A new species of the catfish genus Centromochlus ( Siluriformes : Auchenipteridae : Centromochlinae ) from the upper rio Paraná basin , Brazil

Centromochlus comprises twelve species, distributed in the main inland watersheds of South America, including the Orinoco, Essequibo, coastal rivers of Suriname, Amazon, upper Paraná and São Francisco basins. The new species is described from the upper rio Paraná based on material collected in 1965 during the construction of the UHE Ilha Solteira, São Paulo, Brazil. The new species is easily distinguished from all congeners due to absence of adipose fin, a condition otherwise restricted to Gelanoglanis nanonocticolus, among centromochlin catfishes. The new species comprises small catfishes (adults ranging from 35 to 39 mm SL), in which modified anal fin of males is devoid of denticulations or spines, and most posterior rays reduced in length. In addition, Tatia simplex Mees is transferred to Centromochlus and its generic reassignment discussed.

Species of Centromochlus are distributed widely in South American, occurring in the Orinoco basin in Venezuela and Colombia, in the Amazon basin from Ecuador to Brazil, and in the coastal rivers of northern South America between the mouths of the Orinoco and Amazon rivers from the Guianas to Brazil (Soares-Porto, 1998;Ferraris, 2003Ferraris, , 2007;;Akama & Sarmento-Soares, 2007).Centromochlus sensu Soares-Porto (1998) was defined as monophyletic group based on the following synapomorphies: elongate maxilla, about 35 to 45% longer than palatine; anterior nuchal plate absent; elongate ventrolateral process of infraorbital 1 (lacrimal), forming the anterior border of the orbital rim, with the infraorbital canal extending through this process to its tip.However, Gelanoglanis can be distinguished from Centromochlus by having only a single pair of mental barbels; premaxillary tooth patches laterally oriented and widely separated anteriorly at midline; posterior naris large and immediately anterior to eye; oblique, sinuous mouth with free fleshy flange around angle of gape, and dorsal, anal, and paired fins with short base and few rays (Soares-Porto et al., 1999).
Large hydroelectric dams were built in São Paulo, the most populous state of Brazil, working since in the 1960s.Those large dams had a significant impact on the rivers and fish communities in the upper rio Paraná basin.The Usina Hidrelétrica de Ilha Solteira was one of the first dams built between 1965 and 1978 in a stretch of rio Paraná between Ilha Solteira (São Paulo) and Selvíria (Mato Grosso do Sul).It is the third largest dam in Brazil, and together with its neighbor, UHE Engenheiro Souza Dias (also known as UHE Jupiá), the both dams compose the sixth largest hydroelectric complex in the world (Shibatta & Dias, 2006).During the construction of the UHE Ilha Solteira, expeditions to the area resulted in the capture of several species now considered rare (i.e, collected only during that opportunity or very few times in other places), including Apteronotus acidops Triques, 2011, Sternarchorhynchus britskii Campos-da-Paz, 2000, and Tembeassu marauna Triques, 1998.The first two species are listed as threatened on the Brazilian Red List (Brasil. MMA, 2014).During the same expeditions, the new species of Centromochlus was collected.The new species was incorrectly identified as Glanidium cesarpintoi, a poorly known species of Centromochlinae described by Ihering (1928) to the rio Mogi Guaçu, upper rio Paraná basin.The misidentification left the new species undescribed for more than 50 years.The aim of the present contribution is to describe the species as new, diagnosing it from all other Centromochlinae.In addition, comments on Centromochlus simplex are provided and its generic placement discussed.

Material and Methods
Osteological features were examined in cleared and stained (CS) specimens prepared according to the procedures of Taylor & Van Dyke (1985).Prior to clearing and staining, specimens were dissected when possible to determine gut contents, sexual maturity of gonads, and to check myological characteristics.Osteological data for species poorly represented in collections were obtained from radiographs.Specimens examined via radiographs are noted as "R" in the Material examined section.Nomenclature for osteological elements is based on Weitzman (1962) , Fink & Fink (1981), Arratia (2003), including suggestions by Britto (2002, 13) and Birindelli (2014); most terms follow the Zebrafish Information Network (ZFIN).Muscle names follow Sarmento- Soares & Porto (2006).Drawings were rendered from camera lucida or digital photographs, preferably of CS specimens.
Straight-line measurements were made with a digital caliper, and recorded in tenths of a millimeter.Measurements and counts follow Sarmento-Soares & Martins-Pinheiro (2008).Counts of fin rays and bony elements were obtained from alcohol-preserved and CS specimens.Vertebral counts include the five elements incorporated into the Weberian complex and one terminal element associated with the hypural complex (following Vari & Ferraris, 2013).Counts of branchiostegal rays were performed only on CS specimens.
