REVUE SUlSSE DE ZOOLOGIE 111 (4): 715-728; décembre 2004 A new genus and species of small characid (Ostariophysi, Characidae) from the upper río Bermejo basin, northwestern Argentina Juan Marcos MIRANDEl, Gastón AGUILERAl & María de las Mercedes AZPELICUETA2 1Fundación Miguel Lillo, Miguel Lillo 251, 4000 Tucumán, Argentina. E-mail: mcpiranha@hotmail.com. 2División Zoología Vertebrados,Facultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata, Argentina. E-mail: azpeli@museo.fcnym.unlp.edu.ar A new genus and species of small characid (Ostariophysi, Characidae) from the upper río Bermejo basin, northwestern Argentina. A new genus and species of small characid is described in this paper. The new genus, Nans gen. n., is diagnosed by the combination of: ii,7-8 dorsal-fin rays, 10-15 branched anal-fin rays, 5 teeth in the inner premaxillary row, rotation of the pelvic bone about 90°, rotation of the pelvic fin muscles, pelvic fin curved and forming a complete tube in mature males, incomplete foramen for exit of the olfactory nerve in the lateral ethmoid. Other characters which help in the identification of Nans are the large subcircular foramen in the dorsal vomerine lamella which articulates with the mesethmoid, the absence of an extrascapular sensory canal in the postemporal, and a laterosensory canal in the anguloarticular. The type species, Nans indefessus sp. n. was collected in the río Anta Muerta and arroyo Colorado, tributaries of the río Blanco, and in the río Pescado, upper río Bermejo basin, Salta, Argentina. - Keywords: Characiformes basin. - Characidae - Nans - new genus - río Bermejo INTRODUCTION The río Bermejo originates in northwestem Argentina and southem Bolivia, forming the politicallimit between both countries; it flows into the río Paraguay after 1,450 km. The fishes of the upper río Bermejo basin were almost unknown until few years ago. Fowler (1940) published a list about the ichthyofauna of the río Lipeo, including 14 species, four of them new for science. More recently, Femández (1999) cited 23 fish species found in the National Park Tariquía, southem Bolivia. In a recent exploration of some rivers and streams of the upper río Bermejo basin, the first and second authors collected 31 species of fishes (Mirande & Aguilera, Manuscript accepted 26.05.2004 n '1 716 J. M. MlRANDE ET AL. in prep.), incIuding specimens of an unknown species. The possession of several distinctive characters excIudes this species from other nominal genera of characids. We describe it as a new genus and a new species. MATERIALAND METHODS Measurements are straight distances taken with caliper to the nearest 0.1 mID. Measurements are expressed as percentages of SL or the indicated length. PeduncIe 1ength was measured from the insertion of the posteriormost anal-fin ray to the hypural joint. Some specimens examined in this study were cIeared and counterstained (C&S) following Taylor & Van Dyke (1985). Vertebrae counts incIude the four vertebrae of the Weberian apparatus and the caudal CP1+U1 as one e1ement. Material is deposited in the following collections: Asociación Ictiológica, La Plata (Al); Facultad de Ciencias Naturales y Museo, La Plata (MLP); Facultad de Ciencias, Sección Genética, Montevideo (MVD-SG); Fundación Miguel Lillo, Tucumán (CI-FML); Museo de Ciencias Naturales de Salta (MCNi), and Museum d'histoire naturelle de Geneve, Switzerland (MHNG). Comparative material (SL in mm). Acrobrycon tarijae: CI-FML 3270, 1 ex., 66.6 mm, Argentina, Salta, Orán, La Bambú, río Bermejo basin, río Blanco. Aphyocharax paraguayensis: Al 142,2 ex. C&S, 18.6-23.3 mm, Argentina, Formosa, flood plain of río Bermejo, in Reserva Ecológica El Bagual. Astyanax eigenmanniorum:ANSP 21627, paratypes, 2 ex., 42.5-49.4 mm, Brazil, Rio Grande do