Potamotrygon garmani, João Pedro Fontenelle & Marcelo R. De Carvalho, 2017

João Pedro Fontenelle & Marcelo R. De Carvalho, 2017, Systematic revision of the Potamotrygon scobina Garman, 1913 species-complex (Chondrichthyes: Myliobatiformes: Potamotrygonidae), with the description of three new freshwater stingray species from Brazil and comments on their distribution and biogeography, Zootaxa 4310 (1), pp. 1-63 : 43-54

Potamotrygon garmani , sp. nov.

( Figs. 33–43 ; Tables 7–8)

Holotype. UNT 2174 (adult? male, 341 mm DW), rio Paranã, municipal district of Paranã, affluent of rio Tocantins, rio Tocantins basin, state of Tocantins, Brazil, 12°30’S, 48°12’ W, coll. staff of NEAMB. ( Fig. 33 )

Paratypes. (3 specimens). UNT 2173 (subadult male, 405 mm DW), rio Santa Tereza , municipal district of Peixe, rio Tocantins, Tocantins basin, state of Tocantins, Brazil, 11°48’7”S, 48°38’21”W, coll. staff of NEAMB ; UNT 2175 (subadult male, 350 mm DW), rio Tocantins, municipal district of Peixe , near the confluence with rio Santa Tereza, Tocantins basin, state of Tocantins, Brazil, 11°47’27”S, 48°37’2”W, coll. staff of NEAMB ; UNT 2178 (adult female, 428 mm DW), same data as holotype ( Fig. 34 ).

Diagnosis. Potamotrygon garmani sp. nov. is distinguished from congeners, except P. limai , P. scobina , P. amazona and P. adamastor , by a combination of characters: disc dorsoventrally slender, with a light to dark brown dorsal color, and ocelli with beige, light yellow and whitish centers and a dark brown contour; ocelli mostly similar in size throughout disc but smaller ocelli sometimes present; small dermal denticles on central disc; disc margins usually without denticles; rostral denticles simple, with a single central cusp and a star-shaped basal plate; head denticles present star-shaped crowns, with one anterior and one posterior dichotomy lateral to the central cusp; caudal denticles present a central coronal plate and one anterior dichotomy; a third angular cartilage present; one or two irregular rows of thorns on dorsal tail midline, converging to a single row posteriorly; tail long and thin, with its base somewhat narrow; cartilaginous rod long, about same length as anterior portion of tail. Potamotrygon garmani sp. nov. is separated from P. limai by not having a reticulate or polygonal pattern on disc, by having a longer tail (100.6% DW vs. 86.3% in P. limai ), and by having dermal denticles with fewer dichotomies and ridges. From P. amazona and P. adamastor by having a more slender disc, with less-developed disc musculature, smaller and fewer dermal denticles, greater and more defined ocellated spots on disc, and a more slender and longer tail (mean tail width 14.1% DW vs. 19.0% DW in P. adamastor and 16.7% DW in P. amazona ; mean tail length 100.6% DW vs. 78.1% DW in P. adamastor and 89.3% DW in P. amazona ). Finally, P. garmani sp. nov. is distinguished from P. scobina by presenting a brown disc, by having larger ocellated spots, tail shorter and wider (mean tail length 100.6% DW vs. 121.5% DW in P. scobina ; mean tail width 14.1% DW vs. 13.4% DW in P. scobina ), fewer teeth on both jaws (32–40/33–40 vs. 44/ 48–50 in P. scobina ), and more thorns in dorsal mid-tail rows.

Description. Disc subcircular, slightly longer than wide (its length 102.6–109.3% DW) ( Figs. 33 , 34 ). Disc anterior margin convex, presenting a small round protuberance on snout ( Fig. 35 a). Disc dorsoventrally compressed and slender, with comparatively thin margins. Eyes small and oval (mean 3.5% DW), around two times smaller than spiracles; spiracles trapezoidal, obliquely set posterior to eyes ( Fig. 35 a). Small and faintly elevated head, about 1/3 of disc length, with interorbital distance 13.8–18.6% DW, and interspiracular distance 15.5–19.0% DW ( Fig. 35 a). Nasal curtain partially covering mouth, except at its margins. Mouth small and slightly undulated or convex, with a central notch (mouth width 8.6–10.2% DW, internasal distance 7.7–9.3% DW). Labial ridges absent ( Fig. 35 c). Five buccal papillae present, two posterior alternating with three anterior. Branchial basket wider than long, with space between first branchial slits 23.2–24.9% DW, and distance between fifth branchial slits 16.3–18.1% DW.