Institutional abbreviations are as follow: American Museum of Natural History, New York (AMNH); Natural History Museum (formely British Museum Natural History

Centromochlus britskii, new species
u r n:lsid:zooban k.org:act:06BA0384 -4F94 -4FF2-BDB0 -4DFC9C584B44 Fig. 1 Glanidium cesarpintoi (non Ihering, 1928) and C. macracanthus by having posterior border of dorsalfin spine smooth (vs.with denticules); from C. punctatus by the morphology of male modified anal fin, specifically, the last branched anal-fin ray progressively shorter than anterior most (vs.last ray abruptly reduced, size half that of preceding one and visible only through dissection).
Description.Morphometric data in Table 1.Small size, examined adult specimens 33.6-39.2mm SL.Body short, head slightly depressed.In dorsal view, profile of head longer than broad, slightly convex from snout tip to pectoral-fin insertion.In lateral view, dorsal profile of body from dorsalfin base to caudal fin slightly to distinctly convex.Ventral profile of head and abdomen almost straight.Ventral profile of body gently concave between anal-fin base and caudalfin origin.Trunk from dorsal-fin base to caudal peduncle gradually compressed.Head integument thick, bones of cranial roof not discernible; adipose eyelid weakly developed; eye dorsolateral on anterior portion of head; mouth terminal, upper lip extended posterolaterally, fleshy rictal fold well developed; snout margin rounded in dorsal view; anterior nostril tubular, located on anterior border of snout; posterior nostril somewhat larger, rounded, limited anteriorly by small skin flap; transverse distance between anterior nostrils almost equal to distance between posterior ones.Maxillary barbel elongate, extending well beyond membranous border of opercle, reaching approximately vertical through dorsalfin origin; adpressed maxillary barbel fits in groove on the lateral portion of head, immediately above rictal fold and below eye; mental barbels short, tips not reaching pectoralfin base; bases of barbels arranged in arc along ventral surface of jaw; inner mental barbel about two-thirds outer mental.Posterior process of cleithrum moderately large, almost reaching vertical through base of dorsal-fin spine.
Osteological description.Rostral border of cranium with mesethmoid longer than broad; premaxilla with synchondral articulation; cranial fontanel narrowly elliptical, enclosed by mesethmoid and frontals (Fig. 2).Nasal ossified as short tubular bone situated between mesethmoid cornua and lateral ethmoid, not sutured to mesethmoid.Autopalatine rod-like, oriented almost parallel to longitudinal axis of body; maxilla very small, less than half the size of autopalatine; vomer short, arrow-shaped with lateral processes.Jaws of equal size; premaxilla and dentary slender with three or four rows of robust conical teeth.Anterior nuchal plate absent; middle nuchal plate slightly concave along lateral margins; posterior nuchal plate thin, projected laterally, with prominent tip.Epioccipital process very small.
Hyomandibula broad, projected anteriorly, connected to both quadrate and metapterygoid through cartilage and deeply dentate suture.Metapterygoid as a wide lamina, joined to quadrate via suture (Fig. 3).Quadrate trapezoidal, with broad base, sutured to preopercle, hyomandibula and metapterygoid; long preopercle ventral margins sutured to both quadrate and hyomandibula; suprapreopercle present as short canal bone; opercle laminate, ornamented and broadly subtriangular.
Hyoid arch with parurohyal well developed with a robust ventral process; short dorsal hypohyal associated with comparatively large ventral hypohyal; anterior ceratohyal well developed, posterior ceratohyal smaller than others one; branchiostegal ray articulated to hyoid arch; six branchiostegal rays, four slender rays associated with anterior ceratohyal, two flattened rays with posterior ceratohyal (Fig. 4).
