I have had this live rock for over a year now, and this one rock with what appeared to be just a old shell, like a mussel or something had been there before it was taken out of the ocean, has always been in the foreground of the tank. Well today I was just string at some pods
that were crawling around on this shell and when one tried to enter the shell, the thing closed up and moved itself deeper into the rock! Then a second later it pushed itself back out and open up.
I am trying to figure out what this is. Here are sme clues for you experts out there. Small, maybe an inch. Tear drop shaped shell. White/green with brown spots, like a chess board pattern.
If anyone knows, please post!