Teeth small, simple and rounded, wider than long, set in quincunx, in a narrow arched upper tooth plate and a wide and trapezoidal lower tooth plate ( Fig. 36 ). Tooth rows varying from 32–40 in upper jaw and 33–40 in lower jaw. Adult males present a single central pointed cusp on central teeth of both jaws. Lateral teeth in adult males, teeth in juvenile males, and teeth in females simple, presenting a single rounded cusp. All teeth present a single cutting surface.

Measurements N Holotype Range Paratype Range Mean SD Pelvic fins subtriangular, their length 48.0–61.1% DW (mean 55.4% DW), presenting round corners and an undulated posterior margin. Pelvic fin posterior margins slightly exposed posterior to disc ( Fig. 35 d). Length of anterior margins of pelvic fins 19.6–25.7% DW. Claspers robust and dorsoventrally compressed ( Figs. 35 b, d, e). Clasper base much more robust than tip; clasper external length 9.6–11.7% DW, and internal length 17.0–17.6% DW. Clasper groove long, extending posteriorly in a straight manner, with a semicircular apopyle at level of posterior margin of pelvic fins, and an oval and large hypopyle, subterminal, positioned more externally. Dorsal pseudosiphon oval, set obliquely; ventral pseudosiphon slightly greater.

Tail long and well developed, its width 11.9–16.4% DW (mean 14.1% DW), and length 71.0–115.2% DW (mean 100.6% DW) ( Figs. 33 , 34 ). Tail tapers posteriorly. Cartilaginous rod about 2/5 of total tail length, long and thin. Small and numerous denticles present, especially at origin of mid tail thorn rows. Tail also with lateral denticles in lateral spine rows as of sting origin. Caudal sting length 21.5–30.5% DW.

Coloration. ( Fig. 37 ). Dorsal disc light to dark brown with numerous small, white to yellow irregular spots, on disc; beige to yellowish ocelli also present, circled by dark contours; spots regular in size and well highlighted, never greater than eye-size. Ocelli spread all over disc, usually without any defined pattern of spots around them, but small irregular whitish spots sometimes set around a “central” ocellus, more common on disc margins. Ocelli smaller at disc margins, progressively larger toward disc center. Ocelli also on tail base and dorsal pelvic fins. Spots vary in size and number on dorsal disc and between different specimens. Ventral disc white to beige, lacking enlarged central black spot. Subadults and adults with dark blotches on posterolateral disc margins, extending anteriorly to level of mouth. Larger specimens darker. Pelvic fin dorsal surface with same color of disc margins; posterior margin lighter. Ventrally, pelvic fins whitish with a posterior dark margin, darker in larger specimens. Dorsal claspers brownish, with irregular non-ocelllated spots. Claspers dark ventrally. Tail dorsally brownish, similar to disc, with small irregular light colored spots, smaller than ocelli. Laterally, tail with small groupings of small light colored irregular spots, without ocelli. Ventrally, tail covered by dark blotches, continuous with those of disc. Dark blotches progressively larger from posterior to anterior tail. Adult specimens may present a completely dark ventral tail.

Dermal denticles. ( Fig. 38 ). Disc totally covered with dermal denticles, but more numerous in three specific regions. Disc margins with smaller and fewer denticles. Rostral region with simple denticles, with a single pointed crown without coronal ridges (Cr). Larger disc denticles with a pair of oblique, posterior small protuberances ( Fig. 38 b). Basal plate (Bp) low and barely apparent, with asymmetrical, robust basal ridges (Br), between 5 and 10 in number, coverging toward central cusp. Denticles of head and mid region of disc with star-shaped pattern, presenting a posteriorly oriented coronal plate (Cp), with two lateral posterior ridges that may present a terminal dichotomy, and two anteriorly converging robust and long coronal ridges (Cr), sometimes with an irregular surface; terminal dichotomies may be present. Lateral ridges smaller than anterior ones. Caudal region with a central well-developed coronal plate, curved posteriorly, with two well-developed anterior coronal ridges. These ridges may present a medial protuberance, creating a small discontinuation. Basal plate well developed and low, with many converging slender basal ridges. Two or three irregular thorn rows over tail base, with a single irregular thorn row over more distal tail anterior to caudal stings. Denticles present a robust, posteriorly oriented central cusp. Basal plate semicircular and varying in size and shape. Lateral spine rows sometimes present, composed of small denticles, originating at origin of caudal stings and extending posteriorly to tail tip.

