What is this?
 

Found this worm looking thing under a rock. Just curious what it is and if it's bad?

Dark picture, but it looks like a bristle worm. If its pinkish and looks sorta like a centipede then definitely a bristle worm and not bad at all. Great detritus eaters and general scavengers... Just don't touch it ;)

It is a bristle worm guaranteed if you have one you will have a lot more not seen vast majority are harmless and make a great CUC however never handle them bare handed as their bristles will give you anywhere from a mild jolt to full on pain.

2 species not generally accepted as being safe in your system are fire worms and enucid worms both are easily identifiable.

I personally am not a fan of bristle worms but I have way too many so I have learned to live with them

Thank you. That's exactly what they are. Thank you for all the information

They are the maggots of the SW sand world. I never had them once I removed the sand bed.

I thought the same thing until they took out my prized Cook Island Maxima.