Wondering if anyone knows what these are

[Cichlid Dad]

I have live rock in my sump and have found lots of great hitch hikers. This one I can't identify. It moves on its own and pulls in if my hand gets close to them, then will come back out. I did find three brittle stars when I moved a rock last week. Sump is only maybe 2 months old.

 

[EeyoreIsMySpiritAnimal]

The white "strings"? Probably a spaghetti worm.

 

[Cichlid Dad]

The white "strings"? Probably a spaghetti worm.

Thank you