Ventral lateral-line canals. ( Fig. 39 ). Hyomandibular canal (HYC) slightly undulated, projecting toward anterior disc from nostrils, deflecting toward outer disc margins; few short and straight subpleural tubules present (AST). Hyomandibular canal extends posteriorly as the subpleural component of the hyomandibular canal (SPC). Subpleural loop (SPL) relatively acute posteriorly, extending to level of pelvic fin origins. Posterior subpleural tubules not observed. Jugular component (JCH) projects anteriorly, slightly undulated, towards branchial basket. Angular component of hyomandibular canal (ACH) external to gill slits, not undulated, deflecting medially to form the jugular canal (JUG) anterior to first branchial slit, and forming the posterior jugular loop (PJL). From posterior jugular loop, infraorbital canal (IOC) extends externaly to form infraorbital loop (IOL). Infraorbital canal extends anteriorly, slightly undulated, and deflects medially parallel to hyomandibular canal. Suborbital loop (SOL) extends to posterior disc with few short undulations towards snout. Supraorbital canal (SOC) highly undulated, extending obliquely and anteroposteriorly lateral to mouth and nostrils. Orbitonasal component of supraorbital (CON) curves towards nostrils forming prenasal loop (PNL). Nasal canal (NAS) short and straight, directed toward mouth. Prenasal component of nasal canal (PNC) extends towards anterior snout from nostril.

Skeletal morphology. Neurocranium. Nasal capsules (NC) ventrolaterally expanded ( Fig. 40 ). Anterior margin of nasal capsules oval and convex, with an internal ventromedial sept dividing both capsules. Precerebral fontanelle (PCF) expanded and subcircular, with a straight anterior margin, posteriorly delimited by a subtriangular epiphysial bar (EBP). Frontoparietal fontanelle (FPF) triangular, progressively narrowing, with a round posterior margin at level of anterior margin of postorbital processes. Together, both fontanellae keyholeshaped. Postorbital processes (POP) prominent, long and narrow, diagonally projecting anterolaterally to posterior angular cartilage. Prespiracular cartilage (PSC) posteriorly curved.

Jaws and hyomandibular arch. ( Figs. 40 a, c). Hyomandibulae (HYO) elongated, anterolaterally projected, presenting a curved anterior margin. Three angular cartilages present. Anterior angular cartilage (AAC) slightly concave, around 1/5–1/4 length of hyomandibula. Posterior angular cartilage (PAC) more straight, slightly smaller and more slender than anterior angular cartilage. Lateral angular cartilage (LAC) subcircular, positioned between posterior angular cartilage and hyomandibula, and about 1/4–1/3 length of posterior angular cartilage. Meckel's cartilage (MC) robust, with subretangular corners on internal margin; posterior margin bears a prominent ventrolateral process (VTP), not contacting angular cartilages, and a robust anterolateral process (LAP).

Palatoquadrate (PQ) smaller and more slender than Meckel's cartilage, presenting a small posterior concavity, laterally limited by a small triangular projection. Ligamentary cartilage (lc) very small, positioned between both palatequadrate antimeres.

Synarcual cartilage. ( Fig. 40 a). Anterior synarcual articulates with neurocranium by a central odontoid process (OTP). Medial crest (MDC) extended over entire synarcual. Articular surfaces of the scapular process (ASP) laterally projected, separated by concavity in between. The anterior articular surface is rounded and more prominent then the posterior surface, which presents an acute extremity.

Pectoral girdle. ( Fig. 40 a). Anterior scapular process more robust; posterior process presents a small round extremity delimiting an adjacent concavity. Scapular process with a slender medial bar, with a central concavity on anterior and posterior margins, and lateral portions with a well developed central concavity. Propterygium (PRO) robust and elongated, mesopterygium (MES) small and metapterygium (MET) posteriorly positioned and elongated.

Pelvic girdle. ( Fig. 4 b). Prepelvic process (PPP) elongated, anteriorly projected. Pubosquiadic bar (PIB) slender, with expanded extremities. Modest subtriangular lateral prepelvic processes (LPP), positioned anteriorly. Laterally set, robust iliac processes (IP), presenting one round posterior expansion and a straight anterior one. Isquial process (ISP) slender, medial, and projecting posteriorly. Four well developed obturator foramina (OF).

