Leptodoras oyakawai, Birindelli & Sousa & Sabaj Pérez, 2008

Birindelli, José L. O., Sousa, Leandro M. & Sabaj Pérez, Mark H., 2008, New species of thorny catfish, genus Leptodoras Boulenger (Siluriformes: Doradidae), from Tapajós and Xingu basins, Brazil, Neotropical Ichthyology 6 (3), pp. 465-480 : 466-475

Leptodoras oyakawai , new species

Figs. 1 and 2

Holotype. MZUSP 97909 (120.5 mm SL), Brazil, Pará, Novo Progresso, rio Jamanxim (Tapajós basin), at Prainha , near Novo Progresso , 07°03’51”S 55°26’28”W, 24 Oct 2007, J. L. O. Birindelli, L. M. Sousa, M. H. Sabaj Pérez, A. Netto Ferreira, N. Lujan.

Paratypes. ANSP 187336 (1, 123.5 mm SL, 1 sk, 120 mm SL); MZUSP 97395 (2, 82.2-121.9 mm SL); collected with holotype .

Non-types. All from Brazil, Mato Grosso. Tapajós basin: ANSP 187415 (2, 63.0- 72.2 mm SL), AUM 47567 (2, 66.6-72.0 mm SL), MZUSP 95722 (5, 51.8-89.8 mm SL, 1 cs, 73.0 mm SL), Paranaíta , rio Teles Pires , near ferry boat of road MT-416, 09°27’07”S 56°30’46”W, 27 Sep 2007, L. M. Sousa, A. Netto Ferreira. INPA 28856 (2, 59.9-70.1 mm SL), MCP 42796 (1, 58.1 mm SL), MZUSP 96597 (7, 52.4-71.6 mm SL), Peixoto de Azevedo , rio Peixoto de Azevedo , tributary of rio Teles Pires , 10°13’14”S 54°58’02”W, 16 Oct 2007, J. L. O. Birindelli, L. M. Sousa, M. H. Sabaj Pérez, A. Netto Ferreira, N. Lujan. Xingu basin: ANSP 187417 (3, 86.4-96.6 mm SL), MZUSP 91979 (15, 75.6-108.7 mm SL), Campinápolis, rio Culuene , in former area of PCH Paranatinga II, 13°49’S 53°15’W, 24 Oct 2007, J. L. O. Birindelli, L. M. Sousa, A. Akama. MNRJ 31915 (3, 79.9-85.1 mm SL), MZUSP 94141 (22, 63.0- 96.3 mm SL, 1 cs, 96.0 mm SL), Gaúcha do Norte , rio Culuene , Fazenda do Sr. Zezé , ca. 2 km upstream of bridge, 13°30’53”S 53°05’40”W, 21- 26 May 2007, J. L. O. Birindelli, F. C. T. Lima, C. A. Figueiredo, F. A. Machado. MZUSP 86992 (1, 62.8 mm SL), Gaúcha do Norte , rio Culuene , 13°30’52”S 53°05’34”W, 19 Oct 2004, J. L. O. Birindelli, O. T. Oyakawa, J. C. Nolasco. MZUSP 87028 (13, 55.9- 94.8 mm SL), Gaúcha do Norte , rio Curisevo , Porto Vitório, near ribeirão Kevuaieli, 13°02’05”S 53°23’19”W, 19 Oct 2004, C. R. Moreira, M. I. Landim, A. K. Oliveira, A. Datovo. MZUSP 98216 (3, 69.9-103.5 mm SL), Campinápolis, rio Culuene , below PCH Paranatinga 2, 13°50’00”S 53°15’00”W, 02 Oct 2007, F. C. T. Lima, F. Machado, C. R. Moreira, A. Ribeiro .

