Odd crustacean no idea if its good or bad

[larry broderic]

I bought a zoa rock and there was this strange little crustacean on it. it gobbled up a ton of hair algae so i left it alone. now i cleaned all the hair algae out and now the crustacean lets out these thin string like things and pulls it into its mouth. i has been getting bigger and bigger since ive had it. i have no idea what it is and if i should leave it alone or not.

 

[larry broderic]

l

 

[keri]

Looks like a vermetid worm(snail) to me - harmless but somewhat annoying because they "cast" their snotty-net out to catch food particles, it's somewhat unattractive and can bug your corals if they are in it's path. Some people kill them, but I'm a leave and let live'er Will reproduce in your tank, so if you're going to kill them, do it now before there are more. HTH

 

[ophiura]

But that is not what ate your algae, nor is it a crustacean. The mucus strands, as Keri described, are feeding mechanisms for a vermetid. As they are basically "filter feeders" you may get more in young tanks or those with a high nutrient load.