Clasper skeleton. ( Fig. 41 ). Basal segment 1 (B1) with a wide anterior margin; both margins oval. Basal segment 2 (B2) subcylindrical with a concavity on its ventral wall. Both basal segments about equal in length, but segment 2 more slender. Axial cartilage (AX) robust, elongated and cylindrical, curved posteriorly, narrowing towards tip. Ventral marginal cartilage (VM) oval, ventrally curved. Beta cartilage (BE) slender and cylindrical, slightly dorsally curved, articulating with basal segment 1. Dorsal marginal cartilage (DM) well developed and oval, about 1/4 total clasper length, curved medially. Dorsal terminal 2 (DT2) oval, slender and curved. Terminal accessory cartilage (TA) slender and straight, presenting a narrow, curved anterior margin. Ventral terminal cartilage (VT) robust, about 1/3 clasper length, with a triangular posterior portion.

Geographic distribution. Potamotrygon garmani is known from the mid to upper rio Tocantins basin ( Fig. 43 ). Specimens were examined from five different localities (see material listed above).

Etymology. Named in honor of Samuel Walton Garman (1843–1927), an American naturalist who greatly contributed to the development of Zoology, especially Herpetology and Ichthyology, in the U.S.A. His works on sharks and rays remain among the most impressive and important contributions to the field. Garman coined the genus Potamotrygon , as well as the family Potamotrygonidae , and described five species of freshwater stingrays (three remain valid), including P. scobina .

Additional material. (10 specimens). UNT 2172 (juvenile male, 252 mm DW), same data as holotype ; UNT 2173 (subadult male, 405 mm DW), rio Santa Tereza , municipal district of Peixe , rio Tocantins, Tocantins basin, state of Tocantins, Brazil, 11°48’7”S, 48°38’21”W, coll. staff of NEAMB ; UNT 2176 (no size data), rio Tocantins , municipal district of Peixe , near the confluence with rio Santa Tereza, Tocantins basin, state of Tocantins, Brazil, 11°47’27”S, 48°37’2”W, coll. staff of NEAMB ; UNT 2177 (no size data), same data as UNT 2176 ; UNT 2179 (subadult male, 362 mm DW), rio Tocantins , municipal district of Porto Nacional, Tocantins basin, state of Tocantins, Brazil, 10°43’15”S, 48°25’14”W, coll. staff of NEAMB ; UNT 2185 (juvenile male, 273 mm DW), rio Tocantins , Tocantins basin, state of Tocantins, Brazil, coll . NEAMB; UNT 2184 (juvenile female, 226 mm DW), same data as UNT 2185 ; UNT 2186 (juvenile male, 276 mm DW), same data as UNT 2185 ; UNT 1211 (juvenile female, cleaned and stained), same data as UNT 2185 ; UNT uncat. (adult male, 404 mm DW), same data as UNT 2185 .

Figures

FIGURE 4. Teeth and dermal denticles of the holotype of Potamotrygon scobina (MCZ- 602 s, juvenile male, 238 mm DW). A. Tooth band of lower jaw. B. Tooth band of upper jaw. C. Lower jaw teeth in detail. D. Upper jaw teeth in detail. E. Denticles of cranial region. F. Dorsal tail thorns at base of tail. G. Denticles of cranial region in detail. H. Dorsal thorns at base of tail in lateral view.

FIGURE 33. Holotype of Potamotrygon garmani, sp. nov. (UNT 2174, adult? male, 341 mm DW, rio Paranã, rio Tocantins basin, state of Tocantins, Brazil). A. Dorsal view. B. Ventral view.

FIGURE 34. Paratype of Potamotrygon garmani, sp. nov. (UNT 2178, adult female, 428 mm DW, rio Paranã, rio Tocantins basin, state of Tocantins, Brazil). A. Dorsal view. B. Ventral view.

FIGURE 35. Details of Potamotrygon garmani, sp. nov. (UNT 2174, adult? male, 341 mm DW). A. Dorsal head and snout. B. Dorsal view of tail origin, pelvic fins, and dorsal thorn rows. C. Mouth and nostrils. D. Ventral view of pelvic fins, clasper and cloaca. E. Dorsal clasper.

