Very good point,they do have similar traits,however my Marbles were from Venesuela many years ago and most as we all know come out of Colombia so the crossing of Pearls from Brasil with these marbles isnt possible.However theres some striking representatives in Brasil of Motoro so you have to say its possible.Too many people identify fish by colour only,i personally study shapes more closely....for example a Otorongo(Castexi) has a completely different disc shape to a motoro as does a Tiger Ray(P.menchacai)andFlower Ray(P.schoederi),the last two for me should be classed in a new genus.....i see striking resemblances with these two....its all about attention to detail.So back to the Pears\Motoros,as anyone noticed the the spines(denticles)that almost reach the middle of a Pearl Rays back when it reaches adulthood,i love this single row of spines that resemble large hooks,this is something ive never seen in a Motoro,ive seen random fairly large denticles appear but nothing like with the Pearls.....something to look for next time you see a large Pearl Ray.