need help identifying these

[ashell]

Hi all,

Just picked up my rock from the LFS, and noticed several hitchhikers that are alive as of now. I've looked and looked, but can't figure out what these are and if they are harmful or not. they look like a small bunch of pebbles(almost like a cocoon) with a long white tentacle or two reaching out. Any help is appreciated. here is a pic

Thanks,

 

[MableShwartz]

Might be a type of worm?

 

[bonomo53]

looks like spaghetti worms, there good they will catch left over food particles