Diagnosis. Leptodoras oyakawai is a member of the genus Leptodoras by having a modified oral hood (see Fig. 3 ) and the first gill arch with enlarged accessory lamellae extending well onto the medial (postaxial) face of the gill filaments (see Fig. 4 ). Leptodoras oyakawai is distinguished by three characteristics unique within Leptodoras : gas bladder moderately sized (not reduced) and with simple walls (diverticula absent; see Fig. 5 ), and paired bony capsules on anteriormost vertebrae reduced to paired cup-like laminar ossifications separated by a triangular septum (see Fig. 6 ).

Comparisons. All other species of Leptodoras have a reduced gas bladder with two large, horn-like diverticula, one extending from each posterior chamber, and a pair of smaller diverticula on each lateral wall of anterior chamber. All other species of Leptodoras also have superficial ossifications covering the anteriormost vertebrae expanded ventrally into a conjoined pair of bony capsules that are intimately associated with the anterior wall of gas bladder (see Fig. 6 ).

Leptodoras oyakawai is further distinguished from all species of Leptodoras except L. copei and L. praelongus by having basal third to half of dorsal-fin spine blackened (dark pigment also usually present along base of dorsal fin forming a triangular blotch tapered posteriorly) and lower labial extension of modified oral hood extending more posteriorly than upper labial extension (see Fig. 3 ). Leptodoras oyakawai has relatively few midlateral scutes (33-37 per side) similar to L. copei (35-37) and L. praelongus (35-38) vs. 37-46 scutes in all other species of Leptodoras .

In L. oyakawai , as in most species of Leptodoras , the anterior nuchal plate is well-developed and laterally expanded, and the parieto-supraoccipital does not contact the middle nuchal plate ( Figs. 7 a-b) vs. anterior nuchal plate reduced, permitting contact between parieto-supraoccipital and middle nuchal plate in most specimens of L. praelongus .

Description. Examined material 51.8 to 123.5 mm SL (n = 86). Measurements of holotype, paratypes and non-type specimens in Table 1. Dorsal, lateral and ventral views of holotype in Fig. 1 . Body elongate, slightly compressed, deepest at dor- sal-fin origin, gently tapering to short, slender caudal peduncle. Ventral surface flattened from mouth to anal-fin origin. Head large, deep, weakly compressed with conical snout; dorsal profile straight to weakly convex from snout tip to between anterior and posterior nares, then curving gently (convex) to interorbital region and finishing straight, weakly oblique to dorsal-fin origin. Eye large, dorsolateral, covered by thick layer of adipose tissue; dorsal margin of orbit strongly concave and medially turned; interorbital moderately narrow, 7.0-13.9% of predorsal length.

Mouth subterminal; jaws edentulous in adults and juveniles as small as 51.8 mm SL; gape rounded anteriorly and straight with slight elevation at symphysis posteriorly.

Three pairs of barbels: maxillary, inner and outer mental ( Fig. 3 ). Maxillary barbel relatively short, tip finishing shy of medialmost terminus of gill opening in adults, extending to or slightly beyond in juveniles; fimbriate with about nine secondary barbels along lateral margin; proximal ones overlapping and rugose with papillae along dorsal surface; distal ones more spaced and simple. Upper labial extension lanceolate (tapered distally), moderately elongate, relatively thick, straight to weakly curved medially, with ventral surface largely smooth or sometimes with small papillae distally. Lower labial extension narrower, attenuate, relatively straight (tip may be curled dorsally due to preservation), with ventral surface largely smooth or sometimes with small papillae/fimbriae distally. Lower labial extension finishes slightly to distinctly more posteriorly than upper labial extension. Interlabial membrane thin with slightly thicker longitudinal striations; ventral surface with small papillae in distal half; distal margin moderately wide (i.e., upper and lower labial extensions separated). Mental barbels profusely ornamented with fleshy papillae; outer pair finishing slightly posterior to inner pair. Basal portions of mental barbels united by thin membrane with thicker longitudinal striations and small fimbriae along distal margin. Dorsolabial membrane absent.

