what is this?

[RedLeggedHermit]

i just noticed this thing in my refugium. its kind of transparent with a flexible, round head that it flattens against the glass and then closes to catch food.it has a scissor like tail. what is it and is it good or bad?

 

[ccCapt]

It's a flatworm. Some are harmless, some are coral eaters. If you see 1, chances are you have more. I would remove it if possible.