Hitchhiker ... any sea slug experts here?

[Merfin70]

So, the little guy came in on my live rock and has been wandering around for the last couple of weeks. I believe its a Thuridilla gracilis. I can't find out much about them so I don't know if its good or bad in my tank or what it might eat. Anyone have any info to share?

http://www.seaslugforum.net/factsheet.cfm?base=thurgrac