I've had a black longspine. Mine grew too quickly, and those spines kept my hands from the tank. It always seemed to be in the area I wanted to be in. It stuck me once, and that was enough.... If I had a 125G I think I'd get one again, but start with a tiny one. I have a collector urchin, but had to move him to my smaller tank that had less coral. It has a habit of picking up smaller frags and putting them somewhere else. I have a small tuxedo in my other tank. It doesn't carry quite as much. Right now it has a Xenia, GSP, and some macroalgae on it. I put macroalgae in the DT to supplement my california sea hare, good treat for it. I'd consider a pencil urchin, they are more compact than the spiny black, but still you'd need to make sure you have some stable rock structure, looks like he could move some stuff if he wanted. Oh, all my urchins are out during the day. I can't say they do that great of job with algae, just neat to have. I have plenty of coraline in both tanks too.