Sul. Astyanax latens: Al 112,2 ex. C&S, 41.0-45.0 mm,Argentina, Salta, Orán, arroyo El Oculto. Astyanax lineatus: CI-FML 3272, 3 ex., 35.3-72.1 mm, Argentina, Salta, Orán, La Bambú, río Bermejo basin, río Blanco. Astyanax tupi: Al 128,4 ex., 60.8-70.0 mm, Argentina, Misiones, Paraná basin, arroyo Cuñapirú Chico. Bryconamericus agna: FML 3700, holotype, 61.5 mm, Argentina, Misiones, arroyo Tabay, Paraná basin; Al 141, I ex. C&S, 60.0 mm, Argentina, Misiones, Paraná basin, arroyo Tabay.Bryconamericus iheringii: Al 116,3 ex. C&S, 39.9-44.3 mm, Brazil, Rio Grande do Sul, Silo Louren~o do Sul, arroios Pinto e Viúva Teresa. Bryconamericus thomasi: CI-FML 1969, 94 ex. (2 males, 3 females measured), 40.355.4 mm, Argentina, Salta, río Piedras. Bryconamericus exodon: MLP 18-IX-80-1, 2 ex., 39.043.5 mm, Argentina, Buenos Aires, río de la Plata in Punta Lara. Characidium sp.: Al 153, 1 ex. C&S, 29.6 mm, Argentina, Misiones, arroyo Zaimán near its mouth. Cheirodon interruptus: CIFML 3825, 2 ex. C&S, 32.9-33.4 mm, Argentina, Santiago del Estero, Embalse río Hondo; Al 160, I ex. C&S, 34.0 mm, Argentina, Buenos Aires, Mar Chiquita coastallagoon. Ctenobrycon alleni: MLP 6774, 5 ex., 50.0-64.2 mm, Argentina, Santa Fe, laguna Setúbal. Cyanocharax albumus: MVD-SG 59, 1 ex. C&S, 42.5 mm, Uruguay, río Yaguarón in Paso Centurión. Diapoma speculiferum: Al 151, 1 ex. C&S, 42.6 mm, Brazil, Rio Grande do Sul, Barra de Ribeiro, A~ude dos Garcia. Gymnocharacinus bergi: Al 143, 1 ex. C&S, 52.4 mm, Argentina, río Negro, arroyo Valcheta. Gymnocorymbus temetzi: CI-FML 3826,2 ex. C&S, 33.7-35.6 mm, Paraguay,Alto Paraguay, Fortín Patria, río Negro. Hemigrammus ulreyi:Al 161, 1ex. C&S, 34.2 mm, Argentina, Misiones, Nemesio Parma, río Paraná. Hemigrammus erythrozonus: CI-FML 3827,2 ex. C&S, 25.5-26.9 mm, aquarium specimen. Hyphessobrycon boulengeri: MVD-SG 122,1 ex. C&S, 38.1 mm, Uruguay,Rocha, río Yaguarón.Hyphessobrycon meridionalis:Al 145, 2 ex. C&S, 26.5-32.0 mm, Argentina, Buenos Aires, Berazategui, lago del Parque Pereyra Iraola. Hypobrycon maromba: Al 140, 3 ex., 45.5-47.5 mm, Brazil, Santa Catarina, Concordia, no Jacutinga. Hypobrycon poi: MLP 9573, holotype, 50.5 mm, Argentina, Misiones, arroyo Once Vueltas. 1 ex. C&S, 45.5 mm, Argentina, Misiones, arroyo Once Vueltas. Markiana nigripinnis: Al 144, 1 ex. C&S, 71.0 mm, Argentina, Formosa, flood plain of río Bermejo, in Reserva Ecológica El Bagual. Mimagoniates inequalis: MVD-SG 119, I ex., 30.0 mm, Uruguay, Departamento Rocha, environments close to Laguna Castillos. Moenkhausia cf. intermedia: CIFML 3257,60 ex. (5 measured), 20.1-31.5 mm, Argentina, Salta, Orán, La Bambú, río Bermejo basin, arroyo El Oculto. Moenkhausia sanctaefilomenae: Al 158, I ex. C&S, 31.7 mm, Argentina, Misiones, río Paraná near Posadas. Odontostilbe microcephala:CI-FML 3369, 2 ex., NEW GENUS ANO SPECIES OF CHARACIDAE 717 48.2-51.6 mm, Argentina, Salta, La Bambú, río Bennejo basin, río Blanco. Odontostilbe pequira: CI-FML 3451,1 ex., 31.5 mm, Argentina, Salta, Rivadavia, río Bennejo basin, Pozo de los Yacarés. Oligosarcus bolivianus: CI-FML 3277, 4 ex., 89.8-113.8 mm, Argentina, Salta, Orán, La Bambú, río Bennejo basin, río Blanco. Poptella paraguayensis: Al 148, 1 ex., 50 mm, Argentina, Misiones, río Piray-Miní, in Eldorado. Prionobrama paraguayensis: Al 149, 1 ex. C&S, 35.5 mm, Argentina, Chaco, flood plain of río Tragadero. Psellogrammus kennedyi: Al 150, 2 ex. C&S, 37.4-39.0 mm, Argentina, Fonnosa, flood plain of río Bennejo, in Reserva Ecológica El Bagual. Roeboides paranensis: Al 155, 1ex. C&S, 39.2 mm, Argentina, Corrientes, río Riachuelo. Serrapinus microdon: Al 152,2 ex. C&S, 25.5-29.0 mm, Argentina, Fonnosa, flood plain of río Bennejo, in Reserva Ecológica El Bagual. Serrasalmus maculatus: CI-FML 3827, 1 ex. C&S, 69.2 