I woke up on Saturday morning, turned on the tank lights and found 23 of these on the glass that I've never seen before. My first thought was snails, but I've never had any snails in the tank, and they don't move at all. So, what sessile critters are they? Tunicates? Mussels? Barnacles? My guess is juvenile barnacles. I haven't scraped them off the glass yet and I wonder how many others are in the tank that I can't see. It is interesting how new life just pops up.
Also, I've been watching those tubes and found out that they're definitely the dancing worms that I saw. I've seen them stretching out from the tube in search of food. And, I caught them on video feeding after stirring up the tank (so it snowed in the tank as much as it did outside of my house that day):
https://www.youtube.com/watch?v=lQ3YDAcDLKw&t=9s
Oh, and remember the sea squirts video, where I thought I saw a tadpole larvae? My daughter noticed at the 8 or 9 second mark that it appears in the screen again and looks like it swims off with the tail moving! It's hard to tell, but I'd like to think that is what it is. Here's another look:
https://www.youtube.com/watch?v=gnihR5E_md8