I love hitchhikers! On
LR that is... its so exciting to see new stuff grow in your tank that you didn't intentionally put in

I had the same worm looking things on my LR when I bought it, I'm guessing you got it from a
LFS. either that a close dealer. Anyway, back to your question. Definitely get rid of the aptasia, it is the weed of coral farmers. As far as the other unknowns, I was told by very reputible folks at my LFS to let them grow to see what it is before you snuff it. I replied "well what if I can't identify it?" They all said (I ask different people on different trips there) if it's not hurting your tank, leave it be. I've had that same looking thing in my tank for almost 8 months. Every now and again when the lunar lights go own I see a pink and purple worm looking thing come out, not for very long though. I've also adopted an urchine and some very small starfish. Point is, if it poses no immediate threat to your tank, let it be and look for it, especially when its lights out!

Oh, almost forgot, they eat what slug said.