Potamotrygon scobina Garman 1913

• Main Authors: Fontenelle, João Pedro, De Carvalho, Marcelo R.
• Format: Text
• Language: unknown
• Published: Zenodo 2017
• Subjects: Biodiversity; Taxonomy; Animalia; Chordata; Elasmobranchii; Myliobatiformes; Potamotrygonidae; Potamotrygon; Potamotrygon scobina; Clayton; Crown Head; Ferreira; Keyhole; Maciel; Northwest Atlantic
• Online Access: https://dx.doi.org/10.5281/zenodo.5618456; https://zenodo.org/record/5618456

Potamotrygon scobina Garman, 1913 (Figs. 2–14, 32, 43; Tables 1 –2) Potamotrygon scobina Garman 1913, p. 418 (original description, rio Tocantins at Cametá, Pará, Brazil, not illustrated); Castex 1964, p. 27 (brief characterization); Castex & Maciel 1965, p. 15 (citation); Rosa 1985, pp. 324–335, figs. 22D, 79–81 (taxonomic review, redescription); Compagno & Cook 1995, pp. 72, 74, 80 (listed); Compagno 1999, pp. 495 (listed); Ross & Schäfer 2000, pp. 46, 48, 120, fig. S66080 -3 (listed); Marques 2000, p. 46 (molecular study of parasites); Carvalho et al . 2003, p. 25 (listed); Almeida 2003, pp. 1–118, appen. 4–6 (systematic and biological aspects); Bragança et al . 2004, pp. 49–59 (feeding); Charvet-Almeida et al . 2005, pp. 165–171 (reproduction); Compagno 2005, p. 541 (listed); Deynat 2006, p. 491 (citation); Magalhães et al . 2006, pp. 575–583 (venom biochemistry); Rapp Py-Daniel et al . 2007, pp. 95, 107, 122, fig. 5 (listed); Toffoli et al . 2008, p. 324 (molecular study of family); Montag et al . 2009, pp. 247, 252 (listed); Almeida et al . 2009, pp. 1–11 (distribution); Duncan et al . 2010, pp. 21, 22, 25 (gill physiology); Carvalho & Shibuya 2013, pp. 72, fig. on p. 76 (identification, rio Madeira); Fontenelle 2013, pp. 1–226, figs. 1–14, 51–55 (taxonomic review); Rosa et al . 2014 pp. 256–260 (general biology); Fontenelle et al . 2014, pp. 249, 252, 264, 266, 267 (comparison with P. limai , described as new); Fontenelle & Carvalho 2016, pp. 253, 256, 257, fig. 5 (morphology of brain). Paratrygon scobina : Fowler 1948, p. 10 (listed). [non] Potamotrygon scobina : Ferreira et al . 2011, p. 121 (listed); Ross & Schäfer 2000, pp. 120, 121, figs. S66091 -4, S66092 - 2 (listed); Lasso et al . 2014 pp. 83, 110, fig. 79 (photos). Holotype . MCZ 602 s, juvenile male, coll. Thayer Expedition (Figs. 2–5). Type locality . Rio Tocantins at Cametá, Pará state, Brazil. Diagnosis . Potamotrygon scobina is distinguished from congeners by a combination of characters: disc dark brown to dark gray with relatively small beige to yellow ocelli with thin dark brownish contours; ocelli usually smaller on central disc, varying in number and size, sometimes forming rosette-like patterns or grouped around a central larger ocellus; ventral disc whitish, with darker blotches over posterolateral margins; tail dark, with nonocellated, irregular, light colored spots; labial folds absent; teeth small, with a single low cusp; dermal denticles small and relatively few in number, concentrated mostly on central disc; disc margins usually lacking denticles; rostral denticles simple, composed of a single central crown; head denticles with low, star shaped crowns; caudal denticles with same pattern as head, but smaller; one or two irregular rows of thorns on dorsal tail midline, always converging to a single row posteriorly; thorns relatively large and curved; tail long and slender, with a narrow base; cartilaginous rod notably very long and thin; a third, smaller, lateral angular cartilage present. Potamotrygon scobina is distinguished from congeners by its color pattern (further detailed below) and in having a third, smaller, lateral angular cartilage, except P. limai , P. adamastor sp. nov. , P. garmani sp. nov. , and P. amazona sp. nov. From P. limai , P. scobina is further distinguished by lacking its polygonal color pattern on disc, and by having a thinner tail and dermal denticles with lower crowns and fewer dichotomies. From P. amazona sp. nov. and P. adamastor sp. nov. , by having a less muscular disc in adults, comparatively smaller and fewer dermal denticles, larger and better defined ocelli on disc, and a more slender and longer tail (mean tail width 13.4% DW vs . 19.0% DW in P. adamastor sp. nov. and 16.7% DW in P. amazona sp. nov. mean tail length 121.5% DW vs . 78.1% DW in P. adamastor sp. nov. and 89.3% DW in P. amazona sp. nov. ). From P. garmani sp. nov. , P. scobina is differentiated by presenting a darker disc background, smaller ocellated spots, a longer and more slender tail (mean length 121.5% DW vs . 100.6% DW in P. garmani sp. nov. mean width 13.4% DW vs . 14.1% DW in P. garmani sp. nov. ), more tooth rows in both jaws (44/48–50 vs . 