ETA: Oops, my bad. I didn't see the pics on the second page
glad they were ID'ed though!
Deanna
I believe that these are from the tunicate family. I have similar looking ones in my tank that came on my live rock. They were almost transparent with a bright greenish yellow ring around the top. They seem to come and go. I had no idea what they were until I saw a pic of them from another web site. Search on google images and you can see some of the many different types there are.
Deanna