Can anyone tell me what this is?

[Usatennisfan]

Any livestock go missing on occasion? I had a bobbit worm in my tank once and when I found his lair it was just a big pile of slime like that.

 

[JMSKI333]

Vermetid snail webs?

+1 it's vermetid snails. Same thing happens in my tank (not as bad). They are harmless for the most part but you must have a dense population of them on that one rock.

 

[Muney Mun]

Just looked up bobbit worm and pray and hope that's not what I got. That thing is terrifying. That slime is on the bottom of all my rocks so I hope that isn't lairs everywhere