Anterior and posterior nares separated, openings surrounded by tube of skin; posterior wall of tube surrounding anterior naris slightly expanded as small flap; anterior wall of posterior naris also expanded as small flap. Anterior naris located between snout tip and posterior naris; posterior naris larger than anterior, much closer to anterior margin of orbit than to anterior naris.

First ceratobranchial with 16-21 short rakers (2-3 upper, 14-18 lower; n = 3, SL 73-122.5 mm); entire raker (i.e., ossified acicular portion and skin covering) narrowly subtriangular with transversely oriented base. Medial face of first ceratobranchial with thin, soft, and fleshy triangular lamellae ( Fig. 4 ). Lamellae arranged into distinctly spaced columns more or less perpendicular to axis of lower arch and loosely aligned with every second raker and every third gill filament. Lamellar columns extending from base of rakers onto basal third to half of filaments. Innermost lamella (nearest rakers) largest in each column; lamellae becoming gradually smaller outwardly. Outermost lamellae in each column conjoined and weakly adhered to gill filament (attachment easily broken, may be lost in adults). Bases of filaments skirted by thin membrane from which outermost lamellae originate. Branchiostegal membrane broadly united to isthmus; distal free portion narrowly expanded with fleshy margin.

Skin relatively smooth except for extremely minute punctate to dash-like tubercles most abundant on snout. Skin between axilla of pectoral fin and ventral margin of postcleithral process with multiple large pores in triangular patch tapering posteriorly, finishing short of ventral posterior corner of process.

Dorsal fin I,6; pectoral fin modally I,9*, range I,7-10; pelvic fin i,6; anal fin modally v,9, range iv-v,7-10 (holotype iv, 10); caudal fin i,7/8,i (erroneously reported as i,8/9,i for Leptodoras in Sabaj, 2005) with dorsal procurrent rays modally 16*, range 12-19, and ventral procurrent rays modally 15*, range 12-18 (n = 47 for all counts). Dorsal-fin origin located approximately one-third of SL from snout tip. Dorsalfin spine strong, compressed, gently curved over entire length and gradually tapered to sharply pointed ossified tip (dorsal-spine tip deformed in holotype); anterior margin weakly serrated along basal half (<110 mm SL) to two-thirds (> 120 mm SL), anterior serrations antrorse, crowded and acute basally, becoming gradually more spaced, less acute and anteriorly as fleshy keel; origin slightly posterior to anal-fin smaller distally; posterior margin weakly serrated along distal origin. Pectoral-fin spine strong, dorsoventrally flattened, two-thirds, posterior serrations weakly retrorse, similar in size gently curved over entire length and gradually tapered to to anterior ones but more spaced and becoming gradually sharply pointed ossified tip; length and shape similar to that smaller towards tip and towards base. Adipose fin tear-drop of dorsal spine; adpressed tip approximately reaching vertishaped with rounded free distal margin; base not continued cal through pelvic-fin origin; anterior margin moderately serrated for entire length or distalmost tip sometimes smooth,

Table 1. Morphometric data for Leptodoras oyakawai (Hol = anterior serrations antrorse becoming gradually larger towards holotype). midlength, then smaller and less acute towards tip; posterior margin with slightly larger retrorse serrations for entire length,

posterior serrations largest near midlength, becoming much smaller towards base and slightly smaller towards tip. Pelvic fins subtriangular, distal margin straight to weakly rounded and perpendicular to longitudinal axis when moderately extended; origin slightly posterior to posterior base of dorsal fin, and anterior to midpoint of SL in smaller specimens (<110 mm SL) becoming closer to midpoint in larger specimens (> 120 mm SL). Anal fin large, triangular with extended distal margin straight to weakly concave, angled ventroanteriorly. Caudal fin forked with lobes approximately equal; lobes weakly rounded in adults, more pointed in juveniles. Upper and lower procurrent caudal-fin rays like those of caudal fin, not modified into plates.

