departamento de Morfologia, IBB-UNESP, Campus de Botucatu, 18600-000 Botucatu, SP, Brazil. rbenine@ibb.unesp.br **Laboratório de Ictiologia de Ribeirão Preto (LIRP), Departamento de Biologia, FFCLRP-Universidade de São Paulo. Av. Bandeirantes, 3900, 14040-901 Ribeirão Preto, SP, Brazil. ***Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana. Rodovia BR 116, Km 03 – Campus Universitário. 44031-460 Feira de Santana, BA, Brazil. Introduction


Introduction
The genus Moenkhausia was proposed by Eigenmann (1903) and defined as comparable to Tetragonopterus but with a gently, downward curved lateral-line. Eigenmann (1917) presented a refined definition of Moenkhausia (in an identification key to the genera of Characidae) based on the presence of two parallel rows of premaxillary teeth, five or more teeth in the inner premaxillary tooth row, a completely pored lateral line, and scaled caudal-fin lobes. Due to the lack of a comprehensive phylogenetic analysis, the characters proposed by Eigenmann remain the only diagnosis for the genus and are currently used to verify the generic allocation of new species to Moenkhausia (e.g. Benine et al., 2004;Zarske et al., 2004;Lima & Birindelli, 2006;Bertaco & Lucinda, 2006). Under this concept, Moenkhausia presently includes 63 species of a great variety of shapes and pigmentation patterns. The genus is widespread in the Neotropical Cis-Andean river basins, except for those in Patagonia, with its greatest diversity occurring in the basins of the Amazon and Guianas (Lima et al., 2003). Comments about and inferences on putatively related genera and species suggest that Moenkhausia is most likely a polyphyletic genus (see Fink, 1979;Costa, 1994;Weitzman & Palmer, 1997), although it is possible that some natural groups exist in Moenkausia (Benine, 2002). A phylogenetic appraisal of this genus is being conducted by the first author.
The Chapada Diamantina forms a watershed between the rio São Francisco basin and the rivers east of that basin that discharge directly into the Atlantic Ocean. The rio Paraguaçu has its origin in the Chapada Diamantina extending for about 500 km to its estuary in the western portion of the Baía de Todos os Santos (Santos, 2005). Its headwaters host an endemic ichthyofauna (de Pinna, 1992;Britto et al., 2005). During a broad, recent fish survey conducted in this area, one of the authors (ACAS) collected a distinctive Moenkhausia species that possesses unique features among the members of the genus. Examination of samples from rio Paraguaçu in the fish collection of the Laboratório de Ictiologia de Ribeirão Preto (LIRP) yielded additional material of the species which is described herein.

Materials and Methods
The examined material in this study is deposited in the following institutions: ( Morphometric and meristic data of specimens were taken following Fink & Weitzman (1974). In the description, holotype values are in square brackets and are followed by the mode and the number of specimens from which the count was taken. Vertebral counts, which include the four vertebrae of the Weberian apparatus as one element and the terminal centrum, were taken from four cleared and stained (C&S) specimens. Specimens were cleared and counterstained following the method of Taylor & Van Dyke (1985). duncle origin. Prepelvic region transversely flattened, flattening more pronounced proximate to pelvic-fin insertion. Postpelvic median keel extending from pelvic-fin insertion to anal-fin origin. Mouth terminal, with lower jaw as long as or somewhat longer than upper jaw. Premaxillary teeth in two rows; outer row teeth 2-5 [2] (mode= 4, n = 32), with 3-5 cusps, midcentral cusp longer than others; inner row teeth 5-6 [value of holotype], with 4-5 cusps and rarely one most lateral tooth with 3 cusps, midcentral cusp longer than others. Maxillary teeth 2-4 [2] (mode = 2, n = 30), with 3 cusps. Dentary teeth 4-5, with 4-5 cusps, midcentral cusp longer than others, [holotype with 5 teeth in left side and 4 teeth in right side, two specimens with 4 teeth in the left side and 5 teeth in right side] (mode=5, n=30), followed by series of small teeth with 1-3 cusps (Fig. 2).

Moenkhausia diamantina, new species
Tip of supraoccipital spine extending posterior beyond vertical through posterior margin of opercle.

Sexual dimorphism.
Very small hooks present on the segments of the first two branched anal-fin rays (one hook per segment). Only one male (58.5 mm SL) with small hooks on the segments of first two branched pelvic-fin rays (one hook per segment).

Color in alcohol.
Overall coloration brown or yellow tannish. Dorsal and dorsolateral portion of head, and mid-dorsal body region dark brown. Dark chromatophores scattered on infraorbitals, opercle, and branchiostegal rays. Jaws homogeneously covered with dark chromatophores. Posterior margin of scales with brown chromatophores outlining scales resulting in reticulated color pattern. Humeral region with conspicuous dark vertical blotch followed by light blotch. Caudal peduncle with an inconspicuous darker region. Dorsal fin dark with concentration of dark chromatophores on anterior two-thirds. Adipose fin densely pigmented by dark chromatophores. Pectoral, pelvic, and anal fins dark with concentration of dark pigmentation on anterior rays. Caudal fin homogeneously dark.

Distribution and habitat.
Known from the upper and middle course of rio Paraguaçu which have several relatively small tributaries entering its margins. The species was collected in seven tributaries of rio São José and Santo Antônio, two of the main tributaries of the upper course of rio Paraguaçu. These tributaries are all blackwater rivers. The type locality of Moenkhausia diamantina, the rio Toalhas, has a sandy and rocky bottom, with little riparian and submerged vegetation.
Etymology. The name diamantina is in reference to the type region, the Chapada Diamantina. A noun in apposition. Costa (1994) (2002) for the palatine and ectopterygoid bones. That could be indicative of a close relationship between M. diamantina and the above-mentioned species. Nonetheless, these characters seem to be relatively widespread among characids and need to be evaluated in a more comprehensive phylogenetic context before a rigorous hypothesis of relationships is proposed.