Potamotrygon falkneri Castex & Maciel, 1963

da Silva, João Paulo C. B. & de Carvalho, Marcelo R., 2011, A taxonomic and morphological redescription of Potamotrygon falkneri Castex & Maciel, 1963 (Chondrichthyes: Myliobatiformes: Potamotrygonidae), Neotropical Ichthyology 9 (1), pp. 209-232 : 211-222

Potamotrygon falkneri Castex & Maciel, 1963

Figs. 1-11

Potamotrygon vistrix ( lapsus for histrix ): Castex, 1963a:52, fig.10 (misidentification).

Potamotrygon histrix: Castex, 1963a:54 , 119 (misidentification).

Potamotrygon falkneri Castex & Maciel in Castex, 1963b:56- 61, figs. 16-17 (original description, río Paraná, Santa Fé, Argentina); Castex, 1964:31 (revision); Castex, 1965:45 ( allotype [ sic] description); Castex, 1967a:487-489 (dermal denticles of Potamotrygon species); Castex, 1967b:493, 495 (teeth of Potamotrygon species); Achenbach, 1971:2, 3, 6, 7, 8 (cited); Achenbach & Achenbach, 1976:4, 28 (cited); Rosa, 1985:175-192, figs. 45-49 (revision, redescription, figured); Taniuchi & Ishihara, 1990:15 (anatomical comparison of claspers); Compagno & Cook, 1995:67, 72, 73, 80 (listed); Ishihara & Taniuchi, 1995:91, 95, 97 (listed); Gómez & Chebez, 1996:46 (listed); Britski et al., 1999:21 (brief account, illustrated); Compagno, 1999:495 (listed); Marques, 2000:42, 55, 107, 162, 163, 166, 167, 169 (helminth parasites); Bor, 2002:30 (listed); Carvalho et al., 2003:24 (accepted as valid, taxonomic account); López et al., 2003:6 (listed); Marques et al., 2003:368, 371, 373-375 (cited); Carvalho et al., 2004:10, 61, 93 (anatomical account); Menni, 2004:70 (cited); Compagno, 2005:540 (listed); López et al., 2005:314, 324 (listed); Deynat, 2006:491 (cited); Lonardoni et al., 2006:195-200, 202 (ecological study, upper rio Paraná); Rosa & Carvalho, 2007:17 (listed); Garrone Neto et al., 2007:206, 207 (biological study, upper rio Paraná); Graça & Pavanelli, 2007:22, 23 (brief account, upper rio Paraná); Silva & Uieda, 2007:221-226 (biological study, upper rio Paraná).

Potamotrygon menchacai Achenbach, 1967:1-8 (original description, río Colastiné, Santa Fé, Argentina); Castex, 1967a:485, 487, 488 (dermal denticles of Potamotrygon species); Castex, 1967b:493 (teeth of Potamotrygon species); Achenbach, 1971:2-7 (cited); Achenbach & Achenbach, 1976:4, 28 (cited); Rosa, 1985:175-177 (cited as a synonym of P. falkneri ); Carvalho, 2001:1168 (cited); Carvalho et al., 2003:24 (in synonymy of P. falkneri ); Velte, 2005:53 (cited).

Potamotrygon castexi Castello & Yagolkowski, 1969:1-21 (original description, río Paraná, Rosário, Argentina); Achenbach & Achenbach, 1976:4, 28 (cited); Rosa, 1985:126-140, figs. 31-34 (accepted as valid; redescription); Ortega & Vari, 1986:6 (listed); Nishida, 1990:58, 62, 90, 92, 94 (anatomical description); Compagno & Cook, 1995:67, 72, 73, 80, 81 (listed); Deynat & Séret, 1996:81 (dermal denticles); Compagno, 1999:495 (listed); Bor, 2002:30 (listed); Carvalho et al., 2003:24 (accepted as valid, taxonomic account); López et al., 2003:6 (listed); Menni, 2004:70 (listed); Compagno, 2005:540 (listed); Deynat, 2006:491 (cited); Rosa & Carvalho, 2007:17 (listed). [NEW SYNONYM].

