Potamotrygon amazona, 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 : 33-43

Potamotrygon amazona , sp. nov.

( Figs. 24–32 , 42 , 43 ; Tables 5–6 )

Holotype. MZUSP 117344 (adult male, 532 mm DW), rio Jutaí , municipal district of Boca do Titica, upper rio Amazonas Basin, state of Amazonas, Brazil, 2°55’24.8”S, 66°57’07.6”W, September 2012, coll. F. Marques et al. ( Fig. 24 ).

Paratypes. (2 specimens). MZUSP 117346 (adult female, 405 mm DW), same data as holotype ( Fig. 25 ); MZUSP 117348 (adult male, 494 mm DW), same data as holotype.

Diagnosis. Potamotrygon amazona sp. nov. is distinguished from congeners, except P. limai , P. scobina , P. garmani sp. nov., and P. adamastor sp. nov., by a combination of characters: disc relatively thick and robust, with a dark brownish to gray dorsal color, covered with numerous whitish to beige irregular spots, with small ocelli sometimes present; disc completely covered by denticles, with a high concentration of denticles on rostral portion of disc; rostral denticles simple, with a single central crown, and star-shaped basal plate; head denticles present star-shaped crowns, with a well-developed anterior dichotomy and small lateral dichotomies; caudal denticles with a central coronal plate and two anterior dichotomies, and a star-shaped basal plate; three angular cartilages of different sizes between jaw and hyomandibula; two to three irregular rows of thorns on dorsal tail midline, varying in size; tail long and robust, very prickly; tail base wide; cartilaginous rod relatively short. Potamotrygon amazona sp. nov. is further separated from P. limai by not having any polygonal pattern over disc, by having a wider tail (16.7% DW vs. 14.8% in P. limai ), and by having simpler dermal denticles (smaller number and size of coronal ridges). From P. scobina and P. garmani sp. nov., P. amazona sp. nov. is distinguished by having a considerably more muscular disc, a more intense concentration of denticles on disc, dorsal color with many more spots, and a wider and shorter tail (mean tail width 14.9% DW vs. 13.4% DW in P. scobina and 14.1% DW in P. garmani sp. nov.; mean tail length 86.1% DW vs. 121.5% DW in P. scobina and 100.6% DW in P. garmani sp. nov.). Finally, P. amazona sp. nov. is separated from P. adamastor by having more dermal denticles on disc, greater number of dorsal spots forming clusters, and a longer tail (mean tail length 86.1% DW vs. 78.1% DW in P. adamastor ).

Description. Disc subcircular, longer than wide (DL 101.9–107.3% DW) ( Figs. 24 , 25 ). Rostral portion of disc broadly convex, presenting a small rounded protuberance on snout ( Fig. 26 a). Disc robust, dorsoventrally compressed, with comparatively thick margins. Eyes small and oval, around 3 times smaller than spiracles. Spiracles rhomboidal ( Fig. 26 a), presenting a central internal papilla. Large and dorsally elevated head, up to 1/3 disc length, with interorbital distance 14.4–17.8% DW, and interspiracular distance 15.4–18.3% DW. Nasal curtains partially covering mouth, except at its margins. Mouth small and slightly convex, with a central notch (mouth width 8.5–10.2% DW, and internasal distance 7.5–8.6% DW) ( Fig. 26 c). No labial ridges present. Five buccal papillae present, two posterior alternating with three anterior. Branchial basket wider than long, with space between first branchial slits 25.3–28.1% DW, and distance between fifth branchial slits 17.4–18.9% DW.

Teeth small and numerous, wider than long, set in quincunx in a narrow arched upper tooth plate and a wide and trapezoidal lower tooth plate ( Fig. 27 ). Tooth rows varying from 52–56 in upper jaw and 48–58 in lower jaw in males; single female specimen counted with 44 teeth in both jaws. Adult males present a single central pointed cusp on teeth in center of tooth plate. Lateral teeth in adult males, juvenile male examined, and female simple, presenting a single rounded cusp.

