Livestock in refugium?

[reef bound]

If I looked real hard I could probably find something to tell me this, but I'll ask you guys instead. Is there any particular critters that a person should or could have in their fuge to make it better or more "productive"? We've got the various algae types and some snails and baby brittle stars and a couple of (I think) rock urchins, but is there something bigger we should have to make it better?
Thanks for info.

[mark]

Refugium by definition is a place of refuge so depending what you have your fuge for, guides what you could put in. Though don't think many pods make it out of mine to the display, don't think they would appreciate my 6 line wrasse joining them.