What kind of slug or snail is this?

[FreshSaltyGuy]

So any idea what this? It moves like a slug with something that looks like a integrated shell. I didn't don't buy it so must have come on my live rock.
Good or bad?

 

[WheatToast]

Stomatella snail. These are common hitchhikers that are often confused with snails due to their reduced shells. They are good algae grazers and will reproduce over time. Beige Stomatella without patterning are most common, but pink, black, and striped snails also show up from time to time.
http://www.wetwebmedia.com/MolluscPIX/Gastropods/Prosobranch PIX/Limpets Scutus/stomatella varia.JPG

 

[FreshSaltyGuy]

So any idea what this? It moves like a slug with something that looks like a integrated shell. I didn't don't buy it so must have come on my live rock.
Good or bad?

Here is another pic and video. It seems to be eating the algae on the live rock so seems beneficial. Just want to be sure ok for Corals.

 

[WheatToast]

Here is another pic and video. It seems to be eating the algae on the live rock so seems beneficial. Just want to be sure ok for Corals.

"Look at this distinguished gentleman. Look at the way he is sitting. Yes, very distinguished. Mm-hmm, I see!"
I have never heard any reports of them becoming an issue in captivity.