Material examined. ( 83 specimens). ANSP 142482 ( male, 429 mm DW), río Manu below Boca Pinquen, Gomero, Peru, 12º11’S 70º58’W, 10 Aug 1977; ANSP 142483 ( male, 265 mm DW), same data as ANSP 142482; ANSP 142484 ( male, 374 mm DW), tributary on SW bank of río Manu , 7 km below Boca Pinquen, Peru, 12º12’S 70º59’W, 11 Aug 1977; ANSP 142486 ( male, 386 mm DW), same data as ANSP 142482; ANSP 142487 ( female, 406 mm DW), same data as ANSP 142484; FMNH 84091 ( male, 354 mm DW), río San Alejandro , near Puerto Nuevo, río Pachitea drainage , Peru; LACM 39934-1 ( female, 286 mm DW), río Yutupis , Shiringa, Amazonas, Peru; LACM 39942-1 ( male, 432 mm DW), same data as LACM 39934-1; LACM 41772-2 ( male, 225 mm DW), río Santiago , small “quebrada” across from La Poza, Amazonas, Peru; MACN 2732 ( female neonate, 110 mm DW), riacho Formosa , rio Paraguai affluent, Brazil; MACN 9092 ( male, 578 mm DL; disc damaged), río Colastiné Sul , Província de Santa Fé, Argentina; MACN 9093 ( male, 476 mm DW), same data as MACN 9092; MFA 73 ( female, 351 mm DW), riacho Santa Fé , Província de Santa Fé, Argentina, 24 Apr 1951 ; MFA 235 ( female, 286 mm DL; disc damaged), río Paraná , Província de Santa Fé, Argentina, Paratype of Potamotrygon falkneri Castex & Maciel, 1963 , coll. Castex & Maciel, June 1963 (fig. 2a-c) ; MZUSP 106255 ( female, 279 mm DW), rio Paraná , Paraná basin , municipal district of Jupiá, Três Lagoas, State of Mato Grosso do Sul, Brazil, 20º47’24”S 51º39’W, 15 Dec 2003 ; MZUSP 106256 ( female, 338 mm DW), same data as MZUSP 106255; MZUSP 106257 ( female, 275 mm DW), same data as MZUSP 106255; MZUSP 106268 ( male, 305 mm DW), same data as MZUSP 106255; MZUSP 106269 ( female, 264 mm DW), same data as MZUSP 106255; MZUSP 106258 ( female, 292 mm DW), same data as MZUSP 106255; MZUSP 106270 ( female, 372 mm DW), same data as MZUSP 106255; MZUSP 106259 ( female, 292 mm DW), same data as MZUSP 106255; MZUSP 106271 ( male, 286 mm DW), same data as MZUSP 106255; MZUSP 106260 ( female, 322 mm DW), same data as MZUSP 106255; MZUSP 106266 ( female, 490 mm DW), same data as MZUSP 106255; MZUSP 106267 ( female, 518 mm DW), same data as MZUSP 106255; MZUSP 106261 ( female, 280 mm DW), same data as MZUSP 106255; MZUSP 106262 ( male, 273 mm DW), same data as MZUSP 106255; MZUSP 106263 ( female, 256 mm DW), same data as MZUSP 106255; MZUSP 106265 ( male, 231 mm DW), same data as MZUSP 106255; MZUSP 14578 ( female , 388 mm DW), rio Piquiri , Paraguai basin , Brazil, 17º12’S 54º09’W, Oct 1978 ; MZUSP 14848 (male, 420 mm DW), Taiamã’s Reservatory , rio Paraguai , Brazil, 15º10’59”S 56º24’W, 8 Aug 1980 ; MZUSP 14852 ( male, 371 mm DW), Fazenda Descalvados , rio Paraguai , Brazil, 16º44’S 57º45’W, 8 Sep 1980 ; MZUSP 81089 ( female, 435 mm DW), same data as MZUSP 106255; MZUSP 81090 ( female, 355 mm DW), same data as MZUSP 106255; MZUSP 81091 ( male, 310 mm DW), same data as MZUSP 106255; MZUSP 81092 ( female , 385 mm DW), same data as MZUSP 106255; MZUSP 81093 ( female, 370 mm DW), same data as MZUSP 106255; MZUSP 81094 ( female, 352 mm DW), same data as MZUSP 106255; MZUSP 81095 ( female, 398 mm DW), same data as MZUSP 106255; MZUSP 107667 ( male, 362 mm DW), río Madre de Díos , municipal district of Boca Manu, upper Amazon basin , State of Madre de Díos, Peru, 12º40’S 71º04’06”W, May 2001 ; MZUSP 107668 ( female, 265 mm DW), same data as MZUSP 107667; MZUSP 107669 ( male, 293 mm DW), same data as MZUSP 107667; MZUSP 107670 ( male, 300 mm DW), same data as MZUSP 107667; MZUSP 107671 ( male, 351 mm DW), same data as MZUSP 107667; MZUSP 107672 ( male, 291 mm DW), same data as MZUSP 107667; MZUSP 107673 ( male, 348 mm DW), same data as MZUSP 107667; MZUSP 108680 ( female, 350 mm DW), rio Casca , upper rio Paraguai basin , municipal district of Chapada dos Guimarães, state of Mato Grosso, Brazil, 15 o 01’S, 55 o 32’W, 17 Apr 2000 ; MZUSP 108681 ( male, 350 mm DW), rio Manso , upper rio Paraguai basin , municipal district of Nobres, boundary with Rosário Oeste, state of Mato Grosso, Brazil, 20 Mar 2000 ; MZUSP 108682 (neonate, 161 mm DW), rio Aricá Mirim , rio Cuiabá affluent, rio Paraguai basin , state of Mato Grosso, Brazil; MZUSP 108683 ( male, 365 mm DW), rio Cuiabá , upper rio Paraguai basin , municipal district of Nobres, boundary with Rosário Oeste, state of Mato Grosso, Brazil, 17 Jun 2000 ; NUP 2107 ( male, 280 mm DW), rio Cuiabazinho , affluent of rio Cuiabá , state of Mato Grosso, Brazil; NUP 2917 ( female, 325 mm DW), same data as MZUSP 108681; NUP 2922 ( female , 501 mm DW), same data as MZUSP 108682; NUP 2923 ( male, 380 mm DW), same data as NUP 2107; NUP 2945 ( female, 403 mm DW), same data as MZUSP 108683; NUP 2968 ( male, 235 mm DW), affluent of rio Cuiabá , bahia Sinhá Mariana, rio Paraguai basin , state of Mato Grosso, Brazil; NUP 3016 ( male, 257 mm DW), rio Casca , upper rio Paraguai basin , municipal district of Chapada dos Guimarães, state of Mato Grosso, Brazil, 15 o 01’S, 55 o 32’W, 17 Aug 2003 ; NUP 3220 ( female, 230 mm DW), rio Manso , rio Cuiabá affluent, rio Paraguai basin , state of Mato Grosso, Brazil; MZUSP 108684 ( female, 325 mm DW), rio Paraná , 1 km below rio Baía estuary , upper rio Paraná basin , municipal district of Taquarussu, state of Mato Grosso do Sul, Brazil, 22 o 45’S, 53 o 20’W, 10-23 Mar 2004 ; MZUSP 108685 ( female, 299 mm DW), same data as MZUSP 108684; MZUSP 108686 ( male, 351 mm DW), same data as MZUSP 108684; MZUSP 108687 ( male, 366 mm DW), same data as MZUSP 108684; MZUSP 108688 ( male, 238 mm DW), same data as MZUSP 108684; MZUSP 108689 ( female, 337 mm DW), same data as MZUSP 108684; MZUSP 108690 ( female, 311 mm DW), same data as MZUSP 108684; MZUSP 108691 ( female, 358 mm DW), same data as MZUSP 108684; MZUSP 108692 ( male, 330 mm DW), same data as MZUSP 108684; MZUSP 108693 ( female, 410 mm DW), same data as MZUSP 108684; MZUSP 108694 ( male, 391 mm DW), same data as MZUSP 108684; MZUSP 108695 ( male, 342 mm DW), same data as MZUSP 108684; MZUSP 108696 ( male, 313 mm DW), same data as MZUSP 108684; MZUSP 108697 ( male, 238 mm DW), same data as MZUSP 108684; MZUSP 108698 ( male, 281 mm DW), same data as MZUSP 108684; MZUSP 108699 ( male , 240 mm DW), same data as MZUSP 108684; MZUSP 108700 ( male, 248 mm DW), same data as MZUSP 108684; MZUSP 108701 ( male, 273 mm DW), same data as MZUSP 108684; MZUSP 108702 ( female, 311 mm DW), same data as MZUSP 108684; MZUSP 108703 ( female, 245 mm DW), same data as MZUSP 108684; MZUSP 108704 ( male, 265 mm DW), same data as MZUSP 108684; MZUSP 108705 ( male, 311 mm DW), same data as MZUSP 108684; UMMZ 204551 ( female, 366 mm DW), río Itenez , 9 km southwest of Costa Marques, state of Rondônia, Brazil, 12 o 32.4’S, 64 o 16.6’W, 18 Sep 1964 .

