I noticed that I have a small clam in the top of one of my live rocks and it is living and growing but then I also noticed something under one of my rocks. Last night after the lights went out and everything had retracted I pulled out the flash light and noticed this thing in the cave of the rock. I decided that it is a clam like the other one and it is somewhere from 2 1/2" to 3" long and about 1" tall on the under side of this rock. I never noticed it before and was wondering if it is good or bad? Just leave it and let it grow?
