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

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https://doi.org/ 10.11646/zootaxa.4310.1.1

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Potamotrygon garmani

sp. nov.

Potamotrygon garmani View in CoL , sp. nov.

( Figs. 33–43 View FIGURE 33 View FIGURE 34 View FIGURE 35 View FIGURE 36 View FIGURE 37 View FIGURE 38 View FIGURE 39 View FIGURE 40 View FIGURE 41 View FIGURE 42 View FIGURE 43 ; Tables 7–8)

Holotype. UNT 2174 View Materials (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 View FIGURE 33 ) GoogleMaps

Paratypes. (3 specimens). UNT 2173 View Materials (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 GoogleMaps ; UNT 2175 View Materials (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 GoogleMaps ; UNT 2178 View Materials (adult female, 428 mm DW), same data as holotype ( Fig. 34 View FIGURE 34 ). GoogleMaps

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 View FIGURE 33 , 34 View FIGURE 34 ). Disc anterior margin convex, presenting a small round protuberance on snout ( Fig. 35 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 35 d). Length of anterior margins of pelvic fins 19.6–25.7% DW. Claspers robust and dorsoventrally compressed ( Figs. 35 View FIGURE 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 View FIGURE 33 , 34 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View Materials (juvenile male, 252 mm DW), same data as holotype GoogleMaps ; UNT 2173 View Materials (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 GoogleMaps ; UNT 2176 View Materials (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 GoogleMaps ; UNT 2177 View Materials (no size data), same data as UNT 2176 View Materials GoogleMaps ; UNT 2179 View Materials (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 GoogleMaps ; UNT 2185 View Materials (juvenile male, 273 mm DW), rio Tocantins , Tocantins basin, state of Tocantins, Brazil, coll . NEAMB; UNT 2184 View Materials (juvenile female, 226 mm DW), same data as UNT 2185 View Materials ; UNT 2186 View Materials (juvenile male, 276 mm DW), same data as UNT 2185 View Materials ; UNT 1211 View Materials (juvenile female, cleaned and stained), same data as UNT 2185 View Materials ; UNT uncat. (adult male, 404 mm DW), same data as UNT 2185 View Materials .


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