I have this thin, long worm that lives in the sand along the front glass. I have never seen the end of it, but I know it is at least a foot long and maybe 1/16” across. It has black jaws that retract back into its mouth. I watched it use these jaws to pick up pieces of sand as it was extending its tunnel.
Is it an eunicid worm?
It extends the entire length of this tunnel.
You can see the black mouth parts in this picture.
And the mouth parts are retracted in this photo.
Is it an eunicid worm?
It extends the entire length of this tunnel.
You can see the black mouth parts in this picture.
And the mouth parts are retracted in this photo.

We have grown fond of him so he will probably stay for now. I am upgrading to a 75 and a 235, so he can live in this tank 



