Worm ID please

[Abby]

I almost dismissed this guy as a bristleworm when I saw him but decided to pull him out and get a better look, and then realized he didn’t quite look like one and has different legs. He got cut in half and I’m not sure which end this is

The fact that I can see his insides are full of sand makes me less nervous about him being a coral eater or something but still curious.

 

[Crabs McJones]

Syllid worm, I think

 

[Abby]

Syllid worm, I think

Thanks. I should have added in my original post that I found him underneath an acanthophyllia that has been struggling which we’ve been unable to find any cause for, so that’s why I was especially interested in this worm.