What is this white tube/string thing?

[LordNeb]

I have been having a hard time trying to figure out what this is in my son's reef tank. They show up overnight attached to the glass, a rock, or a coral. It is a long tube or string of bubbles or eggs maybe that just waves around in the current attached only at one end. When I grab it to pull it out it is surprisingly strong and I can grab it with tweezers and pull without it breaking. They appear to be around 8 inches or more when stretched out. When I take it out of the tank it just turns to goo on the paper towel. I thought vermetid snail at first but it's not a web, just a single tube that does not react when touched.

 

[Timfish]

Larva Ceti Alpha V sand eel!?

 

[LordNeb]

In case anyone stumbles across this in the future, we have figured out what this is. A snail in the tank was really bad at attaching their eggs. It's a string of eggs that broke loose from a rock. On r plus side, it appears the snail has figured it out and the new eggs are firmly attached to a rock. Now we will wait to see if they survive long enough to hatch.