Diagnosis. A species of Potamotrygon distinguished from congeners by the following combination of characters: dorsal disc with dark brown background coloration, with circular, reniform, oval, vermicular and/or rosette-like beige and orange spots, equal to or smaller than eye diameter; presence of one to three midrow of irregular spines on dorsal tail; presence of star-shaped, asymmetrical and minute dermal denticles, frequently with crown dichotomies, concentrated in central region of disc. In relation to congeners in the Paraná-Paraguay basin, P. falkneri is further distinguished from P. motoro by lacking on disc ocelli formed by strong black concentric rings, by the more flattened aspect of its disc, by presenting much smaller dermal denticles, and by having a greater number of tooth rows in upper jaw (30-45 vs. 23-32, respectively). From P. brachyura , P. falkneri is further distinguished by presenting a proportionally much longer tail (mean values 55% vs. 87.9% of DW, respectively), and in lacking a dorsal reticulate pattern. From P. histrix , P. falkneri is further separated by not presenting a dark grey dorsal and ventral disc, by having a slightly higher number of total vertebrae (means values 127 vs. 123, respectively), and by lacking developed dermal denticles on disc and tail margins. Potamotrygon falkneri is distinguished from the highly similar form recognized below as Potamotrygon sp. by not presenting its elongated distal tail extension posterior to sting, by having tail spines in one to three irregular rows (instead of a unique row), greater total pectoral radials (94- 100 vs. 90-93), and spots that are not exclusively vermicular.

