small slugs or snails ??

[harryball69]

just noticed these small critters biggest about half an inch long and one quarter wide. looks like small slugs or a snail with a ballcap shell. there brown with a lighter tanish with black spots around their edges with a cream color underside and almost look like they have a small shell cap so to speak towards the head. i cant take a picture or i would. tank has been going for 3yrs now and ive never seen them. good or bad ? and there pretty fast too. help if u can.. thanx

 

[Squishie89]

Look up stomatella and see if that is it

 

[harryball69]

thanks.. that is them..