Under Stingrays , a rare specimen would be the P Garrapa
I have never seen anybody have one in their private collection although
in japan there may be a pic that could be a garrapa
Here are some pics ..
Heres a Close Up Pic of A Garrapa
A Garrapa Versus a Henleii
Finally a Japanese website with a Garrapa
It could very well be that this stingray is a particular morph of one of the black rays
or a hybrid , but since i havent read any literature proving that, i will count the Garrapa as one of the rarest rays.