O poop. I have the exact same things and Im positive they came out of my live rock (I shook them out). I left them floating at the top and yesterday I noticed they were empty ie something hatched out! Ahhhhh! Worse, last night I checked the tank in the middle of the night and I saw something about the same size as the shell scurry out of a hole, run into my snail, freak out and scurry back into the hole. It was so fast I couldnt get a a good look at it but it moved just like a cockroach. Do you think there is some underwater cockroach hybrid lol. They really are going to take over the world arent they...