Lateral line ossified with complete series of 33 (1), 34 (6), 35 (36), 36* (21) or 37 (3) midlateral scutes per side, beginning with infranuchal. Sum of both sides: 67 (1), 68 (1), 69 (6), 70 (5), 71* (16), 72 (12), 73 (2) or 74 (2). Lateral line in tympanic region (delimited by infranuchal scute, nuchal shield and postcleithral process) with three separate ossifications de- creasing in size anteriorly to posteriorly, and largely covered by skin except for small emergent thorn; anteriormost ossification elongate and plate-like, posteriormost one highly reduced and sometimes lacking thorn. Infranuchal scute tall with well-developed laminar wings above and below medial ridge or weak thorn; anterior margin embedded in skin; posterior margin exposed, strongly serrated with deep central notch separating dorsal and ventral wings; dorsal wing firmly attached to posterior nuchal plate dorsally; ventral wing medially attached to first rib (borne on sixth vertebra) and underlying distal margin of postcleithral process anteroventrally ( Fig. 7b ). Postinfranuchal scutes oblique and strongly overlapping, depth uniform to anal-fin origin, then becoming gradually shallower to caudal-fin base; depth of scutes above pelvic-fin origin one-fourth to one-fifth of corresponding body depth. Each postinfranuchal scute with subtriangular dorsal and ventral wings above and below distinct medial thorn curved posteriorly; posterior margins of wings distinctly serrated; dorsal wing drawn out anterodorsally into point, ventral wing similarly drawn out posteroventrally. Infranuchal scute with dorsal wing weakly overlying that of first postinfranuchal scute.

Gas bladder moderately sized, occupying most of anterodorsal portion of visceral cavity; external wall (tunica externa) thin and smooth, without diverticula; internal Tshaped septum well-developed, completely divides posterior half into separate chambers which are partially separated from single anterior chamber ( Fig. 5 ). Gas bladder in juveniles much wider than long with broad anterior chamber (total width 1.6 and 1.7 times total length in specimens 89 mm and 50.3 mm SL, respectively; Figs. 5 a-b). In adults posterior chambers become relatively larger (total bladder width about equal to total length in specimen 121.7 mm SL) and together with broader anterior chamber impart acorn-like shape to entire bladder ( Fig. 5 c-f). Müllerian windows subcircular, deeply inserted on anterior wall of gas bladder, approaching vertical in transverse plane.

