Tiny snail...is this a friend or foe

[Sticker shock]

Found a small group of these guys crawling around my zoa's last night. These zoa's also happen to be slowly disappearing. When I turned on the light, the snails scurried into the rock to take cover. I'm hoping they might be baby nassarius, and are not the cause of my zoa issues, but whats the expert opinion on these guys?

 

[PokeFish]

Foe i think. I am pretty sure there is a tiny snail that can go onto other molusks and kill them. Might not be this one though