Trygon purpurea.

Dasyatis purpurea (Müller & Henle 1841)=Pteroplatytrygon violacea (Bonaparte, 1832)
Date 1841
Source Systematische Beschreibung der Plagiostomen / von dr. J. Müller und dr. J. Henle. (1841) http://biodiversitylibrary.org/item/30065#page/286/mode/1up
Author Johannes Müller, 1801-1858; Jacob Henle, 1809-1885
Source: https://commons.wikimedia.org/wiki/File:Dasyatis_purpurea.jpg

The pelagic stingray (Pteroplatytrygon violacea) is a species of stingray in the family Dasyatidae, and the sole member of its genus. It is characterized by the wedge-like shape of its pectoral fin disc, which is much wider than long, as well as by the pointed teeth in both sexes, whip-like tail with extremely long tail spine, and uniform violet to blue-green coloration. The distribution of the pelagic stingray extends nearly worldwide in tropical to warm-temperate pelagic waters.