Help identify

[no1bubba]

Have found several of these growing in tank. Is this a bad thing? It is hard to see but they appear to be short black spikes.

 

[Vinny Kreyling]

AHH The dreaded Vermetid Snail.
They can become a plague Or they can stay small.
No known predator that is reef safe & best way to kill them is to break as close to base as possible then glue over.