ID these white stone looking tubes.

so i have a lot of these spawning out of my live rock. they're white tubes that can grow.
inside these tubes, these clear tentacle looking things comes out and when they sense danger, they'll retract back into the tube. the tubes look like its made out a hard substance but very fragile since i broke a couple.
here is a picture.

some said they are feather dusters but im not so sure now since i saw the tentacles retracting.

 

vermatid snails

 

i though the snails had a base, a lot of these don't have a base though. i just patched up two vermatid snails and they both had some sort of shell.

 

really.. i have tons in my tank and every once ina while i just break off as much tubes as i can. there really pesky. does it shoot out threads to catch the food?

 

actually, yea it does shoot out to catch food, with 2 tentacles. how do you get rid of these things? it's making my rocks look dusty and dirty. quite a nuisance.

 

i think you're right, they are indeed the snails.

Snails That Worm Their Way Into Tanks by Ronald L. Shimek, Ph.D. - Reefkeeping.com

are they harmless or should i get rid of them?

 

The vermetid snails I have are pretty harmless in my tank. Some people have trouble with them irritating corals but if you keep the nutrients low enough in the tank the population should stay pretty low I think and generally shouldn't be a problem. IME anyway.

 

They can annoy corals and clams.

I use kalk paste and inject the offending vermetid snails. That kills them.

 

you can also squirt some super glue gel right over them. Kalkwasser paste will work too. I just bust off all of the ones I can find once and a while. I had a bunch on my candy canes stems and they irritated it pretty bad. I also had them on a zoo frag and I always wondered why the zoos would never open. then I realized those stems were alive. I busted them off and the zoos grew over that spot. So....kill them with glue or kalk, or bust them off the rocks. Busting them will just slow them down. Maybe injure and kill a few but they will most likely grow back.

I have never seen a vermitid detract because it was scared. Your making me think you have feather dusters. They spead faster and their tubes are usually white. Most common vermitids have a red tube. Are these feathers that come out or a slime string? Vermitids have slime strings.

 

they're slime strings but over at RC, they said they are just regular worms, not vermatid. I found it weird that the two i know for sure are vermatid snails had a hard shell attached to the rock but these white tubes don't. either way, i epoxyed them up.