White mucus covering cerith snail shell openings

[M&C]

I got these cerith snails from reefcleaners last week and they haven't moved since I put them in the tank. I was sure they were dead and didn't make the trip, but I've noticed a white mucus-like layer covering their shell openings. I'm curious if they might still be alive and secreting this stuff for protection or something. Has anyone seen this before?

 

 

 

[GokesReef]

Take one out and smell it.. if it smells rotten, throw it away.