Shell-less snail - good or bad?

[finksmart]

I found some shell-less snails and I was wondering if they are good or bad?

 

[kfisc]

No shell at all or upon a closer look one that's not much bigger than a finger nail? If so, probably a stomatella, which is good. If no shell at all, then the possibilites get a little darker, such as an invasion of flatworms or nudibranchs; no way to tell without a picture.

 

[o.c.d.]

Hmm, a little more of a description for a good ID might be required here. But stomatella is common so try to google that and nudibranch would be next guess. Stomatella is harmless scavenger beneficial to our aquariums.If it is a nudi a pic is in order not many are reef safe