Cool looking, but what am I?

[ISpeakForTheSeas]

So, doing a little more research, assuming you're in the US (and assuming these came in on live rock from the Atlantic, not the Pacific), I'd guess they're a particularly attractive batch of Spondylus americanus "Thorny Oysters" - they can come in a variety of colors (including the ones yours have), they can have a widely varied number of spines (yours seem to have a high number of spines, from what I can tell), and they can have that feathering of the spines (though the one in your pictures seems to be a fairly extreme case).

So, Spondylus americanus is my updated guess.

 

[ISpeakForTheSeas]

It may also be a member of the Chamidae family (the Jewel Box Clams) - possibly Chama macerophylla. While the coloration is still somewhat unusual, it would make sense with the high level of feathering your bivalve shows.