Description. Morphometric and meristic data are shown in Tables 1-3 .

External morphology. Disc oval ( Figs. 1 and 2 ), only slightly longer than wide (DL 102.1-114.7% of DW). Anterior margin of disc convex, with a small fleshy protuberance on snout. Posterior margins of disc also convex, their inner margins fused posteriorly to the dorsal surface of pelvic fins and tail base. Disc dorsoventrally compressed, relatively slender. Anterior portion of disc with small, prominent, and oval shaped eyes. Spiracles oval and small (1.5 to 3 times eyes diameter) situated posterior to orbits and projecting obliquely from midline. Interspiracular distance greater (aproximately 1.5 times) than interorbital distance. Nasal curtain partially covering mouth and presenting small, fringed posterior ramifications. Mouth small (width 6.8-10.9% DW); mouth opening relatively straight across and with five buccal papillae, two lateral and three central. One of three central papillae closer to lower jaw tooth plate. Mouth width and internarial space about equal. Labial ridges present. Teeth set in quincunx, with narrow and arched upper tooth plate, and wide and trapezoidal lower tooth plate. Tooth rows varying from 30-45 on upper jaw and 29-43 on lower jaw. Teeth relatively small, wider than long, and with flattened, elliptical, or lozenge-shaped crowns. Cusps rounded, pointed in males, or absent. Tooth plates presenting dignathic heterodonty. Teeth in lateral rows with elliptical crowns and generally lacking cusps. Teeth in central rows more robust, with lozenge-shaped crowns and rounded cusps. Sexual dimorphism present; some mature males with pointed cusps centrally on both tooth plates or on lower tooth plate only. Roots bilobed (holaulacorhize), with lobes separated by a shallow basal median groove.

Branchial basket relatively narrow and short, with space between first branchial slits 21.4-26.1% of DW and distance between first and last branchial slits 14.2-17.6% of DW. Pelvic fin wider than long, partially covered by disc, and with posterior margin dorsally exposed posterior to disc margin. Anterior margin of pelvic fin oblique in relation to midline. Clasper dorsoventrally depressed, wider at bases and narrowing distally, with rounded tips. Clasper groove beginning proximally at level of posterior margin of pelvics. Anterior half of clasper groove running obliquely from inner margin to outer margin of clasper. Posterior half curving inward at level of pseudosiphon, reaching midline and extending to clasper tip. Dorsal pseudosiphon well developed near inner edge, elliptical, and obliquely oriented in relation to midline. Ventral pseudosiphon also well developed, located at lateral distal edge of clasper.

Tail moderately elongated (tail length 87.9% of DW) and wide (mean width 13.3% of DW), with proximal portion slightly depressed dorsoventrally, and tapering from base to just posterior to sting insertion. Distal portion of tail, posterior to sting base, laterally compressed and presenting membranous dorsal and ventral caudal folds (these about 3-4 mm in height). Dorsal caudal fold originating underneath sting tip and extending to tail extremity. Ventral caudal fold originating at level ventral to sting base, extending to tail extremity. Serrated sting on dorsal tail single or paired, and relatively elongated (15.8-25.5% of DW). Irregular midrows of spines on tail varying from one to three rows, and extending from base of tail to level of sting insertion. Enlarged spines on tail with rounded bases.

Dermal denticles. Males and females with similar dermal denticle morphology and distribution ( Fig. 3 ). Disc with dermal denticles evenly scattered on midregion, from interorbital area to tail base. Denticles centrally positioned on disc with predominantly four to five crown ridges (cr), but varying from four to seven ridges. Crown ridges frequently showing crown dichotomies (cd). In dorsal view, denticles asymmetrical and star-shaped due to different lengths of crown ridges. Minute dermal denticles interspersed with larger denticles, exhibiting two to four crown ridges. Denticles in central region with rounded crown plates (cp).

Denticles more dispersed and smaller farther away from central region of disc, with crown ridges becoming less evident. Denticles on disc margins very rare, almost indiscernible. Dermal denticles also occur around and on margins of spiracle openings, as well as on orbits. Denticles devoid of crown ridges, but with pointed crowns, occur exclusively on spiracle superior margins, whereas denticles with two crown ridges and rounded crown plates occur on remaining regions. Pelvic fins and claspers devoid of dermal denticles. Denticles on dorsal tail small, devoid of crown ridges and with crowns sharply pointed, accompanying spine rows. Dorsal caudal fold presenting numerous very small dermal denticles; ventral caudal fold devoid of dermal denticles. Dermal denticles also occur on lateral tail region, from slightly anterior to sting base to distal tail extremity. Denticles more developed near sting base, becoming smaller closer to tail tip.

