Can someone tell me what this is?

[NastayNatron]

Vermeti snail. They let out a web to catch food particles and reel them back in. I would try and get rid of the ones you see as they multiply fast like others have said. I had them in my nano tank. I got rid of a few by puttying or super glueing there "pipe/shell" shut. I tried to pry them off the rock but they just went deeper into their shell and were impossible to get out.

Good luck!