Osteology. Mesethmoid shaped like a fountain pen nib, very elongate (length about 7 times width), posterior sides more or less parallel to transverse line across anterior tips of nasal bones, anterior sides gradually converging to narrow tip with minute notch; posteriorly with V-shaped notch enclosing anterior cranial fontanel ( Fig. 7a ). Lateral ethmoid elongate; posterior half superficial, forming significant portion of anterior border of orbit; dorsomedially sutured to frontal and mesethmoid aside small intervening gap, and anteroventrally attached to first infraorbital (lacrimal). Nasal very thin, long, and unbranched. First infraorbital (lacrimal) elongate and not contributing to orbital perimeter ( Fig. 7b ); medial margin with broad concavity for anterior naris; anterior and posterior wings similarly sized or posterior wing slightly larger; both wings moderately long, pointed; posterior wing remote from orbit. Second, third and fourth infraorbitals canal-like, thin and long, completing ventral perimeter of orbit between first infraorbital and anterolateral corner of sphenotic; fourth infraorbital longest, L-shaped. Frontal elongate, narrow, completing dorsalmedial perimeter of orbit. Cranial fontanel long and very narrow, with anterior and posterior openings separated by epiphyseal bar slightly anterior to point where frontal-sphenotic suture meets orbital rim. Anterior cranial fontanel longer, length 2-3 times that of posterior fontanel, enclosed anteriorly by small Vshaped notch in mesethmoid and laterally by frontals; posterior fontanel narrowly triangular, pointed posteriorly, enclosed laterally by frontals and posteriorly by small notch in parieto-supraoccipital. Parieto-supraoccipital octagonal, slightly broader than long, surrounded by frontals, sphenotics, pterotics, epioccipitals, and anterior nuchal plate. Sphenotic subpentagonal with acute anterolateral corner attached to fourth infraorbital. Pterotic subpentagonal, posterior ventral margin sutured to posttemporal-supracleitrum. Epioccipital roughly quadrangular to pentagonal, with externally visible sutures to pterotic anteriorly, parieto-supraoccipital and sometimes anterior nuchal plate medially and middle nuchal plate posteriorly; suture to posttemporalsupracleitrum largely internal except for very short portion visible externally. Epioccipital posterior process well developed, ossified to posterior nuchal plate; laminar with lateral vertical portion curving smoothly and ventrally inwards as horizontal shelf; process relatively narrow anteriorly, becoming gradually expanded posteriorly, particularly in vertical plane. Anterior nuchal plate well developed, subpentagonal (pointed posteriorly), wider than long. Middle nuchal plate large, somewhat butterfly-shaped; lateral margins concave; anterior margin remote from parietosupraoccipital and with broad V-shaped notch for anterior nuchal plate. Posterior nuchal plate narrow, ventrally elongated to point near third tympanal ossification with ventral posterior margin attached to infranuchal scute; superficial portion ornamented as remaining nuchal shield. Nuchal shield roof-shaped, more so posteriorly (forming about 90° angle); with narrow medial groove in smaller specimens, becoming obsolete in adults. Nuchal foramina usually present; opening as long slit-like fissure between anterior nuchal plate and epioccipital that may be partially or completely occluded, replaced by suture between same bones in larger specimens (SL> 96 mm).

Cranium in ventral view with prevomer elongate, slightly expanded anteriorly but without distinct (acute) anterolateral processes. Parasphenoid narrow, distinctly elevated from skull roof (in ventral view) by interorbital septum formed in large part by adpressed orbitosphenoids. Basioccipital with short lateral arms firmly sutured to ossified transcapular (Baudelot’s) ligament. Ossified transcapular ligament flattened anteroposteriorly and broadly expanded ventrally; ventral margin rounded, entire except for transverse notch(es) in medial side, usually deep and narrow; sometimes with small foramina in center of ossified ligament.

Premaxilla edentulous, subtriangular, with medial margin attached to ventral keel of mesethmoid by connective tissue, and lateral point expanded by elongate rod of cartilage or connective tissue contributing to oral hood. Maxilla elongate and curved, proximal end bifurcated into two condylar processes articulating with complex facet formed by mesethmoid, premaxilla and cartilaginous head of autopalatine. Autopalatine long, rod-like; central portion narrow with weak process for articulation with shallow cartilaginous facet formed by first infraorbital, mesethmoid and lateral ethmoid; bone becoming gradually larger towards either end both of which are capped with cartilage. Dentary edentulous, elongate, posteriorly sutured to anguloarticular ( Fig. 8 ); anterior portion tooth-brush-like, posterior portion trapezoidal. Remnant of Meckelian cartilage L-shaped with vertical arm forming cartilaginous coronoid process. Quadrate relatively broad, anteriorly with condylar region for articulation with lower jaw; joined ventrally to preopercle, anterodorsally to metapterygoid and posterodorsally to hyomandibula via cartilage. Metapterygoid small, triangular with anterior and dorsal sides enclosed by mesopterygoid. Mesopterygoid larger, contacting lateral ethmoid. Hyomandibula elongate, relatively narrow and gently curved for entire length, lacking contact anteriorly with metapterygoid. Preopercle long and very narrow, dorsal margin attached quadrate (anteriorly) and hyomandibula (posteriorly). Interopercle relatively large, roughly trapezoidal. Opercle roughly triangular, firmly attached by connective tissue to lateral border of pterotic.

