What is this?

[omgsaltwat]

On one of my rocks there were these little white tubes (that look like they were made of sand) that had these two clear tentacles that would come out pick up a piece of sand and go back in. and now they are on someof my other rock is this good or bad??

 

[thomas712]

My guess on the tentacles you see it may be a chaetopterid worm.

 

[reeferdawg]

are they good or bad? cuzz i have them all over the place.

 

[zanoshanox]

They are just scavengers, benefitial to the aquarium, i have tons fo them. :/
Most of mine onyl have one tentacle coming out of each sand tube though...lol

 

[thomas712]

I have many as well, usually as you described them with tubes built with little substrate pieces.