Help identify this please

[Supernova26]

Hey guys is this some kind of sps pest. they feel like small hard brown snail shells. I can't tell if its eating the sps or its growing there after the sps tissue is gone. thanks

[Smorf]

Looks like vermetid snails to me

[ToddR]

+1 on the snails

[Coral Hind]

It looks like a Spirorbis genus of worm to me. Harmless to fish and corals but can be a pain for the reefer to clean off of glass and pumps.