Salmacis Bicolor vs. Myrionema

I haven't been around much the forum recently but I've got quite a bit of a problem with Myrionema hydroids, brown buggers are spreading rapidly along one of my rocks and I know it won't be long before they jump to the next rock.

I've read that the Salmacis Bicolor urchin is the best natural control for these guys, but I'm having a little trouble identifying this particular critter.

This appears to be a Salmacis Bicolor:
Perry's Corals & Inverts - Photo 1 - Full Version - Rate My Fish Tank - commonly known as a pink urchin.

The problem is I'm not sure how to identify this urchin, is that the only look for the Salmacis Bicolor? What defines the critter as a this particular type. My reef shop has suggested the photo attached as a bicolor urchin.

Thanks for your help.

If it's just one rock I'd un-attach the corals and move them, and then take that rock out! You don't want to have to fight those things.

Yeah, its just a hard to access rock that tends to be occupied by my sea stars.

That one in the picture looks like a Halloween urchin (Tripneustes gratilla) to me
Drs. Foster and Smith Diver's Den - Tripneustes gratilla