Pelvic fins broad (length 54.3–64.9% DW), subtriangular, with rounded corners and a slightly undulated posterior margin. Pelvic fin posterior margin barely projects beyond disc ( Fig. 26 d). Length of anterior margins of pelvics 23.6–26.9% DW. Claspers robust and cone shaped; clasper base much more robust and wider than its rounded tip; clasper external length 9.6–12.0% DW and internal length 17.0–19.5% DW. Clasper groove long, slightly curved, with a semicircular apopyle, at level of posterior tip of pelvic fins; hypopyle oval and large, subterminal, anterior to clasper flap. Dorsal pseudosiphon oval, obliquely positioned ( Fig. 26 e).

Tail robust and long, tail width 12.9–16.0% DW. Tail tapers more intensely from caudal sting origin ( Fig. 26 b). Cartilaginous rod short and robust, around 1/3–1/4 tail length. Caudal sting origin relatively close to tail origin. Tail with numerous lateral denticules, but without defined lateral spine rows. Small dorsal and ventral folds on tail extremity. Caudal stings well developed, their length 16.6–19.2% DW.

Coloration. ( Fig. 28 ). Dorsal disc brownish gray to olive, with numerous small irregular spots from white to yellow, covering disc, sometimes with small ocelli (especially on disc margins), but these without a defined black contour. Two overall patterns apparent concerning spots and ocelli: 1) disc covered with small irregular whitish spots, smaller and more numerous on central disc, not forming definitive patterns; with small oval spots present on disc margins, smaller than eyes but larger than most irregular spots; 2) smaller irregular spots present, more spaced apart, forming semicircular or circular patterns, sometimes with ocelli at center. Spots progressively larger from disc center to margins. Dark streaks on head, synarcual, pectoral girdle and tail base present in both patterns. Ventral disc white to beige, sometimes with a darker central blotch. Larger specimens sometimes with darker pattern on lateroposterior disc margins, not anterior to central disc. Intensity of dark pigmentation increases with age and size. Pelvic fin dorsally with same color pattern as disc margin, with a slender lighter posterior margin. Ventrally, pelvic fins whitish with a posterior dark margin, varying with specimen size and age. Claspers also whitish but with darker gray blotches. Dorsal tail dark, similar to disc. Tail sides with small groups of small whitish irregular spots, without ocelli. White irregular blotches sometimes present between smaller spots. Ventral tail light with dark blotches, continuous with those of disc; whitish blotches interspersed with darker ones.

Dermal denticles. ( Fig. 29 ). Disc covered with dermal denticles, but more numerous and developed in three different regions. Rostral region presenting simple denticles, greatly varying in size (up to 3–4 times), with a single pointed crown. Basal plate (Bp) barely apparent, with asymmetrical basal ridges (Br) varying in number from 5–7. Rostral denticles arranged in a semicircular pattern on disc. Head and central disc with star-shaped pattern, presenting a developed central coronal plate (Cp), with two lateral posterior ridges and two converging anterior coronal ridges (Cr), these in two levels ( Fig. 29 d). Single and double terminal dichotomies sometimes present. Basal plate poorly developed. Caudal region presenting a central well-developed coronal plate, curved posteriorly, with two anterior coronal ridges. Basal plate well developed, with 2–6 basal ridges. Two to three thorn rows on tail, varying in size, robust and curved posteriorly, with a marked basal plate.

Ventral lateral-line canals. ( Fig. 30 ). Hyomandibular canal (HYC) extends anteriorly from nostril, turning abruptly toward outer disc margins, extending parallel to anterior margin of disc. Anterior subpleural tubules not observed. Hyomandibular canal extends posteriorly as the subpleural component of hyomandibular canal (SPC), slightly undulated. Subpleural loop (SPL) deflects abruptly interiorly just anterior to level of pelvic fins; posterior subpleural tubules absent. Jugular component (JCH) projects anteriorly with a slight undulation towards branchial basket. Angular component of hyomandibular canal (ACH) runs external to branchial slits, and turns interiorly to the jugular canal (JUG) anterior to the branchial basket, reaching the posterior jugular loop (PJL). From this loop, the infraorbital canal (IOC) turns externally to form infraorbital loop (IOL). The infraorbital canal extends anteriorly, with slight undulations, curving toward disc center, forming the suborbital loop (SOL). Supraorbital canal (SOC) extends anteriorly from the anterior jugular loop (AJL). Orbitonasal component of supraorbital canal (CON) extends towards nostrils forming prenasal loop (PNL). Nasal canal (NAS) short and straight, directed toward mouth from anterior jugular loop. Prenasal component of nasal canal (PNC) extends towards anterior snout from anterior margin of nostrils.