Coloration. Dorsal disc coloration variable ( Figs. 1 and 2 ). Disc background color generally dark brown, but some specimens black or grey. Spots on background presenting circular, reniform, and oval shapes, with diameter equal to or smaller than eye diameter. Vermiculations and rosettes also present in some specimens. Spots varying in distribution and proximity dorsally on disc. Circular and reniform spots predominant but variable combinations also occur. In some specimens, vermiculations occur exclusively, and close together. Larger (older) specimens present very sparse reniform and rosette-like spots ( Fig. 1N ). Spots beige, light beige, brown, or orange. In specimens with dark brown or dark grey background, spots may be contoured by a fine dark band, resembling faint, irregular ocelli. In addition, small circular spots on disc edges present in most specimens. Pelvic fins dorsally similar to disc. Tail also with same basic color pattern, but usually with more vermiculations and rosettes.

Ventral medial region of disc white to off-white in majority of specimens. Within white background, small, rounded grey spots occur laterally and posterolaterally to gill slits. These spots are found scattered anteriorly, and coalesce posterioly. In some specimens, rounded and scattered grey spots also occur within the space between branchial slits. Border of disc margins grey, from level of nasal slits to posterior region of disc. Some specimens predominantly grey ventrally, with white embracing only a small portion of anterior region (larger specimens also present this pattern of ventral coloration, Fig. 1O ). In these specimens, branchial slits surrounded by grey coloration. Light grey and white circular to vermicular spots may occur over grey background. Some specimens present variation in spot diameter, from bigger spots at margins to smaller spots on disc center, while others present spots of same size. In some cases, in region posterior to branchial slits, a black oval spot occurs of varying shape and intensity. Pelvic fins with predominantly dark grey ventral coloration, presenting small circular, reniform and vermicular white spots. White coloration restricted to fine bands on anterior region of fins. Cloaca surrounded by white coloration. Ventral tail region with a disorganized reticulated pattern, formed by irregular light grey and white vermicular spots, over a grey background. Distal extremity of tail black, with small, irregular white spots.

Sensory canal system. Particular characteristics of ventral lateral-line canals in Potamotrygon falkneri include ( Fig. 4 ): suborbital loop (sol), originated from the infraorbital canal (ioc), far from hyomandibular canal (hyoc) anteriorly, and projecting towards middle portion of disc; presence of an elevated number of anterior subpleural tubules (ast) projecting from hyomandibular canal on anterior-most part of the disc; hyomandibular jugular component (hjc) extends laterally to the branchial slits, lightly undulated; the jugular canal (jug) presents pronounced undulations adjacent to the branchial slits; hyomandibular subpleural component (hsc), extends laterally to the disc margins, devoid of any evident undulation; mandibular canal (man) short, situated posterior to mouth, extending posterolateraly and with pronounced undulations on its proximal portion; infraorbital loop (iol) with tenuous undulations at its internal corners; orbitonasal component of supraorbital canal (ocs) rather homogeneous; final ascendant part of suborbital component (sci) originates from infraorbital canal highly undulated; prenasal loop (pnl) short and straight; posterior subpleural tubule (pst) usually single and projecting obliquely from subpleural loop (spl) to posterolateral margin of disc. Some specimens present both orbitonasal component of supraorbital canal and final ascendant part of suborbital component of infraorbital canal, slightly undulated.

