Is this a nudibrach or flatworm?

[aaronf30]

 

[ISpeakForTheSeas]

Looks like a nudibranch to me. Do you have any top-down photos of it (so the back is shown) under white light?

 

[Reeflix]

looks like a nudibranch but I cant say for certain...

 

[EeyoreIsMySpiritAnimal]

That's a schnauzer!

Just kidding

Definitely not a flatworm.

 

[SlugSnorter]

Looks like a nudi... and one that looks similar to that nem no less.. remove and watch for more individuals