Measurements N Holotype Range Paratype Range Mean SD Skeletal morphology. Neurocranium. Nasal capsules (NC) ventrolaterally expanded, their anterior margin rounded, with an internal ventromedial sept in between ( Fig. 31 ). Precerebral fontanelle (PCF) wide and subcircular, with straight anterior margins, posteriorly delimited by a subtriangular epiphysial bar (EBP). Frontoparietal fontanelle (FPF) subtriangular, narrowing posteriorly, extending to level of anterior margin of postorbital processes; fontanellae together keyhole-shaped. Postorbital processes (POP) prominent, long and narrow, projecting anterolaterally to posterior angular cartilage. Prespiracular cartilage (PSC) posteriorly curved.

Jaws and hyomandibular arch. ( Figs. 31 a, b). Hyomandibular arch (HYO) elongated and anterolaterally projected, slightly curved anteriorly. Three angular cartilages present. Anterior angular cartilage (AAC) slightly concave, about 1/5–1/4 length of hyomandibulae. Posterior angular cartilage (PAC) more straight, slightly smaller and more slender than anterior angular cartilage. Lateral angular cartilage (LAC) subcircular, between posterior angular cartilage and hyomandibula, about 1/4–1/3 length of posterior angular cartilage. Meckel's cartilage (MC) robust, internal margin with subretangular corners; its posterior margin bears a prominent ventrolateral process (VTP) not contacting angular cartilages, and a robust lateroanterior process (LAP). Palatoquadrate (PQ) smaller and more slender than Meckel's cartilage, presenting a small posterior concavity laterally limited by a small triangular projection. Small ligamentary cartilage (LC) present between palatoquadrate antimeres, not fused to antimeres. Synarcual cartilage. ( Figs. 31 b, c). Anterior synarcual articulates with neurocranium by a central odontoid process (OTP). Medial crest (MDC) extends over entire synarcual. Articular surfaces of scapular processes (ASP) laterally projected, separated by concavity in between. Anterior articular surface rounded and more prominent then posterior surface; posterior surface with an acute extremity.

Pectoral girdle. ( Fig. 31 c). Anterior process of the pectoral girdle robust, posterior process with a small rounded extremity delimiting an adjacent concavity. Scapular processes with a slender medial bar, presenting a central concavity at anterior and posterior margins; lateral portions of scapular processes with a well developed central concavity. Propterygium (PRO) robust and elongated. Mesopterygium (MES) small and mesocondyle (MSC) elongated.

Pelvic girdle. ( Fig. 31 e). Prepelvic process (PPP) very elongated, almost reaching pectoral girdle. Pubosquiadic bar (PIB) slender, with expanded extremities. Lateral prepelvic processes (LPP) subtriangular, positioned anteriorly. Laterally positioned, robust iliac processes (IP) presenting a single round posterior expansion and a straight anterior one. Isquial processes (ISP) slender, set more medially, and projecting posteriorly. Four relatively large obturator foramina (OF) present.

Clasper skeleton. ( Figs. 31 d, 32). Basal segment 1 (B1) with a wider anterior margin; both margins oval. Subcylindrical basal segment 2 (B2) with a concavity on its ventral wall. Both basal segments about equal in length, but segment 2 more slender. Axial cartilage (AX) elongated, cylindrical and robust, curved posteriorly, narrowing toward extremity. Ventral marginal cartilage oval (VM), ventrally curved. Beta cartilage (BE) slender and cylindrical, slightly dorsally curved, articulating with the wall of basal segment 1. Dorsal marginal cartilage (DM) well developed and oval, about 1/4 of clasper length, curved medially. Dorsal terminal 2 (DT2) oval, slightly slender and curved. Terminal accessory (TA) cartilage slender and straight, with a narrow, curved anterior margin. Ventral terminal cartilage (VT) well developed, about 1/3 of clasper length, being the most robust posterior element; ventral terminal with a triangular posterior portion, curved dorsally.