Neurocranium. Neurocranium somewhat elongated ( Fig. 5 ), with elliptic and ventrolaterally expanded nasal capsules (nc). Anterior margins of nasal capsules convex, presenting a medial notch in between. An internal, ventromedial sept divides the nasal capsules. Preorbital processes (prp) well developed and curved backwards, situated above the condyle for the antorbital cartilage. Postorbital processes (pop) shelf-like, anterolaterally expanded and located on dorsolateral corners of otic region. Supraorbital processes (sp) small and triangular, situated slightly anterior to postorbital processes. Supraorbital crests (soc) originating posteriorly to preorbital processes and extending posteriorly to postorbital processes. Antorbital cartilage condyles (anc) on posterolateral extremities of nasal capsules. Precerebral fontanelle (pcf) and frontoparietal fontanelle (fpf) partially separated by a moderately developed transverse bridge, the epiphysial bar. Together, fontanellae keyhole shaped, circular anteriorly and narrowing posteriorly. Hyomandibular facet (hmdf) located on ventrolateral corner of otic region and corresponds to an oval, horizontally positioned depression. Dorsally, neurocranium presents anterior foramen for preorbital canal (afpc) at base of preorbital process, and several foramina for the superficial ophthalmic nerve (sup) piercing supraorbital crest. Paired internal carotid artery foramina (icaf) ventrally situated near lateral edges of neurocranium. Eye-stalk (es) origin oval, originating on lateral orbital wall just posterior to wide and oval optic nerve foramen (II). Oculomotor nerve foramen (III) dorsal to eyestalk. A bridge-like lateral commisure (lc) present external to hyomandibular branch of facial nerve foramen (VII). Posterior foramen for preorbital canal (pfpc) also located dorsally, at junction of nasal capsule and orbit. Anterior cerebral vein foramen (acvf) located anterodorsal to optic nerve foramen. The efferent spiracular artery foramen (esaf) posteroventral to eye-stalk. Interorbital vein foramen (ivf) positioned posterior to base of eye-stalk. Relatively wide orbital fissure (obf) located above and slightly anterior to hyomandibular branch of facial nerve foramen. Foramen magnum (fm) circular. Articular surface (as) and occipital condyles (oc) for articulation with synarcual ventral to foramen magnum. Vagus nerve foramen (X) situated laterally to foramen magnum; glossopharyngeal nerve foramen (IX) located dorsolaterally in relation to occipital condyles. Two pairs of lymphatic foramina present dorsally in otic region, the anterior endolymphatic foramen (elf) and posterior perilymphatic foramen (plf).

Hyomandibular arch. Hyomandibular cartilages (hyo) elongated, laterally compressed, articulating with hyomandibular facet on otic region of neurocranium, from where they project anterolaterally ( Fig. 6 ). Hyomandibula articulates with Meckel’s cartilage (Mc) by means of robust hyomandibular-Meckelian ligament. Embedded within ligament occur anterior (aac) and posterior angular cartilages (pac); anterior angular more robust than posterior. Meckel’s cartilage and palatoquadrate (pq) flattened; antimeres of both arches not fused symphysially, separated by short space containing strong horizontal ligaments. Posteriorly, between palatoquadrates and Meckel’s cartilages occurs a circular aperture formed by inferior surface of palatoquadrate and superior portion of Meckel’s cartilage. Palatoquadrate slightly arched, relatively straight on dorsal border and with pronounced curvature on ventral margin. Posterior triangular projections (ptp) present close to lateral edges of palatoquadrates. Palatoquadrates become progressively narrow in direction of midline. Meckel’s cartilages more arched than palatoquadrates, slender near symphysis, with evident rounded posterior margins, and with a pronounced concavity on inner corners that articulate with palatoquadrates.A marked curvature present on external aspect of Meckel’s cartilage for attachment of robust hyomandibular ligament. Ventrolateral processes (vlp) projecting from both extremities of Meckel’s cartilages.

Synarcual. The cervicothoracic or anterior synarcual articulates with neurocranium between occipital condyles by a median, anterior protuberance from anteroventral extremity of synarcual, the odontoid process (otp). The medial crest (mdc) corresponds to an anteroposterior dorsal crest present on synarcual ( Fig. 7 ). Spinal nerve foramina (snf) present along lower portion of synarcual, adjacent to lateral bulge of spinal nerve canal (snc). A lateral stay (ls) projects dorsally from lateral wall of synarcual. Suprascapulae firmly fused posterodorsally on synarcual through a socket and condyle articulation (asp) with scapular processes.

Pectoral girdle. Coracoid cartilage dorsoventrally flattened located ventral to synarcual ( Fig. 8 ). Several foramina for muscles, nerves and condyles for the pectoral pterygia are located on the lateral surface of pectoral girdle. The procondyle (pc), mesocondyle (msc) and metacondyle (mtc) are situated along the horizontal axis of the scapular cartilage. Anterodorsal fenestrae (adf) occur dorsal to the condyles, and anteroventral fenestrae (avf) occur ventrally. Posterodorsal (pdf) and posteroventral (pvf) fenestrae are also present. The anterior fenestrae have wider apertures in relation to the posterior ones. The scapular processes, comprising the dorsal tips of pectoral girdle, firmly articulate with lateral faces of synarcual.

Pelvic girdle. The pelvic girdle ( Fig. 9 ) consists of a puboischiadic bar (pib), a median prepelvic process (ppp), iliac processes (ip), lateral prepelvic processes (lpp), and isquial processes (isp). The puboischiadic bar is slightly arched, with lateral extremities widened where the three obturator formanina (of) are located. The prepelvic process consists of an anterior elongated projection. Robust and posterodorsally directed iliac processes are present on the lateral extremities of the puboischiadic bar. Triangular and well developed isquial processes are located on the inner corners of pelvic girdle posterior concavity. Short, robust and anterolaterally directed lateral prepelvic processes are present on each anterolateral corner of puboischiadic bar.

