what is this? Is it good or bad

[Joel]

I'm guessing its some kinda urchin, red coraline algae colores spines, black body with a red back? mouth?

[cyberchef]

Looks like a "pecil" urchin, but there are others on the board who would know better than I wuld... :P

[Joel]

r they good, bad, or indifferent? It is in out time til I find out.

[Alice]

That does indeed look like a pencil urchin and while they don't eat corals, they do get large and bulldoze things. If your rockwork and corals are well secured, I'd let it be for now and let it eat algae in the tank. If you don't have much algae, feed it some small pieces of nori and a sinking shrimp pellet now and then.

Alice

[Reefer Addict]

Urchins also eat coralline algae, so if you want to keep your pretty colored rocks in good shape you may not want it in your tank.
It will help the coralline spread though as it mows pieces of it off the rock, but it's your call.
Good luck.

P.S. I also agree that it looks like a pencil urchin

[sunny]

I agree looks like a pencil urchin. I had one for a short time but it really started to knock everything down so it went to a friend of mine that has it in a large fish tank and it has gotten huge. Good luck I would probably try it in there if everything is secured well.