Weird tube like think on rock

[Klewtz]

I recently got a small piece of live rock from my LFS and noticed today I have a small little tube thing on my rock. It is a little hard and can not remove on my own. As I was holding it out of the water it slowly moved more into the rock. I put it back in the water and went to look for it again later and it was gone. I’m assuming it went back into the rock and is chilling in there. Does anyone know what this could be and or if it’s bad or good?

 

[ISpeakForTheSeas]

Any chance you can get some pics of it under brighter, white light? My first thought from the pics would be a peanut worm (Sipunculan) or similar, but that doesn't match the description.