Claspers. Clasper skeleton ( Fig. 10 ) consists of the following cartilages: dorsal marginal (dm), ventral marginal (vm), dorsal terminal 2 (dt2), accessory terminal (at), ventral terminal (vt), axial cartilage (ax), two basal segments (b1 and b2) and a single beta cartilage (be). Dorsal terminal 2 long, relatively narrow and oval-shaped with a groove present along its proximal portion. Outer edges of dorsal marginal and dorsal terminal 2 forming the clasper groove externally. Inner edge of posterior portion of dorsal marginal forming dorsal pseudosiphon externally. Accessory terminal elongated and fusiform, underlying dorsal terminal 2, and forming ventral pseudosiphon externally from its outer edge. Ventral terminal broad, long and oval. Ventral marginal long and narrow, with pronounced anterior tip. Axial cartilage straight, depressed anterioly and distally cylindrical, tapering toward extremity. First basal segment (b1) connecting to basipterygium and second basal segment (b2) linked to proximal part of axial cartilage. Beta cartilage originating at first basal segment and distally articulated with dorsal marginal.

Geographical distribution. Potamotrygon falkneri occurs in the Paraná-Paraguay (Manso, Aricá-Mirim, Casca, Piquiri, Cuiabá, and upper Paraná Rivers) and La Plata ( lower Paraná and Colastiné Rivers, Santa Fé stream, and lago Setúbal) basins, and in the upper Amazon drainage in Bolívia (Madre de Díos, Guaporé, and Beni Rivers), Peru (Madre de Díos and Marañon Rivers), and Brazil ( rio Solimões ) ( Fig. 11 ).

Remarks. Specimens of Potamotrygon in the Museu Florentino Ameghino (MFA, Santa Fé, Argentina) were precariously preserved, having lost their original identification tags made of small, circular aluminum plates. The holotype of Potamotrygon menchacai (MFA 289, an adult male) and the paratype of Potamotrygon castexi (MFA 288, also an adult male) – the only remaining type-material of these nominal species still expected to be available – could not be found during a visit to the MFA. An attempt was made to identify type-material based on the measurements presented in their original descriptions, but their coloration was usually completely faded, and parts of the disc and tail were damaged or missing, all of which made locating type-material on the basis of secondary information very difficult. Rosa (1985) comments on the unfortunate condition of the paratype of P. castexi (MFA 288) in the early 1980’s, exemplified by the numerous damaged parts of disc, broken tail, and missing caudal sting and jaws. Although the holotype of P. menchacai was also examined by Rosa and seemed to be well preserved at that time, it also could not be found during our visit to the MFA.

The holotype of Potamotrygon castexi (MACN 5777), originally deposited in the Museo Argentino de Ciencias Naturales Bernardino Rivadavia (Buenos Aires) was previously reported to be lost ( Rosa, 1985), which was confirmed during our visit to that institution. According to Rosa (1985), the holotype dried in storage at MACN and could have been discarded. A paratype (ILAFIR 100), previously deposited in the Instituto Latino Americano de Fisiologia Reprodutiva ( Universidad del Salvador, San Miguel), and subsequently transferred to MACN, was also not found during our visit.

Although collection numbers of the two type-specimens of P. falkneri ( Fig. 2 ) were not given in the original description, we do not follow Castex (1964) in recognizing MFA 235 as the holotype of this species. According to the ICZN (1999, Chapter 16, Articles 73.1.1 and 73.1.3), the holotype of a new nominal species-group taxon can only be fixed in the original publication and by the original author using the expressions “ holotype or “the type” (or equivalent expression; holotype is the specimen fixed by original designation). This is not the case of specimen MFA 235 as it does not correspond with the description of the specimen figured as “type” in the original description (not matching in size). Specimen MFA 235 is probably part of the type series, as it is indicated in the collection list at MFA as “type” (and also according to Castex, 1964), but should therefore be treated as a paratype ( ICZN 1999, Chapter 16, Article 72.4.5). Note that this interpretation is in accordance with Rosa (1985), who previously identified specimen MFA 236 as the holotype (which is presently lost), on the basis that MFA 235 did not correspond with the specimen figured as “type” in the original description of Castex & Maciel (1963). According to Rosa (1985), the identification of the holotype was based on the comparison of the measurements given for the type with those of specimen MFA 236, and by matching details of the color pattern of MFA 236 with the photograph of the type in the original description. Specimen MFA 235 ( paratype), however, is the only remaining typespecimen of P. falkneri , and is in a poor state of conservation. Some parts of the disc are damaged, such as a large portion of the left side of the disc. The jaws were removed, and both dorsal and ventral coloration have become dark brown due to what appears to be putrefaction. The paratype could be confidently identified, however, due to its metal tag that was still attached to the dorsal surface of disc, although barely legible due to corrosion. Measurements of this specimen closely correspond with those given for the second specimen in the original description, and also agree with it in gender.

