Snails?

I would not be immediately worried about it, unless you can see marks where they have been chewing on the Zoanthids.
If I recall correctly in the other thread, the Zoanthids have been retracted lately. This often happens because of a biofilm of bacteria and algae growing on them.
Snails are great cleaners.
Most snails eat algae. If there is a lot of tasty algae growing on the polyps, that would be the reason for the Collinista Snails partying on the Zoanthids. Just for fun, we can say that Cyanobacteria is a "Combo Meal" of algae and bacteria in one.
I would take an old toothbrush and give the Zoanthids a good brushing. Don't worry, they are very tough skinned. They actually love it and usually come out bigger and better than ever after the cleaning.


Edited by Mark Peterson - November 26 2010 at 9:33pm

Almost all snails are nocturnal.
When the amount of snails and the amount of available food(algae) is in balance a tank might have hundreds of snails but only a dozen will be seen during the brightest part of the day.
Have you noticed the movement that occurs in the tank during the twilight hours of dusk and dawn? Fish are heading for bed and snails are waking up.

One possible but unlikely concern here is that something more serious is going on with the Zoanthids. If, when brushed, the Zoanthids seem to be disintegrating, brush a little softer and let us know here. Then, if you can, check the Alk and Ca and post a pic of the tank.