What are these?

[polarbear]

I have a lot of these that have popped up all over my rock work in my 14 gallon biocube. They give off this stringy like mucus when messed with. I think it's some sort of worm but cant remember the name. Also are they bad for the tank? How do I get rid of them?

[Cammed_02]

Vermitid snails, they can spread pretty rapidly. They cake neighboring corals in their stringy stuff and irritate the coral enough to close up.