spikes/ denticles on ray disc

[LiuHsi]

I have seen many motoros with this spike/denticle growing on the disc, has any one seen other types of ray with this stuff ? pix?

 

[sodenoshirayuki]

http://www.monsterfishkeepers.com/forums/showthread.php?t=76537&highlight=denticle
not sure about denticles on other rays though