mm, Argentina, Salta, La Unión, Pozo de los Yacarés, río Bennejo. Tetragonopterusargenteus:Al 156,2 ex. C&S, 55.5-60.0 mm, Argentina, Corrientes, flood plain of río Riachuelo. Triportheusparanensis: Al 154, 1ex. C&S, 129 mm, Argentina, Buenos Aires, río de la Plata, in Atalaya. RESULTS Nans gen. n. Type species. Nans indefessus sp. n. Diagnosis. Nans is a new genus of small characifonns placed within the family Characidae in light of the absence of characters indicating relationships with other families of the order. Nans is identified by several probably apomorphic characters: 1- the dorsal fin with ii,7-8 rays, 2- the rotation ofthe pelvic bone about 90°; 3- rotation of the pelvic fin musc1es; 4- the pelvic fins curved, forming a tubular structure in mature males; 5- the incomplete foramen for exit of olfactory nerve in the lateral ethmoid;6- the postemporal without an extrascapular sensory canal; and 7- the absence of latero sensory canal segment in the anguloarticular. The following characters, which are present in other species of characids, also help in the identificationof Nans, the anal fin with 10-15 branched rays; the reduction of size of infraorbitals 2 and 3; the variable infraorbital number, ranging from 4 to 9; the loss of supraorbital; the short, blunt sphenotic spine; the two rows of ossified gill rakers on the anteroextemal and posteromedial margins of the first to fourth gill arches; the small anterior fenestra between the c1eithrum and coracoid in adults; the high number of supraneurals (7-8); the similar number of precaudal and caudal vertebrae; and the naked isthmus. Etymology.Nans is a latin word that means swimmer in allusion to the habit of the new genus specimens of living in torrents. Gender masculine. Nans indefessus sp. n. Figs 1-6, Table 1 Holotype. CI-FML 4000, male, 49.4 mm SL, Argentina, Salta, Orán, río Bennejo basin, río Pescado at Estancia Anta Muerta (22°54.3' S - 64°28.2' W); con. Mirande, Aguilera & Padilla, August 5, 2003. Paratypes.Al 107, 1ex. C&S, 42.8 mm SL; Al 138, 1 ex., 41.6 mm SL, Argentina, Salta, Orán, río Anta Muerta tributary of río Blanco; con. Mirande, Aguilera & Ferro, May 2002. Al 157, 3 ex., 39.7-51.7 mm SL, Argentina, Salta, Orán, arroyo Colorado, tributary of río Blanco; con. Mirande,Aguilera & Ferro, May 2002. CI-FML 4001,4 ex., 32.0-41.1 mm SL; MNHNG 2643.87,6 ex., 31.5-40.9 mm SL; MCNi 911, 2 ex., 30.1-33.2 mm SL, conected with the holotype. CI-FML 4002, 1 ex., 28.4 mm SL, Argentina, Salta, Orán, El Oculto, río Blanco; con. Mirande, Aguilera & Quoirin, October 2001. CI-FML 4003,3 ex., 41.6-44.5 mm SL, río Anta Muerta, tributary of río Blanco; con. Mirande, Aguilera & Ferro, May 2002. 718 J. M. MIRANDE ET AL. Diagnosis. As for the genus. Description. Morphometrics of holotype and 18 paratypes are presented in table 1. Body subcircular in cross section, more laterally compressed posteriorly; maximum body depth just anterior to dorsal-fin insertion. Dorsal profile of body straight or scarcely convex between snout and dorsal-fin origin; straight posterior of base of that fin. Dorsal and ventral profiles of caudal peduncle straight or ventral scarcely concave. Ventral profile from lower jaw to pelvic-fin origin convex, almost straight or slightly convex between pelvic and anal-fin insertions, slightly convex above anal-fin base in females and juveniles, markedly so in males; abruptly slanted dorsally, especially in males. TABLE1. Nans indefessus gen. n., sp. n. Morphometrics of male holotype and 18 paratypes. Minimum, maximum, and mean :t standard deviation in brackets. SL is measured in mm. SL % of standard length Predorsal distance Preanal distance PrepectoraI distance Body depth Dorsal-fin base Anal-fin base Pectoral-fin length Pelvic-fin length Pectoral-pelvic fin origins