32–40/ 33–40 in P. garmani sp. nov. ), and in having comparatively smaller thorns in dorsal mid tail series. Description . Disc oval, slightly longer than wide (DL 98.8–112.4% DW) (Figs. 2, 6). Rostral portion of disc broadly oval, presenting a small round protuberance on anterior snout (Figs. 3 a, 7a). Disc dorsoventrally slender and comparatively thin at margins. Eyes small and oval (mean 3.0% DW), around two times smaller than spiracles; spiracles rhomboidal, obliquely set just posterior to eyes (Figs. 3 a, 7a). Head flat, low, not abruptly or significantly raised above disc, head length about 1/3 of disc length, with interorbital distance 12.9–17.5% DW, and interspiracular distance 15.9–21.5% DW. Nasal curtain extending to mouth opening. Mouth small and lightly undulated or convex, with a central notch; mouth width 7.1–12.5% DW, and internasal distance 7.3–9.2% DW (Figs. 3 b, 7b). No labial folds or ridges present. Five buccal papillae present on mouth floor, two posterior and three anterior; three papillae in a single row on mouth roof. Branchial basket wider than long, with distance between first branchial slits 23.1–29.0% DW, and distance between fifth branchial slits 15.9–21.2% DW. Teeth small, simple and rounded, wider than long, set in quincunx on narrow and arched upper tooth plate, and wide and trapezoidal lower tooth plate (Figs. 4 a–d, 8). Tooth row count 40 in upper jaw and 48–50 in lower jaw. Adult males presenting a single, central pointed cusp on midrow teeth in both jaws. Lateral teeth in adult males, juvenile males, and females simple, with a single rounded cusp. All teeth with a single cutting surface. Lower jaws considerably wider than upper jaws, always with more tooth rows. Pelvic fins broad, subtriangular, their length ranging from 23.7–60.3% DW (mean 52.8% DW), with rounded apices and undulated posterior margins (Figs. 3 d, 7d). Pelvic fin posterior margins project slightly beyond posterior disc. Anterior pelvic margin length varying from 20.5–27.8% DW. Claspers robust, long and dorsoventrally compressed (Fig. 7 d). Clasper base more robust and wider than clasper tip. Clasper external length 3.9–14.2% DW, and internal length 7.9–21.5% DW (considering juveniles and adults). Clasper groove curved medially, with a semicircular apopyle, and an oval and large hypopyle. Dorsal pseudosiphon oval, obliquely positioned. Ventral pseudosiphon well developed, elliptical and medial. Tail slender, long and well developed (Figs. 6, 7 c). Tail width ranging from 10.1–20.2% DW (mean 13.4% DW), and length ranging from 76.3–145.2% DW (mean 121.6% DW). Tail narrows only slightly from base to caudal sting origin, then tapers posteriorly more intensely toward extremity. Long and slender cartilaginous rod present internally in tail more or less as of caudal sting, its length generally 1/2–2/3 of total tail length. A single irregular dorsal row of tail thorns present; thorns with a wide and round basal plate and posteriorly curved, only moderately developed crown; sometimes two irregular rows present on tail base. Tail also with small and scattered denticles. Small, single lateral row of spine on tail, originating at caudal sting origin. Caudal sting length 13.8– 25.8% DW. Coloration . Dorsal disc dark brown to dark gray (Figs. 3 c, 9), with small white to yellow irregular spots, varying in number. Beige to yellowish ocelli present, their outer halo thin, darker, and poorly defined; ocelli same size or smaller than eyes, but usually larger between disc margins and center; ocelli spread over all of disc. Smaller irregular whitish spots sometimes present, set around a central, larger ocellated spot. Four main color patterns observed, but intermediate specimens also exist: (i) disc dark brown, with relatively large ocelli varying in quantity, and without accessory smaller spots; (ii) disc dark brown, with large ocellated spots, and with accessory small and irregular whitish spots mainly on posterior dorsal portion of disc; (iii) disc dark brown, with few, small ocelli, and sometimes very small accessory spots; (iv) disc dark background with numerous irregular whitish spots, sometimes organized around ocelli; ocelli sometimes discernible only on disc margins, but present on tail base and dorsal pelvic fins. Ventral disc white to creamy-white, sometimes with central darker spot. Subadults and adults with ventral posterolateral dark gray blotches on disc, extending anteriorly to level of pectoral girdle. Ventral darker pigmentation age related; younger specimens generally lighter. Dorsal pelvic fins with same pattern as disc margins, with a dark background and ocellated spots. Posterior pelvic margin with lighter color. Ventrally, pelvic fins light with a posterior dark margin, varying with specimen size and age. Claspers dorsally with same background pattern as pelvic fins, but with irregular clear spots, without ocelli. Ventrally, claspers dark. Dorsal tail dark, similar to dorsal