Urohyal small ( Fig. 9 ), with well-developed ventral process. Ventral hypohyal large, joined to anterior ceratohyal via cartilage and short suture; dorsal hypohyal much smaller, arched. Small fenestra enclosed by ventral hypohyal anteriorly and dorsal hypohyal posteriorly.Anterior ceratohyal large, expanded posteriorly, and joined to posterior ceratohyal via cartilage. Seven branchiostegal rays, five attached to anterior ceratohyal and two to interceratohyal cartilage.

Five branchial arches ( Fig. 10 ). Three basibranchials (first one absent); basibranchials two and three elongate, ossified with cartilaginous caps; fourth one longest, cartilaginous. Three hypobranchials; first and second ones elongate, ossified with cartilaginous caps; third one short and broad, cartilaginous, medially attached between basibranchials three and four. Five ceratobranchials; first four narrow, elongate, ossified with cartilaginous caps; dorsal half of cartilaginous cap of fourth ceratobranchial expanded anteriorly as narrow process aside fourth basibranchial; fifth ceratobranchial with extremely narrow proximal stalk and triangularly expanded distal portion bearing single medial row of about 10 acicular teeth. Five epibranchials; first four elongate, ossified with cartilaginous caps; third one with small posterior process; fifth one small, rod-like, cartilaginous. Three pharyngobranchials; first one small, rectangular, cartilaginous, connected to first two epibranchials and second pharyngobranchial; second pharyngobranchial elongate, ossified with cartilaginous caps; third pharyngobranchial small, ossified portion semicircular with rounded margin capped in cartilage, connected to second pharyngobranchial and third and fourth epibranchials and supporting elongate, lenticular plate with many long acicular teeth.

Pectoral girdle in ventral view subtriangular, elongated anteriorly with broad (obtusely) pointed tip; lateral (convergent) margins shallowly concave ( Fig. 11 ). Coracoid posterior process short, barely surpassing posterior base of pectoral fin. Ventral surfaces of pectoral girdle, including posterior processes of coracoid, concealed by skin (not visible externally). Abductors superficialis and arrector ventralis muscles separated by oblique bony crest on ventral surface of coracoid; crest oriented about 45° from longitudinal.

Postcleithral process moderately elongate, obliquely truncated posteriorly; dorsal margin shallowly concave opposite posttemporal-supracleithrum, then more or less straight for short distance before curving ventrally to distinct posteroventral corner; ventral margin straight. Surface ornamented with fine, longitudinal ridges becoming more broken and sometimes loosely reticulated posteriorly; ornamentation sometimes separable into two longitudinal fields (wide dorsal and narrow ventral) by continuous subventral ridge. Entire postcleithral process laterally compressed, thickness nearly uniform (i.e., blade-like), without distinct longitudinal swelling or thickening along medial face.

Basipterygium of pelvic girdle subtriangular with four processes: two anterior, one lateral and one posterior ( Fig. 12 ). Anterior processes long and thin, ossified with cartilaginous caps; lateral (outer) one paralleling longitudinal body axis, slightly longer and more robust than medial (inner) anterior process, and with small hook-like keel on dorsal surface near base; inner anterior process oblique, convergent but separate with pair, oriented about 30° from outer process. Lateral process small, pointed anteriorly, extending short distance beyond fin-ray insertions and capped in cartilage along lateral margin. Posterior process short and broad (trapezoidal) with obliquely truncated posterior margin; largely ossified except for cartilaginous cap along medial and posterior margins.