Pelvic-anal fin origins Head length Pedunc1edepth Pedunc1elength % of head length Snout length OrbitaI diameter Interorbital width Maxillary length Premaxillary+max. length PostorbitaI length Holotype 49.4 Females (n=9) 28.4-51.7 Males (n=lO) 31.5-49.4 51.4 63.6 19.2 31.7 13.2 18.2 23.3 16.3 26.0 19.2 26.8 13.8 24.6 52.0-57.7 63.4-71.2 16.0-20.5 27.5-32.1 11.1-12.9 14.1-19.8 21.4-23.4 14.4-15.6 25.6-30.6 16.0-20.5 24.7-28.7 12.3-14.6 20.5-22.8 (53.9:tl.9) (66.1:t2.6) (18.4:t1.6) (29.5:t1.6) (11.8:tO.6) (16.8:t1.6) (22.4:tO.7) (15.0:t0.5) (27.6:t1.7) (18.4:t1.6) (27.1:t1.4) (13.3:tO.7) (21.4:tO.9) 51.0-53.2 62.1-67.4 16.9-20.5 28.7-33.3 11.8-13.3 15.7-19.5 22.6-25.5 15.0-18.0 23.4-27.5 16.9-20.5 25.8-30.4 12.6-14.4 20.6-24.6 (52.0:tO.9) (64.4:t1. 7) (18.4:t1.1) (30.6:t1.4) (12.6:tO.6) (17.5:t1.2) (24.2:tO.9) (16.6:tO.8) (26.1:t1.2) (18.4:tl,l) (27 .5:tl.4) (13.5:tO.6) (22.4:t1.4) 23.2 27.8 29.3 24.4 36.5 50.7 19.3-25.1 28.5-34.4 27.0-30.4 20.6-25.4 36.9-39.6 46.9-58.4 (22.6:t2.1) (30.4:t2.2) (28.9:tl.2) (22.7:t1.5) (38.0:t0.9) (50.5:t3.9) 19.7-23.5 25.5-33.6 26.6-30.6 18.9-26.7 32.4-40.9 44.7-52.7 (21.8:t1.4) (29.7:t2.7) (28.3:t1.1) (22.9:t2.5) (38.3:t2.6) (49.0:t2.6) Dorsal-fin origin situated almost equidistant from snout and caudal-fin base. Small adipose fin located posterior to vertical through base of posterior most anal-fin rayoPelvic-fin insertion lightly anterior to vertical through dorsal-fin insertion. Anal-fin origin located at a vertical through base of posteriormost dorsal fin. Pectoral and pelvic fins short, not reaching vertical through pelvic fin insertion or anal-fin origin respectively. Dorsal fin with ii,7-8 rays (7 in 2 ex. including holotype, 8 in 16 ex.); posterior margin rounded, bearing first two or three branched rays longest. Anal fin with iiiiv,lO-15 rays (10 in 1 ex., 11 in 4 ex. including holotype, 12 in 7 ex., 5 in 5 ex., 14 in 1 ex., 15 in 1 ex.). First branched anal-fin rays longest, their length equal to or scarcely longer than base of anal fin. Distal margin of anal fin straight more so in males, and very slightly concave in females. Hooks on anal fin absent. NEW GENUS ANO SPECIES OF CHARACIDAE 719 FIG.l Nans indefessus gen. n. and sp. n., holotype, 49.4 mm SL, maleo Caudal fin emarginate, with lower lobe slightly broader and longer than upper lobe. Caudal-finrays numbers variable (10+6 branched and 1 unbranched rays in lower lobe in 1 ex., 10+7 branched and 1 unbranched rays in lower lobe in 1 ex., 9+7 branched and 1 unbranched rays in lower lobe in 1 ex., IO+S branched and 1 unbranched rays in lower lobe in 16 ex. including holotype). Pectoral fin with i,IO-13 rays (10 in 5 ex., 11 in 10 ex. including holotype, 12 in 3 ex., 13 in 1 ex.). Distal margin of fin rounded. Pelvic fin with pelvic splint and i,7S rays (7 in 17 ex. including holotype, S in 2 ex.). Males with strong hooks on al1 branched pelvic-fin rays, even in smallest specimens (Figs 2, 3). Hooks directed anteriorly,one per segment even in unbranched portion of rays, and distributed along all ray branches. Dorsal profile of snout strongly convex from snout tip to vertical through anterior margin of eye. Head profile slightly convex or straight from that point to top of supraoccipitalspine. Mouth terminal, situated just under middle of eye. Eye notably larger than snout. Infraorbitals reduced in size, with ventral margins distant from preopercular sensory canal, leaving a wide area of underlying musculature covered only by skin. Premaxilla with acute ascending process and short alveolar ramus. Premaxilla bearing two series of teeth; external row with teeth shorter than those of posterior row. Outer tooth series with 2 (1 ex.), 3 (13 ex. including holotype), or 4 (5 ex.) teeth; teeth anteroposteriorly compressed only distally. Inner premaxillary tooth series with 5 conical teeth, compressed only distally, bearing three cusps. Fifth tooth smaller, and slightly posterior to proximate tooth. Maxilla with slender dorsal process and long, relatively narrow, laminar process. Maxilla with 4 (10 ex.), 5 (S ex.), or 6 (1 ex.) tricuspid,slender,and distally compressed teeth. Dentary bearing S-lO slight1yconical teeth, compressed only distally, with one to three cusps; first four teeth 1arger,with followingteeth smaller. 