i just baught a clam and as i put it in my tank i looked at the bottom of it and it is open like a hole there. is this where the foot is and where it attaches itself to things? there is a small rock attached inside the opening should i pull the rock out or what? i suppose know one will know what im talking about.here are some pics. the one has the hole covered with flesh the other is when i touched it it opened like that. what kind of clam is he/she. he has been in my tank for 1 week. he opens fully and this is the only time i did and ever will touch him. i dont want to stress him.