White nudibranch? with black antenna identification help

[Rainer W]

Hi, i need some help idenifying this critter. It's about 3/4 inch (19 mm) long and has two short black antenna. These antenna retracted momentarily when i removed it from the tank (mixed reef, mostly softies witha few hardy hard corals like birdsnests and a few encrusting corals). Is it harmful? To the best of my knowledge, nudibranches are carnivorous.
Thanks in advance for your help.

 

[wattson]

Bad guy,, not a common one but usually find them on clove or cavularia polyps. Keep an eye out for more