Strange hitchhiker on my Acan

[Gmtarsw]

This hitchhike appears to have formed a calciferous shell partially obscuring one of the small Acan heads, but does not appear to be causing tissue damage, it behave like a fan worm, but has no fan just a pair of antenna, it doesnt appear to be causing any problems just curious what it is

 

[rssjsb]

It's a large vermetid snail. They're essentially harmless.

 

[Sugar Magnolia]

It's a large vermetid snail. They're essentially harmless.

Agreed. They will set out a long sticky filament when they feed which may cause the coral to retract. http://www.reefkeeping.com/issues/2005-01/rs/

 

[Geoffwehler]

Corals can definitely be effected by these snails. The stringy webs they use to catch food can irritate coral flesh. I use tweezers to crush the ones in close proximity to coral. The key is to crush larger spiral base, as this is where the actual snail lives. Fish love to eat them once crushed. I usually don't bother with the ones that are not near coral as they are not necessarily a bad critter to have. I have had some corals grow over the spiral base of the snail and then you need to break it out. In general, good filter feeders. Just keep an eye on them.