IMO one of the best places to find info on nudis is:
http://www.seaslugforum.net/ You can browse the database and try to find a match, or you can send in the photo and a description and Bill Rudman, or someone else working at the australia museum, will reply if they have an idea of what it might be. You might try getting some macro shots to show the detail for a better chance of ID, but nudis are notoriously hard to ID and unless they are found in their natural location and you can confirm their food source. Bill would know if anyone would.
Check out this post:
http://www.seaslugforum.net/display.cfm?id=9224 for a similar hitchhiker find, so Bill is not overwhelmed by aquarium traffic!
