The whip @-@ like tail generally measure up to one and half times the length of the disc , and bear one ( more if replacements have grown in ) long , slender , serrated spine on the upper surface , closer to the base than the tip . Behind the spine , there are long dorsal and ventral fin folds that rise gradually , reaching a relatively high apex before sloping down abruptly . The presence of the upper fin fold separates this species from the similar longtail stingray ( D. longa ) , which share most of its range . However , the tail is often damaged , in which case differentiating the two species in the field become all but impossible . Young rays have completely smooth skin , while adults develop a row of low tubercles along the midline of the back , flanked by two shorter rows on the " shoulders " . The tail also become covered in prickles . This species is a uniform olive to brown to gray above , darkening to black on the tail , and off @-@ white below .