Ageneiosus uranophthalmus , a new species of auchenipterid catfish ( Osteichthyes : Siluriformes ) from river channels of the central Amazon basin , Brazil

Ageneiosus uranophthalmus is described from river channels of the central Amazon basin, Brazil. The new species is widely distributed in the Amazon and is distinguished from its congeners by the V-shape snout and eye laterally placed and dorsally oriented, more visible in dorsal view than in ventral view. Ageneiosus uranophthalmus shows a range of variation on color pattern when compared with its congeners. This and other differences are described and discussed herein.


Introduction
Representatives of Ageneiosus La Cépède, 1803 are exclusive and widely distributed throughout lowland waters of the Neotropical region ranging from Panama, central America to Argentina, and South America (Walsh, 1990; head width, taken just posterior to the eye; eyeball diameter, taken as the largest longitudinal measure of the eyeball; snout length, from the snout tip to the anterior margin of the eye; interorbital distance, least distance between medial eye margins; predorsal length, taken from anterior edge of the first dorsal fin spine (spinelet) to the snout tip; prepelvic length, from snout tip to pelvic-fin origin; preanal length, from snout tip to anal-fin origin; pectoral-fin spine length, from origin of spine to its distal tip, not including the fleshy or flexible bony distal portion of the spine; dorsal-fin length, from origin of first branched ray to its distal tip; dorsal-fin spine length, from second spine base at junction with first spine (spinelet) to its distal tip, not including the fleshy or flexible bony distal portion; pelvic-fin length, from base to tip of first unbranched pelvic-fin ray; anal-fin base length, from anal-fin origin to posterior-most base of anal-fin insertion; projection of the snout, distance from anterior edge of mandibular symphysis to snout tip; caudal-peduncle length, from last anal-fin ray insertion to hipurals 2 and 3 joint; caudalpeduncle depth, above tip of last anal-fin ray; mouth width, transverse distance between mouth corners; end of dorsalfin base to origin of adipose-fin, from insertion of last dorsalfin ray to adipose-fin origin; second nuchal plate width, measured transversally on its base; second nuchal plate length, from its base to posterior-most tip; and distance between nares, shortest distance between rims.
Fin-ray counts include all rays.The two posterior-most dorsal-and anal-fin rays articulating to the corresponding last pterygiophore of each fin were counted as separate rays.Caudal-fin ray counts include the branched rays and the first unbranched ray of the dorsal and ventral lobes.Gill rakers were counted on the first branchial arch (ceratobranchial and epibranchial).
Osteological preparations were cleared and counterstained for cartilage and bone using the method of Taylor & van Dyke (1985).Branchiostegal rays, procurrent caudal-fin rays and vertebral counts were taken from cleared and stained specimens (c&s).In vertebral counts the fused PU1+ U1 is considered as a single bone, and the Weberian apparatus as having five elements.Osteological terminology follows Lundberg & Luckenbill (2007).
The examined specimens and comparative material were kindly made available by In the list of comparative material examined, the museum abbreviation and catalog number are followed by the total number of specimens in that lot, range of standard length, PH -photograph, ACSI -on-line image in All Catfish Species Inventory Image Base (http://acsi.acnatsci.org/base/,Morris et al., 2006) and collecting data.
jaw by shorter distance than horizontal eye diameter.Posteriormost mouth corners extending beyond vertical through posterior nostril by distance approximately equal to horizontal eye diameter.Upper and lower lips thin; poorly developed.Jaw teeth minute, slender and conical; teeth arranged in irregular rows, laterally exposed in both upper and lower jaws.Tooth patches anteriorly wide, narrowing posteriorly.Tooth patches of upper jaw almost completely exposed when mouth closed; completely exposed on posterior corner.Number of tooth rows increase with size; specimens greater than 100 mm of SL with 15-20 anterior and 5-8 posterior rows on upper jaw and 11-16 anterior and 9-13 posterior rows on lower jaw; specimens smaller than 100 mm SL with 8-15 anterior and 3-6 posterior rows on upper jaw and 9-11 anterior and 7-11 posterior rows on lower jaw.
Description.Morphometric data for holotype and 14 paratypes presented in Table 1.A medium-sized Ageneiosus, largest specimen examined 230.0 mm SL.Body relatively elongated, depth at dorsal-fin origin (13.3-17.4% SL) proportionally higher than body width (11.5-14.7%SL).Dorsal profile of body straight to concave from snout tip to dorsal-fin origin; straight to slightly concave from dorsal insertion to adipose-fin origin, gently sloping to beginning of caudal peduncle.Dorsal and ventral profiles of caudal peduncle slightly concave.Ventral profile of head straight to anterior region of isthmus; ventral profile of body slightly convex or straight to anal-fin origin; rising in a straight line along anal fin.Head depressed anteriorly, trunk and caudal peduncle progressively more compressed towards caudal fin.Lateral line complete and midlateral; canal forming irregular zig-zag pattern, with oblique, short, posteriorly directed branches in whole extension.Total vertebrae 51, being 17 precaudal (seven ribbed), and 34 caudal; first pleural rib on sixth vertebra.
