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Taxon profile

species

Largespot River Stingray
Potamotrygon falkneri Castex, 1963

kingdom Animalia - animals »  phylum Chordata - chordates »  class Chondrichthyes - cartilaginous fishes »  order Batoidei - rays and skates »  family Potamotrygonidae - river stingrays »  genus Potamotrygon

Scientific synonyms

Potamotrygon castexi Castello & Yagolkovski, 1969
Potamotrygon menchacai Martínez Achenbach, 1967

Other names

= Vermiculate River Stingray

Images

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Description

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 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.

External morphology. Disc oval, 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. 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. 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. 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). 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.

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).

Size

Total length may reach almost 90 cm. Disc length over 55 cm.

Sources

SILVA, João Paulo C. B. da and CARVALHO, Marcelo R. de. A taxonomic and morphological redescription of Potamotrygon falkneri Castex & Maciel, 1963 (Chondrichthyes: Myliobatiformes: Potamotrygonidae). Neotrop. ichthyol. [online]. 2011, vol.9, n.1, pp. 209-232. ISSN 1679-6225.
Author: Petr Čech

Links and literature

CZ AQUATAB. World Wide Web electronic publication [species/28390]

Plíštil J. (Ed.) (2009): AQUATAB. World Wide Web electronic publication [http://aquatab.net] [as Potamotrygon castexi Castello & Yagolkowski, 1969]
Data retrieved on: 17 January 2010
CZ AQUATAB. World Wide Web electronic publication [species/28392]

Plíštil J. (Ed.) (2009): AQUATAB. World Wide Web electronic publication [http://aquatab.net] [as Potamotrygon falkneri Castex & Maciel, 1963]
Data retrieved on: 17 January 2010
CH DE EN FR IT NL PR SP FishBase [53762]

Froese R., Pauly D. (eds.): FishBase [http://www.fishbase.org]
EN IUCN Red List of Threatened Species 2013.2 [161572]

IUCN Red List of Threatened Species [http://www.iucnredlist.org/] [as Potamotrygon castexi Castello & Yagolkowski, 1969]
Data retrieved on: 27 January 2014
EN IUCN Red List of Threatened Species 2013.2 [161353]

IUCN Red List of Threatened Species [http://www.iucnredlist.org/] [as Potamotrygon falkneri Castex & Maciel 1963]
Data retrieved on: 28 January 2014
CZ Hanel L., Novák J. (2001): České názvy živočichů V. Ryby a rybovití obratlovci (Pisces), 1. Sliznatky (Myxini), mihule (Cephalaspidomorphi), paryby (Chondrichthyes), Národní muzeum, (zoologické odd.), Praha, 53 pp. [as Potamotrygon castexi Castello & Yagolkovski, 1969]
Data retrieved on: 2 June 2013
CZ Hanel L., Novák J. (2001): České názvy živočichů V. Ryby a rybovití obratlovci (Pisces), 1. Sliznatky (Myxini), mihule (Cephalaspidomorphi), paryby (Chondrichthyes), Národní muzeum, (zoologické odd.), Praha, 53 pp. [as Potamotrygon falkneri Castex, 1963]
Data retrieved on: 2 June 2013
EN Veríssimo, S.; C. S. Pavanelli; H. A. Britski; M. M. M. Moreira. (2005): Fish, Manso Reservior region of influence, Rio Paraguai basin, Mato Grosso State, Brazil. [http://www.checklist.org.br/getpdf?SL002...], Check List 1(1):1-9PDF [as Potamotrygon falkneri Castex & Maciel, 1963]

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