What is this on Zoas?

[Crodgers24]

Any idea what this is on my Zoas? This is the best pic I could get.

 

[vetteguy53081]

Pics a little blue. Not sure if im seeing a crab which may be an emerald or tube which may be a vermetid

 

[Crodgers24]

Pics a little blue. Not sure if im seeing a crab which may be an emerald or tube which may be a vermetid

I ended up scraping it off. Definitely seemed like a vermetid snail once I Googled it after your comment. Thanks.