Purple Flatworm?

[Court_Appointed_Hypeman]

Picked this little guy off my first coral, he is still alive in a small container of old tank water.

Its bad right?

If its a good guy, he's pretty and I would like to throw him in the tank.

 

[Cthulukelele]

He moves like a very young polyclad flatworm. There are lots of types--some harmless most not. They range from benign to coral and fish munching nocturnal assassins depending on the species. Hard to say.

 

[Cthulukelele]

Alternatively, if it is rust colored under your lights and has 2 little "horns" it's red planaria, the most common flatworm in the hobby. Mostly benign but replicates like mad. If you have wrasse then they're free food. If not, then can sometimes grow to biblical proportion. Not usually a direct coral threat though.