Are these good or bad guys?

[Saltwater_hobbiest]

I have not introduced any snails in my tank and noticed two of these on my glass when my lights were off, are they good or bad?

 

[D'sreef]

See if you can pull him out and take a picture in white light. More likely than not this a good one like mini trouchus or Collonista snail ( can clog plumbing). But there is one tiny species that likes to eat zoas ( the box snail or sundial snail).

 

[Gumbies R Us]

@ISpeakForTheSeas