Infraorbital 1 with ventro-lateral process restricted to anterior border of eye.Infraorbital series completed by four thin and canal-like bones.Lateral line on body straight, inconspicuous, with ossified canal bones only anteriorly, unbranched at caudal fin.Dorsal fin I,5, dorsal-fin spine with 9 minute serrations becoming progressively smaller towards fin base; spine smooth anteriorly and posteriorly.Pectoral fin I,5, pectoral-fin spine with 16-17 retrorse serrations along entire anterior margin; 13 retrorse serrations along posterior margin; anterior serrations smaller than posterior ones.Pelvic-fin i,5, lateral margin rounded.Adipose fin absent in all specimens.Anal fin iii,7; anal-fin pterygiophores with eight rod-like proximal radials and six cartilaginous distal radials.Caudal fin deeply forked, lobes with rounded tips, 8+9 principal rays, all branched plus first branched in each lobe; 10-14 upper and 8-13 lower procurrent rays.Ribs 9 (one specimen with 10) attached to consecutive vertebrae 6-14, becoming progressively smaller posteriorly.Total vertebrae 32 (N= 2) or 33 (3), observed in cleared and stained (CS) and radiographed specimens (R).Sexual dimorphism.Based on examination of gonads, Centromochlus britskii attains sexual maturity at about 33.0 mm SL.Abdominal cavity previously opened in all specimens, revealing most to be adults, the smallest one a maturing female.Genital papilla prominent with a small fleshy tissue around opening in females.The genital papilla of mature males is visible as an emergent deferent duct (Fig. 6, dd).The anal fin of mature males is strongly modified with all proximal radials basally fused to each other, forming a singular structure.Third unbranched ray elongated and thickened, ending in a rounded tip, together with the slim first branched ray (Fig. 6, uiii, b1).First unbranched anal-fin ray thickened and short.Second unbranched ray elongated, with an intermediate size between the neighboring first and third rays.Third unbranched ray longest, twice the width of first branched ray, bearing 13-15 segments (Fig. 6, uiii, b1).Posterior branched rays progressively shorter; last ray the smallest one (Fig. 6, b7).No tegumentary keel preceding the first unbranched anal-fin ray; denticulations absent from anterior rays.No modifications observed in the maxillary barbel and in the dorsal-fin spine of males, unlike some species of Auchenipteridae (e.g., Auchenipterus), wherein modified males have stiff and/or spiny ossified maxillary barbels, and an elongated dorsal-fin spine (Ferraris & Vari, 1999   Etymology.The specific name honors Dr. Heraldo Antonio Britski, who collected the type material, for his significant contributions and pioneer studies on the systematics of the catfish family Auchenipteridae (i.e, Britski, 1972).

Discussion
Three species of Centromochlinae occur in the upper rio Paraná basin: Tatia neivai (Ihering, 1930), Glanidium cesarpintoi, and Centromochlus britskii, described herein.Tatia neivai was described based on the unique holotype that is currently lost (Britski, 1969) The new species is particularly similar to Centromochlus simplex (see below for comments on the latter), which has a diminutive adipose fin, 6-7 branched anal-fin rays and retrorse serrations along both margins of pectoral-fin spine.The new species is distinguished from C. simplex by having an adipose fin (vs.adipose fin absent in C. britskii); 17 upper plus 15 lower caudal fin procurrent rays (vs. 9 upper plus 8 lower) and longer posterior cleithral process, 20% of SL (vs.16% of SL).The new species is also very similar to Centromochlus bockmanni, a species apparently endemic to the rio São Francisco basin.Centromochlus bockmanni is distinguished by having adipose fin (vs.absent in C. britskii), caudal fin procurrent rays 14 upper plus 13 lower (vs.9 upper plus 8 lower); pectoral-fin spine with antrorse serrations along anterior margin and retrorse serrations along posterior margin (vs.retrorse serrations along both anterior and posterior margins).
The new species is herein described in the genus Centromochlus by possessing an elongated maxilla that extends into the maxillary barbel; infraorbital 1 with an elongate ventrolateral process, forming anterior border of orbit; and a longitudinal crest on the parasphenoid and orbitosphenoid for attachment of the adductor arcus palatini (Soares-Porto, 1998;Sarmento-Soares & Porto, 2006).In addition, Centromochlus britskii lacks the features used to diagnose the other genera of Centromochlinae, namely Tatia, Glanidium and Gelanoglanis.Tatia was defined by Sarmento-Soares & Martins-Pinheiro (2008) as having hyomandibula elongated anterodorsally, not contacting the narrow metapterygoid, anal-fin base of adult males reduced and caudal peduncle compressed and deep, somewhat keeled posterior to adipose fin.Glanidium is diagnosed by having sphenotic and pterotic excavated, resulting in strongly concave lateral margin of neurocranium (Ferraris, 1988;Soares-Porto, 1998); presence of anterior nuchal plate, and anal-fin radials not completely fused in mature males.Gelanoglanis is a miniature and derived taxon of Centromochlinae with several autapomorphies (see Introduction).Although the new species is demonstrably valid, problems persist concerning the taxonomy of some species of Centromochlus.
