Common names
Great freshwater stingray, Raia preta do Tocantins

Short Description
Original diagnosis after DE CARVALHO, 2016 [24368]: A large, bulky species of Potamotrygon endemic to the middle and upper rio Tocantins, diagnosed by the following unique characters: blackish to blackish-brown dorsal color with intense yellow to orange spots (generally smaller than eye-diameter), usually forming distinct concentric clusters on dorsal disc and tail (clusters larger on central disc, smaller towards disc margins and on dorsal tail) separated by slender reticulate pattern of dark background color, usually with larger ocellate spots at center of clusters on posterior and outer disc, and with spots sometimes coalescing to form vermiculate shapes; ventral color dark gray to dark brown, with creamy white spots (smaller than eye-diameter) on central disc, pelvic fins and more numerous and smaller on ventral snout region, with a creamy white vertical streak over gill slits and anterior pelvic fins in most specimens, and sometimes with a creamy white snout and/or nasoral region. Other characters in combination that further diagnose P. rex, sp. nov., include: pelvic fins with broadly circular apices (also present in P. henlei and P. leopoldi, but these species lack bright orange spots forming concentric patterns on dorsal disc and usually have a lighter ventral coloration); absence of distinct labial grooves (strong grooves at least in P. constellata, P. orbignyi, P. humerosa, and P. marinae); an irregular double row of slender, sharp, not too numerous, and moderately erect to raked thorns on dorsal tail (P. leopoldi with three to four rows of closely packed, slender and evenly distributed thorns); presence of two angular cartilages, first angular anteriorly concave and well calcified, posterior angular less calcified, more slender, and not anteriorly concave (single angular present in P. tigrina, P. schroederi, P. constellata, P. magdalenae, P. histrix, P. schuhmacheri, P. orbignyi, P. humerosa, P. marinae, and P. wallacei; anterior angular wide and posterior angular absent or very small, abutting hyomandibula, in P. signata, P. pantanensis and P. amandae; anterior and posterior angulars present in addition to a small lateral element in P. limai and P. scobina).

Distribution
endemic to the middle and upper Rio Tocantins, Brasilia [24368]

Biology
Diet: fishes, insects and insect larvae, mollusks, and crustaceans, with a predominance of insect larvae. [24368]

Size / Weight / Age
male (max, paratype): 825 mm TL, 526 mm DL, 475 mm DW), female (max, holotype) 1110 mm TL, 750 mm DL, 690 mm DW [24368]

Habitat
benthopelagic; freshwater [24368]

Dentition
Teeth set in quincunx, in 21–44/20–47 total rows (n = 14); largest female (holotype) with 44/47 (with 25/18 exposed tooth rows with mouth closed, just slightly covered dorsally by nasal curtain); largest male with 31/33 tooth rows (with some 14/10 exposed tooth rows with mouth closed). Teeth low, rather flattened in females and with slightly higher, more elevated crowns in larger males, but generally without very sharp, pointed cusps; teeth hexagonal to rhomboidal, usually broader than long. Teeth in midlateral rows slightly wider in upper tooth band. [24368]

Remarks
shark-references Species-ID=14688; CITES: (see: Protected Species for more details) Convention on International Trade in Endangered Speciesof Wild Fauna and Flora annex: III; Council Regulation 2017/160 annex: C