720 J. M. MIRANDE El' AL. FIG.2 Nans indefessus gen. n. and sp. n., ventral view of right pelvic girdle. Scale bar: 1 rnm. Scales cycloid, with anterior margin rounded, and circuli absent in posterior fie1d.No radii anterior1ydirected. Perforated scales on 1ateral1ine36 (3 ex.), 37 (8 ex.), 38 (4 ex.), 39 (2 ex. including ho1otype),40 (2 ex.). Five (14 ex.) or 6 (5 ex.) scales between 1ateralline and dorsal-finorigin and 4.5 scales between 1ateralline and pe1vicfin origino Fourteen or 15 scales between supraoccipital tip and dorsal-fin origino Thirteen or 14 scales around caudal peduncle. Most specimens with two rows composed of 4-6 sca1eson anal-fin base, few specimens with 5-6 scales in one row; scales always covering first 6 anal-fin rays. Few scales on caudal-fin base. Isthmus naked. Four cleared and stained specimens with 13 ribs, 35-36 total vertebrae; 7-8 supraneurals; 10-11 dorsal procurrent rays and 9-10 ventral procurrent rays in caudal fin. Two rows of ossified gill rakers on 1st to 4th branchial arches. First arch with 1-2 gill rakers on hypobranchial, 5-6 on ceratobranchial, 1 on cartilage, 2-4 on epibranchial along antero1ateralmargin; and 3-4 rakers on ceratobranchial, 1 on cartilage, 3-4 on epibranchial along posteromedial margino Colorin life.Backgroundsilvery,withdorsalportíonof flanksdarker.Metallic gold lateral band visible, although faint. Notable b1ack humeral spot, vertícal1y expanded, narrow. Dorsal, anal, and caudal fins light pink to intense red. Anterior most dorsal and anal-fin rays white. Color in alcohol. Background yellowish. Upper part of flanks with chromatophores forrning light, reticu1ate pattem. UniforrnIy wide lateral band light grey, beginning close to humeral spot and ending on midd1e of caudal peduncle. Grey humeral spot vertical1y-expanded,extending from horizontal through dorsal margin of orbital, to horizontal through ventral margin of preopercle. Humeral spot very narrow in many specimens. Dorsal fin with numerous chromatophores on membranes, forrning a diffuse spot, occupying basal two thirds of fin. Anal fin with scattered chromatophores on membranes. Adipose, caudal, pectoral and pe1vicfins hyaline. Dark narrow line on dorsal portíon of body between supraoccipital and caudal peduncle. Dorsal portíon of head grey. Few chromatophores present on premaxilla, maxilla, and around infraorbitals. Chromatophores concentrated and forrning two b1ackspots on dorsal and ventral regions of eye. Some specimens with chromatophores concentrated on upper preopercu1arprocess and on preopercular articular area. Sexual dimorphism. The rotation of the pe1vicbone is present also in females, although the curvature of the pe1vicfin is more pronounced in males. In mature males NEW GENUS ANO SPECIES OF CHARACIDAE 721 FIG.3 Nans indefessus gen. n. and sp. n., detail of pelvic fin of one paratype, CI-FML 4003, 44.5 mm SL, male. both pelvic finsfono a tubular structure which is always absent in females. The females have relatively longer length between snout tip and insertion of first dorsal-fin ray, and also between origins of pectoral and pelvic fins. The males have relatively longer pectoral and pelvic fins and caudal peduncle. Etymology. The specific name indefessus is a latin adjective that means un tiring, in allusion to the high