ID: Hitchhiker nudibranch, or less likely, a flatworm?

[Tunguska]

I would like to know what this little guy is and what it eats if anyone knows specifically. I suspect it is a nudibranch, but I'm not certain. I found it in my refugium tonight while removing some of the cheato. I've got 9 pics in my gallery if this one isn't sufficient for ID. I have not added anything since at least August, so it has been getting plenty to eat in an algae filled refugium that gets some cyclopeze every now and then. Thanks for the help.

 

[LeslieH]

It's a common flatworm in reef tanks & it preys on molluscs. Either this species can go for long periods of time without eating or it can survive on non-preferred food items. Not a good tank inhabitant if you plan to have molluscs as part of a cleaning crew.

 

[Tunguska]

Thanks for the ID.