Figures

Fig. 1. Dorsal and ventral views of Potamotrygon falkneri specimens. A-B. NUP 2923, male, 380 mm DW (rio Cuiabazinho, State of Mato Grosso, Brazil); C-D. NUP 2917, female, 325 mm DW (same data as A and B).

Fig. 2. Paratype of Potamotrygon falkneri (MFA 235, female, 286 mm DL) in dorsal (A) and ventral (B) views (río Paraná, Província de Santa Fé, Argentina); (C) dorsal view of paratype of P. falkneri (MFA 235, as in A-B); (D) holotype in dorsal view of P. falkneri (MFA 236, female, 491 mm DL). C and D from M. Castex’s archive in MFA; photograph not dated but probably from the early 1960‘s.

Fig. 3. Dermal denticles of Potamotrygon falkneri in dorsal view, from mid region of back; A. Denticle arrangement; B. Individual dermal denticle amplified; cd, crown dichotomy; cp, crown plate; cr, crown ridge.

Fig. 4. Ventral lateral line canal system of Potamotrygon falkneri. (A) MZUSP 106258, female, 292 mm DW; (B) MZUSP 106262, male, 273 mm DW; ast, anterior subpleural tubules; hjc, hyomandibular jugular component; hsc, hyomandibular subpleural component; hyoc, hyomandibular canal; ioc, infraorbital canal; iol, infraorbital loop; jug, jugular canal; man, mandibular canal; nas, nasal canal; ocs, orbitonasal component of supraorbital canal; pnl, prenasal loop; pst, posterior subpleural tubule; sci, suborbital component of infraorbital canal; soc, supraorbital canal; sol, suborbital loop; spl, subpleural loop.

Fig. 5. Dorsal (A), ventral (B), lateral (C) and posterior (D) views of neurocranium of Potamotrygon falkneri (MZUSP 106265, male, 231 mm DW); acvf, anterior cerebral vein foramen; afpc, anterior foramen for preorbital canal; anc, antorbital cartilage condyle; as, articular surface; elf, endolymphatic foramen; es, eye-stalk; esaf, efferent spiracular artery foramen; fpf, frontoparietal fontanelle; fm, foramen magnum; hmdf, hyomandibular facet; icaf, internal carotid artery foramen; ivf, interorbital vein foramen; lc, lateral commisure; nc, nasal capsule; obf, orbital fissure; oc, occipital condyle; pcf, precerebral fontanelle; pfpc, posterior foramen for preorbital canal; plf, perilymphatic foramen; pop, postorbital process; pq, palatoquadrate; prp, preorbital process; soc, supraorbital crest; sp, supraorbital process; sup, superficial ophthalmic nerve foramina; II, optic nerve foramen; III, oculomotor nerve foramen; VII, hyomandibular branch of facial nerve foramen; IX, glossopharyngeal nerve foramen; X, vagus nerve foramen.

Fig. 6. Dorsal view of hyomandibular arch of Potamotrygon falkneri (MZUSP 106265, male, 231 mm DW); aac, anterior angular cartilage; hyo, hyomandibula; Mc, Meckel’s cartilage; pac, posterior angular cartilage; pq, palatoquadrate; ptp, posterior triangular projection; vlp, ventrolateral process.

Fig. 7. Dorsal (A) and lateral (B) views of synarcual cartilage of Potamotrygon falkneri (MZUSP 106265, male, 231 mm DW); asp, articular surface for scapular process; ls, lateral stay; mdc, medial crest; otp, odontoid process; snc, spinal nerve canal; snf, spinal nerve foramen.

Fig. 8. Lateral view of pectoral girdle of Potamotrygon falkneri (MZUSP 106265, male, 231 mm DW); adf, anterodorsal fenestra; avf, anteroventral fenestra; msc, mesocondyle; mtc, metacondyle; pc, procondyle; pdf, posterodorsal fenestra; pvf, posteroventral fenestra.

Fig. 9. Dorsal view of pelvic girdle of Potamotrygon falkneri (MZUSP 106265, male, 231 mm DW). ip, iliac process; isp, ischial process; lpp, lateral prepelvic process; of, obturator foramen; ppp, prepelvic process; pib, puboischiadic bar.

Fig. 10. Dorsal (A) and ventral (B) views of clasper of Potamotrygon falkneri (MZUSP 108683, male, 365 mm DW); at, accessory terminal; ax, axial cartilage; b1, first basal segment; b2, second basal segment; be, beta cartilage; dm, dorsal marginal; dt2, dorsal terminal 2; pvr, pelvic fin radial; vm, ventral marginal; vt, ventral terminal.

Fig. 11. Map showing geographic distribution of Potamotrygon falkneri and Potamotrygon sp. Circles indicate distribution of P. falkneri, square indicates locality of specimens of Potamotrygon sp., and star indicates type locality of P. falkneri.