velocity of the water in which the specimens were collected. Distribution.The specimens were collected in the río Anta Muerta and arroyo Colorado, tributaries of the río Blanco, and in the río Pescado; all in the upper río Bermejo basin, in the province of Salta, Argentina (Fig. 4). The specimens were collected in areas of the streams or rivers with gravel bottom, low depth, and clear, rapidly ftowing water. Submerged vegetation was scarce. DISCUSSION Under the traditional concept of Astyanax (Eigenmann, 1921, 1927), Nans should be included in that genus because both genera share the premaxilla with five teeth in a second series, complete lateralline, the caudal fin naked, and absence of predorsal spine. Nonetheless, Nans has many characters that distinguishes it from Astyanax. The dorsal fin with two unbranched plus seven or eight branched rays is present in Nans, whereasAstyanax has the dorsal fin with two or three unbranched and nine branched rays, considered as the primitive condition of the character. Nans has 722 J. M. MIRANDE ET AL. 64° Enlarged area ~ Rlo Grande de Tarija 40 km Tropic of Capricom FIG.4 Geographical known distribution of Nans indefessus gen. n. and sp. n. in the upper río Bermejo basin, Orán, province of Salta, Argentina. 1, type locality, río Pescado at Estancia Anta Muerta. 2, río Anta Muerta, tributary of río Blanco. 3, arroyo Colorado, tributary of río Blanco. 4, El Oculto, río Blanco. short anal fin with 10-15 branched rays. In contrast, Astyanax has longer anal fin with more than 18 branched rays, exc1udedA. brachypterygium, A. cremnobates, and A. jenynsii (Bertaco & Malabarba, 2001). Nans has the infraorbitals 2 and 3 reduced in size, with their ventral margins distant from preopercular sensory canal; the ventral margins of the infraorbitals 2 and 3 are situated very near to preopercular sensory canal in Astyanax, this is the cornmon condition among characids. AIso, Nans has the anterior portion of body subcircular in cross section and Astyanax has that portion of body laterally compressed. In Nans, the gill rakers on first ceratobranchial are short, conical, and located in two rows whereas Astyanax has long, setiform gill rakers located in one row. The scales of Nans have rounded anterior margin (vs. straight in Astyanax). The isthmus is naked in Nans and it is covered with scales in Astyanax. The premaxillary and dentary teeth of Nans are conical although their distal tips are compressed and bear three cusps; in Astyanax, premaxillary and dentary teeth have broad crowns with NEW GENUS ANO SPECIES OF CHARACIDAE 723 " FIG.5 Nans indefessus gen. n. and sp. n., right anterolateral view of snout bones. Olfactory foramen partially bounded by cartilage; a large foramen placed in dorsomedial vomerine lamella for articulation with mesethmoid. Scale bar: 1 mm. denticulatedfree marginoThe dorsal margin of dentary between coronoid process and symphysis abruptly tapers ventrally in Nans, ressembling that of Bryconamericus, whereas the same margin is almost straight in the dentary of Astyanax. Many osteological characters differentiate Nans from Astyanax: blunt sphenotic spine (vs. long sphenotic spine in Astyanax); very short supraoccipital spine (vs. relatively long); seven or eight supraneurals (vs. four to six); large orbitosphenoid with its anteroventral marginnear parasphenoid (vs. short orbitosphenoid); slender postcleithrum 3 (vs. postcleithrum 3 with laminar portíon); the short nasals do not surpass the lateral wings of mesethmoid (vs. long nasals, surpassing the lateral wings of mesethmoid); the olfactory foramen is partially bounded by cartilage in Nans whereas it is completely bounded by bone in Astyanax. The latter and other characters present in Nans are discussed below. .. .. - 724 J. M. MlRANDE