Nudibranch good or bad?

[Fish]

Hi all,
I found what looks like a "sea slug" hitchhiking on one of my zoo rocks. It's back is extremely frilly - the tassles are the size of its body, and it looks kindo of transluscent (and not colorful at all, unlike some of the ones sold in stores). I have read about 'zoo eating nudibranchs' and am wondering if this is what I have. Any thoughts? Thanks.

- Chad