Its some kind of boring clam. (as in rock boring) I dont know the name but I have a couple in my system too. Most of us do we just dont see them much they are usually in the rock. I was told they are not bad but could bore into a coral, not likely though.
Ive got a few in my tank. Not sure what you call them but i call them clams. Still have one that i know of, my wrasse took care of the other two. The one I have left has been on the same rock for over a year now. I was told they actually help filter the water, so I left mine. Hasnt hurt anything.
I set him on the sand in my DT about a week ago. Woke up the next morning and he was nowhere to be found. He's chillin in the back somewhere, under a rock. Doing his part to keep my water clean.