Total vertebrae 38 (2) or 40 (1) with compound caudal centra (PU1 + U1) counted as one and complex vertebra (2-4) completely fused to fifth vertebra, partially fused to sixth, and weakly incorporating seventh (i.e., intervertebral disk between sixth and seventh vertebrae reduced, obscured by ventral superficial ossifications); first normal intervertebral joint between seventh and eighth vertebrae. Complex vertebra (2-4), and perhaps first vertebra, covered ventrally and laterally by superficial ossifications completely enclosing aortic passage and with paired laminar expansions. Anterior portion of lamina nearly vertical and transversely aligned, cup-shaped with concave surface completing anterior wall of gas bladder (between Müllerian windows), and separated from its pair by triangular longitudinal keel. Posteriorly lamina becoming more horizontal, planar and obliquely oriented in transverse plane, expanded from dorsal portion of complex centrum, and completing tunica externa of gas bladder dorsomedially between left and right halves of anterior chamber. Fourth vertebra supporting relatively small, elongate Müllerian ramus, without distal disk-like expansion, but with prominent cartilaginous cap. Fifth vertebra with slender parapophysis directed posteriorly. Sixth vertebrae bearing first pair of ribs joined laterally to medial face of infranuchal scute. Ribs 6 (1) or 7 (2), borne on successive vertebrae. Caudal skeleton with parhypural partially fused to hypural 1 + 2 (first and second hypurals completely fused); two separate dorsal hypurals, 3 + 4 (fused) and 5, the latter closely associated with urostyle.

Coloration. Ground color tan on dorsal half of head and body. Ground color of lower sides and ventral surfaces pale white with faint dusky gray swath below scutes attenuated posteriorly above anal fin. Faint wide dusky gray stripe above midlateral thorns from infranuchal scute to caudal fin and confluent with its pair dorsally across caudal peduncle; faint broad dusky gray middorsal stripe from dorsal to adipose fins; pale white midlateral stripe along thorns and ventral wings of scutes from infranuchal onto caudal fin. Paired and anal fins pale except for some scattered dark pigment on anteriormost rays and membranes of pectoral fins. Adipose fin with dusky gray base and narrow pale margin. Caudal fin with two dark longitudinal stripes, one on each lobe, narrowly separated by pale midlateral stripe. Dorsal fin pigmentation variable. Jamanxim specimens (middle Tapajós, type series) with distinct dusky black triangular blotch on base of dorsal fin ( Fig. 2a ). Specimens from the rio Teles Pires (upper Tapajós) and upper Xingu with dark pigment largely limited to proximal third of anterior margin of dorsalfin spine, and with triangular basal blotch narrower, more faint or sometimes absent from remaining fin; in same specimens the dusky middorsal stripe is more faint or absent ( Fig. 2b ). Live coloration similar to above except dusky stripes less evident; ground color tinted olive; and longitudinal iridescences evident above midlateral scutes from infranuchal to below adipose fin in specimen from upper Xingu ( Fig. 2b ).

Distribution and Habitat. Leptodoras oyakawai is known from rio Jamanxim (type series) and rio Teles Pires, rio Tapajós basin, and rio Culuene and rio Curisevo, upper rio Xingu basin ( Fig. 13 ). Nearly all specimens were collected during the dry season when water levels were lowest (late September to October). Jamanxim specimens were collected at night on a large sandy shoal where the main channel was wide and shallow (depth less than 2 m) and current sluggish. The rio Culuene and rio Teles Pires specimens were collected at night along a sandy beach aside the main channel in moderate current.

Etymology. Named in honor of Osvaldo Takeshi Oyakawa, for his dedicated service to the ichthyological community since 7 July 1989 as Collection Manager of the Fish Collection (“Seção de Peixes”) at the Museu de Zoologia da Universidade de São Paulo.

Figures

Fig. 1. Leptodoras oyakawai, MZUSP 97909, holotype, 120.5 mm SL, in (a) lateral, (b) dorsal and (c) ventral views. Brazil, Pará, Novo Progresso, rio Jamanxim (Tapajós basin), at Prainha, near Novo Progresso.

Fig. 2. Leptodoras oyakawai in lateral view: (a) MZUSP 97395, paratype, 222.4 mm SL, rio Jamanxim, Tapajós basin, photographed immediately after preservation (right side of body), (b) MZUSP 91979, 108.7 mm SL, rio Culuene, upper Xingu basin, photographed live (left side of body).

