Spaghetti worm??

[BIGSKY71]

I’m wondering if this might be a spaghetti worm? If not what might it be? At first I just thought it was some random stringy stuff on the rocks, it has been in the exact same spot for months, but then I noticed there are now more of them. When I looked closely, it appeared to be moving under its own power. The central disc area of it seems to stay put, but the arms move around.
Any thoughts?

 

[BIGSKY71]

Here is a still shot