Hey guys, I’ve discovered a new critter in my sump. I haven’t gotten any new live rock in years and I transferred this from a different tank to sit in my sump. I was looking closely at some baby cardinal fish down there when I noticed something retract on the rock. The way it moved, It resembled a goby moving back into its hole. Upon further inspection, I’m completely lost. When it’s shut, it has a hard shell, I tapped it with some tweezers. When it opens up, (it opens toward the camera, black face folds down) I can’t even tell what I’m looking at. Also, there is a tentacle hanging in front of it when open that disappears when it retracts. It hasn’t left the hole but I’m convinced it’s nocturnal as about 30 seconds after I turn the light on, it retracts. (Or it can see me...) Any ideas would be much appreciated.