ET AL. FIa.6 Nans indefessus gen. n. and sp. n., left lateral view of extrascapula, postemporal and supracleithrum. Sensory canals developed on extrascapula and supracleithrum; a sensory canal is absent on postemporal. Scale bar= 1 mm. The new genus lacks the synapomorphies of phylogenetically defined subfamilies or genera, such as the Glandulocaudinae (Weitzman & Fink, 1985;Weitzman et al., 1994; Weitzman & Ortega, 1995; Weitzman & Menezes, 1998), Cheirodontinae (Malabarba, 1998), Stethaprioninae (Reis, 1989), Serrasalminae (Machado Allison, 1983), and the genera Moojenichthys (Castro & Vari, 1990), Hypobrycon (Malabarba & Malabarba, 1994), Jupiaba (Zanata, 1997), Attonitus (Vari & Ortega, 2000), Caiapobrycon (Malabarba & Vari, 2000), Creagrutus and Piabina (Vari & Harold, 2001), and Deuterodon (Lucena & Lucena, 2002). The following characters are pertinent to the question of the phylogenetic placement of the new genus: 1- The presence of ii,7-8 dorsal fin rays in Nans, separates it from most genera of characids. Recently, Malabarba & Weitzman (2003) published the description of Cyanocharax, including the phylogenetic diagnosis of a putative clade A which is diagnosed by the presence of ii,8 dorsal-fin rays and 4 teeth in the inner premaxillary row. The first synapomorphy is present in Nans which, however, always have 5 premaxillary teeth in the inner row. Furthermore, the terminal mouth of Nans distinguishes it from genera included in clade A, all of which have ventrally-locatedmouths, or modified teeth. The genus Cyanocharax, with terminal mouth and generalized teeth, has 6 branched pelvic-fin rays in contrast to the pelvic fin of Nans with 7-8 branched rays. Modifications related to sexual dimorphism are often found in characids. Males of different genera of Glandulocaudinae (Weitzman & Fink, 1983; Weitzman & Fink, 1985; Menezes & Weitzman, 1990), Cheirodontinae (Malabarba, 1998), and many tetragonopterins have hooks variably present on the anal and pelvic fins; some tetragonopterins also have hooks on pectoral, caudal, and/or dorsal fins. Modifications of the pelvic girdle such as those present in Jupiaba (Zanata, 1997), are uncornmon in characids. Nans has three possibly autapomorphic characters related to the pelvic girdle, and pelvic muscles. 2- In most characids, the pelvic bone is located in a horizontal planeoIn males and females of Nans, the pelvic bone is positioned in a vertical plane, with the primitively external, posterolateral margin of the bone shifted ventrally (Fig. 2). 3- The pelvic fish muscles are usualIy located on the dorsal and ventral surfaces of the pelvic bone {Winterbottom, 1974; Zanata, 1997). As a consequence of the NEW GENUS AND SPECIES OF CHARACIDAE 725 rotation of the pelvic bone, the muscles in Nans occupy the lateral faces of the bone, with the abductorpelvicus located lateromedially and the adductorpelvicus occupying the lateral, extemal surface. The adductor superficialis is a large muscle with many fibers covering the anterior portion of the abductors, with muscles inserting on medial surface of the pelvic bone. The arrector ventralis is very well developed, being larger than that of other examined characids (e. g. Astyanax, Bryconamericus, Markiana). 4- In the Characidae the pelvic fins usually lie in a horizontal planeo As a consequence of the rotation of the pelvic bone in Nans, the extemal unbranched rays also shift ventrally, resulting in pelvic fins with a degree of curvature, with the inner branched ray dorsomedially positionated. The curvature of the fins is most pronounced in males and most modified in mature males in which the margin of the fins overlap to form a tubular structure (Figs 2, 3), with the primitively lateral unbranched fin ray positioned ventromedially. Different modifications occur in the pelvic fins of some species of glandulocaudins, such as Scopaeocharax atopodus and Xenurobrycon macropus (Weitzman & Fink, 1985). In males of Bryconamericus thomasi, B. eigenmanni, and B. rubropictus, the curvature of the anal rays is similar to that of Nans, but in Bryconamericus species the rays are curved while the bases of the rays maintain their usual position. 