Geographic distribution. Potamotrygon amazona is described primarily from the rio Jutaí basin, state of Amazonas, Brazil ( Fig. 43 ), but other specimens identified as P. amazona are known from rio Branco (Roraima state) and rio Juruá. However, these localities may be innacurate, especially the latter as the specimens examined had poorly preserved tags and lack more precise locality information.

Etymology. Potamotrygon amazona sp. nov. is named after the female warriors of Greek mythology, the Amazons, daughters of the god of war and goddess of harmony. Gender feminine.

Additional material. (6 specimens). MZUSP 117347 (adult male, 560 mm DW), rio Jutaí , municipal district of Boca do Titica, upper Amazon Basin, state of Amazonas, Brazil, 2°55’24.8”S, 66°57’07.6”W, September 2012, coll. F. Marques et al. ; MZUSP 117345 (adult male, 584 mm DW), same data as 117347 ; INPA uncat. (“no tag1”) (juvenile male, 465 mm DW), rio Juruá , " Boca do Anaxaqui, Uacari " ; INPA uncat. (“no tag2”) (adult male, 525 mm DW), same data as INPA “no tag1” ; INPA uncat. (“no tag3”) (adult male, 531 mm DW), same data as INPA “no tag1” ; INPA 7911 (adult male, 524 mm DW), rio Branco , municipal district of Comunidade Sacaí, state of Roraima, Brazil, 1°23’46”S, 61°50’40"W.

Figures

FIGURE 24. Holotype of Potamotrygon amazona, sp. nov. (MZUSP 117344, adult male, 532 mm DW, rio Jutaí, upper rio Amazonas basin, state of Amazonas, Brazil). A. Dorsal view. B. Ventral view.

FIGURE 25. Paratype of Potamotrygon amazona, sp. nov. (MZUSP 117346, adult female, 405 mm DW, rio Jutaí, upper rio Amazonas basin, state of Amazonas, Brazil). A. Dorsal view. B. Ventral view.

FIGURE 26. Morphological details of Potamotrygon amazona, sp. nov. (MZUSP 117344, adult male, 532 mm DW). A. Dorsal head and snout region. B. Mouth and nostrils. C. Dorsal view of tail origin, pelvic fins, and dorsal spine rows. D. Ventral view of pelvic fins, claspers and cloaca. E. Dorsal clasper.

FIGURE 27. Teeth of Potamotrygon amazona, sp. nov. (MZUSP 117345) A, B. Upper jaw. C, D. Lower jaw. Scale bar = 2 mm.

FIGURE 28. Color variation in Potamotrygon amazona, sp. nov. A. MZUSP 117347 (adult male, 560 mm DW). B. MZUSP 117345 (adult male, 584 mm DW).

FIGURE 29. Scanning Electron Microscope (SEM) images of dermal denticles of Potamotrygon amazona, sp. nov. (based on MZUSP 117345) A. Dorsal rostral region. B. Dorsal rostral region in detail. C. Dorsal head region. D. Dorsal head region in detail. E. Dorsal caudal region. F. Dorsal caudal region in detail. Abbreviations: Bp, basal plate; Br, basal ridge; Cr, coronal ridge; Co, corona; Cd, coronal dichotomy; Cp, coronal plate.

FIGURE 30. Ventral lateral-line canals of Potamotrygon amazona, sp. nov. (based on MZUSP 117345) 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 31. Skeletal anatomy (from radiographs) of Potamotrygon amazona, sp. nov. (MZUSP 117344, adult male, 532 mm DW). A. Ventral view of anterior disc and jaws. B. Angular cartilages, left side. C. Pectoral girdle, ventral view. D. Tail thorns and clasper skeleton. E. Pelvic girdle and clasper. Scale bar: 10 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 32. Illustration of the clasper skeleton of Potamotrygon amazona, sp. nov. (MZUSP 117347, adult male, 560 mm DW). 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.