Potamotrygon scobina

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 : 59

Identification key for species of the Potamotrygon scobina complex

1a. Dorsal disc color with a reticulate, polygonal pattern, lacking ocelli; whitish blotches, when present, very small; tail with dorsal polygonal color pattern at base; dorsal tail thorns at base composed of 2 or 3 irregular rows................. P. limai .

1b. Dorsal color composed of small ocelli, few or numerous, sometimes in combination with whitish small to large blotches; tail without polygonal pattern at base; dorsal tail base with 1 or 2 rows of thorns...................................... 2.

2a. Disc relatively thin and low, head also low, not greatly elevated above disc; tail long and slender, with a well-developed terminal cartilaginous rod; distance between cloaca and tail tip usually greater or equal to disc width...................... 3.

2b. Disc relatively thick and high, head robust and elevated above disc; tail wide and robust, with short cartilaginous rod; distance between cloaca and tail tip smaller than disc width.......................................................... 4.

3a. Dorsal color gray or dark brown; dorsal ocelli usually with accessory whitish blotches; ocelli vary in size, but usually equal or smaller than eye diameter; tooth rows 40/48–50..................................................... P. scobina .

3b. Dorsal color brown to light brown, with evenly distributed ocelli without accessory whitish blotches, and relatively large, usually greater than eye diameter; tooth rows 32–40.................................................... P. garmani .

4a. Dorsal background with small, clearly separated ocellated spots with a darker contour; denticles more concentrated on central disc, disc margins relatively smooth; mean tail length 78.1% DW; tail width at base about 1/5 of disc width; dorsal tail thorns comparatively small........................................................................ P. adamastor .

4b. Dorsal background with numerous whitish spots ocelli fewer and lack a defined black contour; disc totally covered by dermal denticles; tail longer, mean tail length 86.1% DW; tail width at base about 1/6 of disc width; dorsal tail thorns well developed........................................................................................... P. amazona .