Vermetids

A.K.A. “Spider-Snails”

Learn more about vermetids:

Here is a quick rundown of vermetids on Wikipedia: https://en.wikipedia.org/wiki/Vermetidae

Here is a brief, but in-depth article on vermetid effects on corals: http://rsbl.royalsocietypublishing.org/content/early/2010/05/18/rsbl.2010.0291.full (this comes directly from the scientists [in this case, my friends] to you)