What is this think

[Daylilly]

It has a line of neon purple going along the middle and has two red antenas I see it moving around in my tank
I had bought a sun coral and it came on the rock with it

What is this thing should I remove it?

 

[Jon99]

Hard to tell from the pic, but maybe a sea slug?? Only problem I really see with it is it possibly dying and messing up the water a bit. Some sea slugs like the popular purple sea slug (Hypselodoris bullocki) feed on sponges. They slowly starve to death 99% of the time. There is also a possibility it may feed on coral. I'd suggest you try posting a better pic/description. Also google some photos of sea slugs and see if any are similar to what your seeing.