What is this?

[jstabile316]

Have been noticing these long tentacles coming out of my rocks, I still see them waving around after turning off all all pumps.

 

[Jeffcb]

Perhaps a Vermetid snail.

 

[jstabile316]

They have stripes almost look like the arm of brittle star but they get really long.

 

[Mark Goode]

It's baby Cthulhu!

Sorry, I'll get my coat.

 

[ISpeakForTheSeas]

My first thought is some kind of tube worm - no idea what kind though.

 

[JGT]

Have been noticing these long tentacles coming out of my rocks, I still see them waving around after turning off all all pumps.

Spaghetti worms. Good detritus cleaners.