Nighttime slugs with shells

[danberger]

Hey all, looking to ID these guys. Found two of them at night coming out of the rocks. They look like slugs but have a hard shell. When we tried to grab one it released some sort of cloud… See below.

 

[fishguy242]

stomatella snails, good guys...

 

[Nano sapiens]

Stomatella snails. Good algae eaters that often reproduce in a reef aquarium.