FIGURE 36. Teeth of Potamotrygon garmani, sp. nov. (UNT 2173) A. Upper jaw (scale bar = 2 mm). B. Upper jaw (scale bar = 5 mm). C. Lower jaw (scale bar = 5 mm). D. Lower jaw (scale bar = 2 mm).

FIGURE 37. Color variation in Potamotrygon garmani, sp. nov. A. UNT 2173 (subadult male, 405 mm DW) B. UNT 2185 (juvenile male, 273 mm DW).

FIGURE 38. Scanning Electron Microscope (SEM) images of dermal denticles of Potamotrygon garmani, sp. nov. (UNT 2173). A. Dorsal rostral region. B. Dorsal rostral region in detail. C. Dorsal head region. D. Dorsal head region in detail. E. Dorsal tail region. F. Dorsal tail region in detail. Abbreviations: Bp, basal plate; Br, basal ridge; Cr, coronal ridge; Co, corona; Cd, coronal dichotomy; Cp, coronal plate.

FIGURE 39. Ventral lateral-line canals of Potamotrygon garmani, sp. nov. (based on UNT 2173) A. Overall arrangement. B. Anterior portion in detail. Abbreviations: ACH, angular component of hyomandibular canal; AJL, anterior jugular loop; AST, anterior subpleural tubules; CON, orbitonasal component of supraorbital canal; HYC, hyomandibular canal; IOC, infraorbital canal; IOL, infraorbital loop; JCH, jugular component of hyomandibular canal; JUG, jugular canal; NAS, nasal canal; NIL, nasointerior loop; PJL, posterior jugular loop; PNC, prenasal component of nasal canal; PNL, prenasal loop; PST, posterior subpleural tubules; SOC, supraorbital canal; SOL, suborbital loop; SOI, suborbital component of infraorbital canal; SPC, subpleural component of hyomandibular canal; SPL, subpleural loop; SRC, subrostral component of supraorbital canal.

FIGURE 40. Skeletal anatomy (from radiographs) of Potamotrygon garmani, sp. nov. (UNT 2178, adult female, 428 mm DW). A. Ventral view of the anterior disc, jaws and pectoral girdle. Scale bar = 15 mm. B. Pelvic girdle, pelvic radials, and base of tail. Scale bar = 10 mm. C. Angular cartilages, right side. Scale bar = 5 mm. Abbreviations: AAC, anterior angular cartilage; BCO, coracoid bar; BP, basipterigium; HYO, hyomandibula; LAC, lateral angular cartilage; MC, Meckel's cartilage; MES, mesopterygium; MET, metapterygium; MSC, mesocondyle; MTC, metacondyle; PAC, posterior angular cartilage; PIB, puboischiadic bar; PQ, palatoquadrate; PRC, procondyle; PRO, propterygium.

FIGURE 41. Illustration of the clasper skeleton of Potamotrygon garmani, sp. nov. (based on UNT uncat.) A. Dorsal view. B. Ventral view. Abbreviations: AT, acessory terminal; AX, axial cartilage; BE, beta cartilage; B 1, first basal segment; B 2, second basal segment; DM, dorsal marginal; DT 2, dorsal terminal 2; VM, ventral marginal; VT, ventral terminal.

FIGURE 42. Angular cartilages of species of the P. scobina complex. A. Holotype of Potamotrygon scobina (MCZ- 602 s, juvenile male, 238 mm DW). B. Potamotrygon scobina (MZUSP 104247, adult male, 503 mm DW). C. Potamotrygon adamastor, sp. nov. (MZUSP 104662, adult female, 545 mm DW). D. Potamotrygon limai (MZUSP 104068, juvenile male, 219 mm DW). E. Potamotrygon amazona, sp. nov. (MZUSP 117344, adult male, 532 mm DW). F. Potamotrygon garmani, sp. nov. (UNT 2174, adult? male, 341 mm DW). Abbreviations: AAC, anterior angular cartilage; LAC, lateral angular cartilage; PAC, posterior angular cartilage.

FIGURE 43. Distribution of species of the Potamotrygon scobina complex. Red circle: Potamotrygon scobina; red star: type locality of Potamotrygon scobina; purple diamond: Potamotrygon limai; yellow pentagon: Potamotrygon adamastor, sp. nov.; blue square: Potamotrygon amazona, sp. nov.; green triangle: Potamotrygon garmani, sp. nov.