Little hair like worms in clusters

[jeffrey750750]

I have these in many spots on the rocks but noticed this cluster in the sand after lights out. Not worried about them, I just don't know what they are?

 

[Crabs McJones]

Spaghetti worm. It's actually one animal. What you're seeing are the tentacles it uses to find food. Beneficial and eats leftover food and detritus. Cool find!