Sea Slug.....Is that bad??

[guinness0514]

Guys,

I bought some rock with some zoanthids on it and noticed what seems to be a sea slug on it. It was moving around on top of the zoas and looked like it was trying to eat them. Didn't see any damage and left it alone. Do sea slugs hurt anything good in the tank? Should I pull it out? It is very small at this point, maybe 2 in long.

Let me know

 

[plateboy3293]

I think their is a nudibranch that is a zoa eater try to remove it.
A pic would help.