Can you all help me identify these little creatures and let me know if they are good or bad? I recently purchased some live rock and it is brimming with worms, like the one pictured below, and small yellow starfish. One of the rocks also had the slug like thing that I have pictured below.


The slug like thing was pretty cool. When it is on a rock it is completely flat, as is shown on the picture. At first I didn't notice it. I actually didn't notice it until it started moving towards the top of the rock. Once it got to the top of the rock it seemed to stand on its two longest sides. (It looked like a piece of paper would look if you stood it on its two longest sides.) After it got to the top it started excreting some stuff from a small white tip. The stuff that it was excreting looked like microbubles, but I it could have been something else.
Any help anyone can give me on identifying these little creatures is greatly appreciated.