5- The lateral ethmoid of characids has an opening for the olfactory foramen, as describedby Weitzman(1962) in Brycon meeki. In Nans, more than half ofthe opening for the olfactoryforamen is bounded by the lateral ethmoid (Fig. 5). The medial margin of the aperture is sorrounded by a cartilage which also contacts the large orbitosphenoid. That foramen is completely bordered by the lateral ethmoid in other examinedspecies. The rhinosphenoid is absent. Two characters that differentiate Nans from other characids are associated with the laterosensorycanal system. 6- The supratemporal canal of the laterosensory system of characids usually exits the extrascapula, passes into the posttemporal, and enters into the supratemporal.This is the most common pattem in characids such as Astyanax latens, Bryconamericus agna, Cheirodon interruptus, Gymnocorymbus temetzi, Salminus maxillosus, Gymnocharacinus bergi, Tetragonopterus argenteus, Hyphessobrycon meridionalis, and Brycon orbignyanus, and also in species of other characiform families such as Hoplias cf. malabaricus, Oligosarcus bolivianus, Thoracocharax stellatus, Steindachnerina brevipinna, and Characidium sp. (Azpelicueta, 1979). The supratemporalsensory canal is absent on the posttemporal of Nans (Fig. 6), an absence that also occurs in other species as homoplasy (e.g. Hemigrammus erythrozonus in Weitzman & Fink, 1983; peroobs.). The posttemporal of Hemigrammus ulreyi and Hyphessobryconboulengeri have a sensory canal segment. 7- The lower jaw of characids bears a sensory canal- the mandibular canal- that passes through the dentary and anguloarticular (Weitzman, 1962). The mandibular sensory canal does not develop within the anguloarticular of Nans, instead the sensory system segment runs through the skin from the dentary to the anterior limit of the preopercle. A reduction in the degree of development of sensory canals often occurs in miniature characids but Nans reaches total lengths larger than those of the miniature characids discussed by Weitzman& Vari (1988). Weitzman & Malabarba (1998) pointed out that characid species with modificationsrelated to sexual dimorphism are an excellent source of phylogenetic infor- 726 J. M. MIRANDE ET AL. mation. This may be the case of Nans, although insemination has not been studied in the genus. The relationsbips of Nans with other genera are unknown as are the relationships of many species and genera of Characidae. ACKNOWLEDGEMENTS We thank Axel Bachman (Universidad de Buenos Aires, Argentina) for bis help with nomenclatural troubles; Luiz Malabarba (Museu de Ciencias e Tecnologia, PUCRS, Porto Alegre, Brasil) and Graciela García for exchange or loan of material; one anonymous reviewer who greatly improved the English style and added valuable suggestions; CONICET, Fundación Miguel Lillo and Fundación Proyungas for financial support; Ignacio Ferro, Matías Quoirín, Sebastián Barrionuevo, Guillermo Suárez, and Rogelio Yáñez for help in the collecting expeditions, and the Secretaría de Medio Ambiente y Recursos Renovables de la Provincia de Salta for collecting perrnits. REFERENCES AzpELICUETA,M. de las M. 1979. Anatomía comparada craneana y cintura pectoral de peces Characiformes. Unpublished Doctoral Thesis, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata. 100 pp. BERTACO,V. & MALBARBA,L. R. 2001. 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