critter id

I have had a montipora cap and montipora seasons greetings (undata?) recently die very suddenly when they were thriving previously and growing to new rock. I have acropora right next to the montipora that continue to thrive. I remember reading something about montipora eating nudibranchs...

This came attached to a new chalice frag. I had guessed because of the tube I needed to dip more than once so closely supervised them being dipped. But after several days I haven't seen anything until tonight. So what is it? Do I need to try and manually remove it or re dip? Or can I leave it...