disc color, covered by small irregular, whitish spots. Lateral tail with small, spaced groupings of very small whitish irregular spots. Ventrally, tail whitish, covered by dark blotches, continuous with those of disc. Dark blotches progressively smaller from anterior to posterior tail. Adults may present a more uniform dark ventral tail. Newborn specimens may present proportionally larger marginal ocelli combined with a central roughly hexagonal pattern of smaller spots on disc (newborn frequently misidentified as P. motoro or P. orbignyi ). Dermal denticles . Dermal denticles small and comparatively few, present on central snout, head, posterocentral disc, and dorsal and lateral tail (Figs. 4 e–h, 10, 11). Disc margins smooth, denticles either absent or very small and sparse. Simple denticles present between eyes in a semicircular pattern, with a single, low pointed crown. Denticles usually uniform in size, but larger denticles reach up to twice size of smaller denticles. Denticle basal plate ( Bp ) rounded and low. Denticles on head and central posterior disc regions star shaped, with a posteriorly set, well-developed coronal plate ( Cp ). Anterior end of coronal plate wider and obliquely set. Two anterior coronal ridges ( Cr ) present with two different levels, marked by a central rounded notch, and converging to anterior end of coronal plate. Two posterior coronal ridges present, straight and opposite, laterally set to posterior end of coronal plate. Irregular coronal dichotomies ( Cd ) sometimes present on coronal ridges. Denticles of caudal region with well-developed coronal plates, curved posteriorly, with two anterior and two lateral posterior coronal ridges. Basal plate fairly prominent on disc denticles. Caudal denticles more prominent, simpler and with more slender crowns than denticles on central disc. One irregular row of enlarged thorns over most of tail, with one to two irregular thorn rows over tail base. Enlarged thorns moderately robust, presenting a single posteriorly set crown and semi-oval basal plate. Lateral caudal spine rows sometimes present, posterior to origin of caudal sting, and composed of minute denticles with single crowns. Ventral lateral-line canals . (Fig. 12). Hyomandibular canal ( HYC ) projecting anteriorly from the nostril and obliquely towards disc margins, curving posteriorly following anterolateral disc margin. Anterior subpleural tubules ( AST ) short and straight. Subpleural component of the hyomandibular canal ( SPC ) slightly undulated, projecting posteromedially. Hyomandibular canal abruptly curves inward by anterior margin of pelvic fin, forming the subpleural loop ( SPL) . Posterior subpleural tubules ( PST ) absent. Jugular component ( JCH ) projects anteriorly and obliquely, bordering external margin of branchial basket. Jugular canal ( JUG) curved externally, extending anteriorly to the small loop formed by the supraorbital canal ( SOC) . From the posterior jugular loop ( PJL ), the posterior portion of the infraorbital canal ( IOC ) projects posteroexternally forming the external margin of the short posterior jugular loop ( PJL ). Infraorbital canal extends anteriorly, parallel to the anterior expansion of the hyomandibular canal. At its most anterior segment, the infraorbital canal curves medially to delimit the anteriorly positioned suborbital loop ( SOL ). Nasal canal ( NAS ) projects anteriorly, curving medially as it reaches nostril. The orbitonasal component ( CON ) of the supraorbital canal ( SOC ) extends anteromedially from the confluence between the jugular and nasal canals, forming the lateral margin of the anterior jugular loop ( AJL ). The orbitonasal component extends toward the ventral snout area, presenting undulations varying in size, and forms the lateral margin of the acutely shaped prenasal loop ( PNL ). Skeletal morphology . Neurocranium . Nasal capsules ventrolaterally expanded ( NC ) (Figs. 5, 13), their anterior margin oval and convex. Precerebral fontanelle ( PCF ) wide and subcircular, with straight anterior margins, posteriorly delimited by a subtriangular epiphysial bar ( EBP ). Frontoparietal fontanelle ( FPF ) coneshaped, progressively narrowing posteriorly, presenting a slight median constriction, with a round posterior margin at posterior level of postorbital processes. Together, both fontanellae keyhole-shaped. Supraorbital processes ( SOP ) small, subtriangular, laterally projected. Postorbital process ( POP ) prominent, long and wide, diagonally projected anteriorly, extending to level of posterior angular cartilage. Prespiracular cartilage ( psc ) curved, forming a concave anterior wall to the spiracle. Jaws and hyomandibular arch . Hyomandibular cartilage ( HYO ) elongated and anterolaterally projecting from neurocranium, bearing a slight