What is this?!

[Dbar365]

The light in my tank had been off for a few hours. When I turned them on I saw this guy moving around on my rocks. What is this. Is it dangerous to my tank?

 

[Oscar lover 98]

The light in my tank had been off for a few hours. When I turned it on I saw this guy moving in too if one of my rocks. What is this. Is it dangerous to my tank?

It looks like a sting ray or maybe a slug ?

 

[mistersprinkles]

It looks like a sting ray or maybe a slug ?

Not a stingray...

 

[BelleMorte]

That is neat looking

 

[Mebbid]

Most likely a nudibranch of some sort