Some help with "ID ing" a potential pest

[mustangtjb]

Whatever this is it throws off tentacles when it gets pissed off. It's the brown shell looking thing at the front of the tile.

I'm likely gonna scrape it off but figured I'd ask just the same.

Thanks in advance.

 

[Chris A.]

It’s harmless but can multiply and can Irritate corals
I just superglue them shut or scrape them off

 

[tommy6905]

Vermitid snail and what Chris said

 

[Shooter-McGavin]

I'd be careful with any stonies you have, I'm pretty sure they affect them.

 

[Matt Kiely]

Definitely a vermitid snail