Some weird tentacle things coming out of rock

Here's the picture.
Basically looks like a bunch of little arms.
ONLY comes out at night, and whenever any light is on it, it retreats into the rock
It's usually bigger than that, almost twice the size. Not anything like a brittle star

 

It looks like a spaghetti worm.
It is a detritus cleaner so it would be a good addition to your tank.

 

I agree, spaghetti worm.

 

It's hard to tell.
I looked at it again later on, and I could actually see small little black specks on the tentacles, like a brittle star might have.

However, I don't think its a spaghetti worm after looking at pictures.
These tentacles are a bit bigger

 

Then it sounds like a mini brittle star. Which is a good hitch hiker.