ID help.

[Snappy]

If their web gets on corals it can irritate them if it stays there for extended periods of time.

[gobytron]

Your tank would be pretty bare if you got rid of everything that MIGHT irritate a coral.

I've also never heard of vermited snails becoming an issue as far as spreading goes....if they are, it is probably an indicator of something seriously off with your chemistry.

They are calcareous and take some time to grow.

They are also a filter feeder and help to remove debris from your water column.

I would love to see some documentation of one ever causing any long term damage to any coral...as i have only ever read about it third hand.