Comments on Centromochlus simplex.Until recently, Tatia simplex Mees, 1974 was only known from the holotype collected in the rio das Mortes, rio Araguaia basin.Tatia simplex is a valid taxon within the centromochlin subfamily, a clade characterized by the following three synapomorphies, exclusive to adult males: modified anal-fin rays and proximal radials with a posterior orientation; urogenital papillae emerging from a skin flap at anal-fin origin; and proximal radials basally fused to each other, forming a single ossification (Soares-Porto, 1998).Sarmento-Soares & Martins-Pinheiro (2008) recently revised Tatia, diagnosing it based on the following exclusive characteristics: suspensorium with metapterygoid united to quadrate but not to hyomandibula and caudal peduncle with a middorsal keel posterior to adipose fin.Based on examinations of the holotype and additional specimens from the Tocantins and Xingu river basins, Sarmento-Soares & Martins-Pinheiro (2008) treated T. simplex as "Centromochlus" simplex incertae sedis in Centromochlinae because it lacks all characteristics diagnostic of Tatia (e.g., suspensorium is joined to both quadrate and hyomandibula in C. simplex).Centromochlus simplex also lacks the features used to diagnose Glanidium (Soares-Porto, 1998;Sarmento-Soares & Martins-Pinheiro, 2013), such as voluminous section A2 of the adductor mandibulae muscle associated with a deep concavity between sphenotic and pterotic, and anterior nuchal plate present.Centromochlus simplex does not share the unique features present in Gelanoglanis described in Soares-Porto et al. (1999) and Rengifo et al. (2008), already mentioned in the introduction.
At present, Centromochlus is a morphologically heterogeneous assemblage of species supported by the following synapomorphies: presence of an elongate maxilla that extends into the maxillary barbel; an elongate ventrolateral process of infraorbital 1, forming anterior border of orbit; and a longitudinal crest on the parasphenoid and orbitosphenoid for attachment of the muscle adductor arcus palatini (Soares-Porto, 1998;Sarmento-Soares & Porto, 2006).Although some variation occurs within Centromochlus and further investigation of its monophyly are necessary, C. simplex shares all those features hypothesized for Centromochlus as synapomorphies.In addition, the lack of anterior nuchal plate is a feature common to some species of Centromochlus and Gelanoglanis.Based on our observations, Tatia simplex is herein considered as a member of genus Centromochlus.

Fig. 7 .
Fig. 7. Map of southeast South America indicating the rio Paraná in UHE Ilha Solteira, type-locality of Centromochlus britskii.Ecological notes.The species is known only from a single sample in 1965, prior to the completion of UHE Ilha Solteira; specimens were collected in places with rocks and rapids near cofferdams in the main channel of the upper rio Paraná.The rio Paraná in that area is now modified as a large reservoir.Analysis of the stomach contents revealed the presence of insect larvae, including Chironomidae, and other invertebrate fragments.
, and recently redescribed (Sarmento-Soares & Martins-Pinheiro, 2008).Specimens of Centromochlus britskii were previously misidentified as Glanidium cesarpintoi (Sarmento-Soares & Buckup, 2005).Specimens recently collected confirm the distinctiveness of G. cesarpintoi and C. britskii.Glanidium cesarpintoi differs by having an adipose fin (vs.absent in C. britskii), anterior nuchal plate present (vs.absent), anal-fin radials of mature males only partially fused (vs.completely fused), anal fin with 8 branched rays (vs.7) and bearing 21-23 segments in mature males (vs.13-15).Glanidium cesarpintoi is currently known from specimens collected from its type locality, rio Mogi Guaçu, a tributary of rio Grande, rio Tibagi, a tributary of rio Paranapanema, and rio Corumbá, a tributary of rio Paranaíba (see Material Examined).The new species occurred in sympatry with Tatia neivai, in the rio Paraná prior to the Ilha Solteira reservoir.Tatia neivai has the diagnostic features of Tatia, such as the suspensorium with metapterygoid bone united to the quadrate only (vs.joined to both quadrate and hyomandibula in C. britskii; see fig. 2 in Sarmento-Soares & Martins-Pinheiro, 2008 and Fig. 3 in present paper); caudal peduncle with a middorsal keel posterior to adipose fin (vs.caudal peduncle rounded dorsally, lacking keel in C. britskii).Tatia neivai also has an anterior nuchal plate (vs.absent in C. britskii); penultimate centrum without ribs (vs.pleural ribs attached to consecutive vertebra in C. britskii); and head, body and fins dark with small pale blotches (vs.head, body and fins light brown with scattered dark chromatophores).