What I did for mine was lay a flat rock on the sandbed and stood the clam up and left there for a few days and let it attach itself to the rock. After it was attached I was free to place anywhere on my rock work. HTH
The anemone looks like aiptasia to me, does it retract into the rock if you touch it? If so my opinion would aiptasia.
Not sure about the snail, also in third pic next to the snail is that a red flat worm?