What are these on my Astrea snails?

[Jhoekstra84]

I noticed these on my astrea snails. I had an algae outbreak prior to me noticing them, so I couldn’t see them before. They retract into the black cone when touched.

 

[Wallace11]

Looks like vermatid snails. You can carefully snip them off at the base with scissors or bone cutters making sure not to damage the snail shell.