Snail/Slug thing

[Tekkors]

Does anyone know what this snail or slug type thing is and if it is bad? It has a weird pattern on it and actually moves pretty fast

 

[NightHawk]

Is it flat? I used to have a ton of stomatella snails and they look similar to that, and I haven't had issues with them.

 

[FishTV]

hard to tell from the pic, but google stomatella snail, if it is one, they're very good. They typically have a very small shell compared to the foot, and most tend to be quick

 

[NightHawk]

Stomatella snails also reproduce in aquariums, mine go crazy.They have youtube videos so you know what to look for because at first it looks like its bombing your tank with chemicals, but its really them just releasing their eggs into the water!