Fig. 3. Mouth, barbels and lips of Leptodoras oyakawai, MZUSP 97909, holotype, 120.5 mm SL, in ventral view. Scale bar 5 mm.

Fig. 4. First gill arch of Leptodoras oyakawai, MZUSP 97395, paratype, showing accessory lamellae, in (a) lateral and (b) medial views. Scale bar 5 mm.

Fig. 5. Gas bladder of Leptodoras oyakawai, MZUSP 87028, 54 mm SL in (a) ventral and (b) dorsal views; MZUSP 95722, 88 mm SL in (c) ventral and (d) dorsal views; MZUSP 97395, 121.9 mm SLin (e) ventral and (f) dorsal views.Scale bar 5 mm.

Fig. 6. Anteriormost vertebrae, in ventral view, showing the bony capsules (arrows) of (a) Anduzedoras oxyhynchus, ANSP178551, 138 mm SL, and (b) Leptodoras cataniai,ANSP 179242, 157 mm SL, and cup-like expansions in (c) Leptodoras oyawakai,ANSP 187336, 120 mm SL. Scale bar 5 mm.

Fig. 7. Head of Leptodoras oyakawai, ANSP 187336, paratype, 120 mm SL, in (a) dorsal and (b) lateral (left side) views. acf anterior cranial fontanel, ANP anterior nuchal plate, CLE-pp postcleithral process, DEN dentary, EPO epioccipital, EPO-p epioccipital posterior process, FRO frontal, INS infranuchal scute, IO1-4 infraorbitals, LET lateral ethmoid, MAX maxilla, MET mesethmoid, MNP middle nuchal plate, NAS nasal, nf nuchal foramina, OPE opercle, pcf posterior cranial fontanel, PNP posterior nuchal plate, PAL autopalatine, PTO pterotic, SOC parieto-supraoccipital, SCL posttemporal-supracleithrum, SPO sphenotic, TyS tympanal scutes. Scale bar 5 mm.

Fig. 8. Suspensorial and opercle series in Leptodoras oyakawai, based on MZUSP 95722, 73 mm SL, in lateral view. AAR anguloarticular, DEN dentary, HYO hyomandibula, IOP interopercle, MSP mesopterygoid, MTP metapterygoid, OPE opercle, POP preopercle, QUA quadrate. Scale bar 5 mm.

Fig. 9. Hyoid arch of Leptodoras oyakawai, based on MZUSP 95722, 73 mm SL, in ventral view.ACH anterior ceratohyal, BRR branchiostegal rays, DHH dorsal hypohyal, ICH interceratohyal cartilage, PCH posterior ceratohyal, UHY urohyal, VHH ventral hypohyal. Scale bar 5 mm.

Fig. 10. Branchial skeleton of Leptodoras oyakawai, based on MZUSP 95722, 73 mm SL, in dorsal view. BB2-4 basibranchials, CB1-5 ceratobranchials, EB1-5 epibranchials, HB1-3 hypobranchials, PB2-4 pharingobranchials, TPL tooth plate. Scale bar 5 mm.

Fig. 11. Pectoral girdle of Leptodoras oyakawai, MZUSP 95722, 73 mm SL, in ventral view. CLE cleithrum, COR coracoid, COR-pp coracoid posterior process. Scale bar 5 mm.

Fig. 12. Pelvic girdle of Leptodoras oyakawai, based on MZUSP 95722, 73 mm SL, in dorsal view.BPT basipterygium, eap external anterior process of BPT, iap internal anterior process of BPT, lp lateral process of BPT, PFR pelvic-fin rays, pp posterior process of BPT. Scale bar 5 mm.

Fig. 13. Distribution of Leptodoras oyakawai in Tapajós and Xingu basins, central Brazil (type locality represented by open circle).