is this agood or bad urchen
 

i got this as a hitch hiker on some live rock and was wondering if it was possibly one of the ones that eat coraline algae
He is black with short brown pointy spines with white tips at the base of the spines is a white ring with a bright blue.

There good ,mostly eat coraline algae. They will though rearrange your coral if they are not attached.

Looks like a math urchin. Rock boring species that chews a burrow into rock. Eat macroalgae and pellets, probably won't do much to the coraline.

http://www.scuba-equipment-usa.com/m..._mathaei).html

thanks all though not as spiny as the one in the picture i think that's it.
so I guess the question is should he go or can he stay

I'd leave him. I have one I paid $20 for at the LFS, LOL. I bought him because they will eat caulerpa and I had a bit that I couldn't remove manually very easily. He took care of that. Mostly he just sits there and does nothing, he's not like the tuxedo urchins that dress themselves with anything that they can pick up.

cool thanks :becky:

Looks like the one I've had in my tank for about four years with no problems. Knocks things down once in a while but does not make any real trouble. It hides during the daytime and roams around only once the lights are out.