Slug like creature - friend or foe? [pic]

[WhiskeyCoffee]

Just discovered this hitchhiker in my tank - is he good or bad?

 

[SeaCucumberFan]

Looks like a stomatella? Can you get a pic of the other side?

 

[Reel North]

If it's a stomatella then it's good.

 

[rt67ghy]

It's a stomatella; not harmful.