Can someone help ID whats on my trochus snail?

[mattguarino]

One of my Trochus snails has had this white mass growing on it for about a month now. It started off small near the edge and now covers more than half of its shell. It also has a small spiral growing on it too. I cant seem to find anything similar to this anywhere.

 

[PeterB113]

Most likely spongge

 

[Isopod80]

I agree. It definitely appears to be a sponge. The spiral appears to be a spirorbid worm, a harmless filter feeder. You will likely see more of these worms pop up on the rocks and glass as the tank matures. Just in case you may want to look up vermetid snails and compare the spiral. If it's a vermetid you'll want to scrape it off outside the tank. They can spread and harm corals.