Head covered by thin skin.Snout much projected anteriorly, pointed; snout length 51.6-56.9%HL.Eye small (10.2-17.3%HL), laterally placed, dorsally oriented, more visible in dorsal view than in ventral view.Single pair of maxillary barbels, small and filamentous (excepting nuptial males, see Sexual dimorphism, below); maxillary barbels in deep groove at mouth corners.Mouth wide, subterminal, and much projected anteriorly; upper jaw extending beyond lower pectoral-fin origin.Dorsal-fin spine slender, straight; strong and pungent in juveniles (smaller than 100 mm SL), becoming progressively flexible distally in adults (greater than 100 mm SL); anterior medial margin with numerous small osseous granulations along proximal half in specimens smaller than 100 mm SL, and along almost entire spine in larger specimens (excepting nuptial males, see Sexual dimorphism, below); posterior margin with medial row of widely spaced and reduced dentitions.Dorsal fin I,5 (n = 15); last branched ray very small.Adipose fin relatively small and largely variable in shape, from triangular to quadrangular shaped; its origin anterior to end of anal-fin base.Caudal fin deeply forked, with pointed lobes.Outermost branched rays twice as long as middle rays.Upper caudal-fin lobe slightly longer than lower lobe, its outer principal rays non-filamentous, 8+9 principal rays, 17 upper procurrent, 15 lower procurrent rays (n = 15).Anal-fin base longer than predorsal length, 34.6-39.4% in SL.Anal-fin origin located at or slightly posterior to vertical through tip of the innermost pelvic-fin rays.Last unbranched and three anteriormost branched anal-fin rays more developed; rays decreasing slightly in length posteriorly.
Color in alcohol.Body ground coloration white to yellowish.Brownish to black dorsolateral band extending from head to upper caudal-fin base and with variable thickness -restricted to dorsal area (in individuals smaller than 120.0 mm SL) to extending ventrally onto lateral line (in individuals greater than 190.0 mm SL).Dorsolateral band commonly broken into longitudinal series of prominent blotches or appearing somewhat mottled.Lateral and ventral surfaces of body light, with scattered dark pigmentation of variable intensity, usually concentrated on dorsal portion of body (two individuals from rio Negro, INPA 17966 and 31252, with lateral surface of body much pigmented; brownish).Dorsal surface of head completely covered with irregular mottled pattern consisting of dark brown blotches or brownish (in individuals larger than 150 mm SL).Smaller specimens (below 130 mm SL) with two dark bands running parallel from middle of snout, along each margin of fontanel, to level of dorsal-fin insertion.These bands crossed by dark area on mesethmoid and on nuchal plate.Abdomen unpigmented.Fins with marked ontogenetic variation.Smaller specimens usually with dark bands on pectoral, pelvic completely dark, anal fin with distal dark band; dorsal and caudal fins hyaline.Above 130 mm SL, general fin coloration faint, with faded dark bands on anal fin, pelvic brownish, but dark bands still present on pectoral in most specimens.In these larger specimens, dorsal fin with anteriormost rays darker; caudal fin pigmentation vary from presence of dark basal band, followed by hyaline band and dark-pointed tips of the lobes to complete hyaline.
Barbels with scattered dark chromatophores, appearing white or dark.
Sexual dimorphism.The single mature males has strong morphological modifications already known to occur in representatives of the genus.The nuchal region in nuptial males (from frontal to nuchal plates; Fig. 3) shows a much more acute angle than in females and nonbreeding males.The ossification of the maxillary barbel begins at its base and proceeds towards its tip, resulting in a small, thickened, rigid barbel, reaching beyond anterior eye margin.The dorsal and medial surfaces of the barbel are covered with sharp, unicuspid dentations; the dorsal row with eight dentations along full ext=ension of the barbel and the medial row with four dentations along distal half.
The dorsal fin is modified.The first branched dorsal-fin ray is longer than in nonbreeding males and females.The dorsal-fin spine is straight, more rigid and elongate, its length is about two times the length of the first branched ray; the anterior margin with two rows of numerous, uniformly retrorse, unicuspid dentations, becoming progressively less prominent and pungent and more concentrated proximally; rows of dentations ending proximally on a large osseous tubercle.The dorsal-fin spine of males can be hyperextended anteriorly to approximately a 45° dorso-anterior angle, instead of the near-vertical limit of females and juveniles.
The anterior portion of male anal-fin is highly modified in comparison to that in non-breeding specimens.The unbranched and the three anteriormost branched anal-fin rays are elongate and joined together, modified as a structural support for the intromittent organ.The genital pore is at the intromittent organ tip.In adult females, the unbranched and two or three anterior branched anal-fin rays are much longer than the subsequent rays.
Ecology.Juveniles of Ageneiosus uranophthalmus were taken in small bottom trawls in swiftly flowing open channels over sand, clay and detritus substrates.Approximate depth of capture between 5-30 m.The largest specimens were collected with gillnets only in the rio Uatumã.
Distribution.Ageneiosus uranophthalmus is known from the middle reaches of the Amazon Basin, Brazil (Fig. 4), mainly rio Amazonas, rio Solimões, rio Negro, rio Purus and middle rio Uatumã.
Etymology.The specific epithet, uranophthalmus, is derived from the Greek ouranos (sky, heaven) and ophthalmos (eye) in allusion to the dorsally oriented eyes.
Remarks.The new species herein described exhibit the osteological and sexually dimorphic features proposed as synapomorphic for the family Auchenipteridae (Ferraris, 1988;Royero, 1999).Within the Auchenipteridae, Ageneiosus uranophthalmus shares with its congeners the two characters states proposed by Walsh (1990) as synapomorphic for the genus: absence of mental barbels in adults, and dorsal margin of the maxillary barbel of nuptial males with enlarged, toothlike odontodes formed by outgrowths of maxillae.
More than 30 specific names were proposed in Ageneiosus.More than 20, however, have been considered synonyms of the 11 named valid species actually recognized (Walsh, 1990;Ferraris, 2003Ferraris, , 2007)).A comparative analysis with types and original descriptions allowed concluding that the diagnostic

Fig. 4 .
Fig. 4. Drainage map of northern South America illustrating the geographic distribution of Ageneiosus uranophthalmus.Type locality represented by triangle.Some symbols represent more than one locality or lot of specimens.Base map by Marilyn Weitzman.