lateral constriction close to posterior extremity; anterior margin of hyomandibulae curved (Figs. 5 b, d, 13b, d, 42). Three angular cartilages present. Anterior angular cartilage ( AAC ) concave, about 1/4 length of hyomandibulae. Posterior angular cartilage ( PAC ) oval, around same size of anterior angular cartilage, but more slender than anterior angular cartilage. Lateral angular cartilage ( LAC ) subcircular and small, set between posterior angular cartilage and hyomandibulae, around 1/3 length of posterior angular cartilage. Meckel's cartilage ( MC ) robust, its internal margin with subrectangular corners, and rounded external margins. Well defined, central concavity present on anterior margin of Meckel's cartilage. Posterior margin bearing a prominent, anterior ventrolateral process ( VLP ), not contacting angular cartilages, and a robust anterolateral process ( LAP ). Palatoquadrate ( PQ ) smaller and more slender than Meckel's cartilage, with a posterior concavity, laterally limited by a small triangular projection. Posterior triangular projection ( PTP ) well developed. Small ligament present between palatoquadrate antimeres. Synarcual cartilage . Anterior synarcual articulates with neurocranium through a rounded, central odontoid process (Fig. 5 b). Medial crest extending over almost entire synarcual length, but not reaching its anterior extremity. Articular surfaces for scapular processes laterally projected, separated by concavity on each side. Anterior articular surface slightly rectangular and more prominent then rounded and lateroposteriorly projected posterior articular surface. Pectoral girdle . Pectoral girdle articulates with synarcual through robust scapular processes (Figs. 5 a, 13c). Anterior process slender and straight, projected diagonally; posterior process more robust, with a small rounded extremity delimiting an adjacent concavity. Scapular process presents a biconcave medial bar, with considerably expanded lateral portions. Procondyle ( PRC ) anteriorly positioned, rounded. Mesocondyle ( MSC ) rounded, anterolaterally positioned; metacondyle ( MTC ) rounded, but less so, posteriorly positioned. Robust and elongated propterygium ( PRO ) articulated anteriorly to procondyle and scapular girdle. Mesopterygium ( MES ) small, its anterior margin more developed, articulating to shoulder girdle near mesocondyle. Metapterigium ( MET ) posteriorly set and elongated, articulates at level of metacondyle ( MTC ), and curved, projecting posteriorly. Pelvic girdle . Prepelvic process ( PPP ) elongated, anteriorly projected, bordered by anterior concavities of pubosquiadic bar ( PIB ); puboischiadic bar with expanded extremities (Figs. 5 c, 13e, f). Evident subtriangular lateral prepelvic processes ( LPP ) present. Iliac processes ( IP ) laterally and posteriorly set and robust. A slender and subtriangular isquial process ( ISP ) set more medially, projecting posteriorly. Between both isquial processes, four well developed obturator foramina ( OF ) present on each side. Clasper skeleton. Basal segment 1 ( B1 ) with a wider anterior margin (Figs. 13 f, 14); both margins oval. Basal segment 2 ( B2 ) cylindrical, with a central concavity on its external wall. Both basal segments about equal in length, but segment 2 more slender. Axial cartilage ( AX ) elongated and cylindrical, robust, curved externally, S-shaped posteriorly. Ventral marginal cartilage ( VM ) diamond-shaped, projecting laterally and ventrally. Beta cartilage ( BE ) slender and cylindrical, about 1/2 of total clasper length, and externally curved, articulating with basal segment 1. Dorsal marginal cartilage ( DM ) well developed and oval, about 1/ 4 in total clasper length, curved internally. Dorsal terminal 2 ( DT2 ) oval, slightly slender and curved, presenting a small concavity on its anterior margin. Accessory terminal cartilage ( AT ) straight, more robust than dorsal terminal 2, dorsal marginal and ventral marginal cartilages, with a curved anterior margin. Ventral terminal cartilage ( VT ) well developed, about 1/3 of clasper length, with a dilated posterior portion but rest of structure dorsally curved, almost completely covering accessory terminal cartilage. Geographic distribution . Potamotrygon scobina is widely distributed in the Amazon basin (Fig. 43). Examined specimens are from rio Tocantins (including specimens from very close to type locality) and rio Madeira systems, as well as from rios Amazonas and Solimões. There are also records from río Orinoco in Colombia and Venezuela (Rosa et al. 2014; also possibly Ross & Schäfer 2000), and scobina -like specimens occur as far as rio Nanay, in Peru (M. Kolmann, pers. comm); many of : Published as part of João Pedro Fontenelle & Marcelo R. 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