ID Please- Sucking on Acro

[Reggae Fish]

I found this on an acro today...

What is it?
Is it bad?

Thanks for your help!

 

[bigmayreefer]

hopefully they arent bad cause i got tons of em in my tanks. have never seen em on my corals tho.

 

[Reggae Fish]

Mine doesn't seem to like light

 

[Chelsey]

I think it's a stomatella, not bad.

 

[Sk8r]

If it's a stomatella it's very differently shaped than any of mine, which look like a garden slug with a tiny shell saddle midway.

 

[DrBDC]

If you mess with it's back does that white spot get larger?