As I sit here reading about poly clad flat worms, I think I must have them in my tank. When I changed my lights from MH to LED I had a major clam die off. I always assumed it was the LEDs. I had purchased a new clam about that time and had not QTed it. Over the next few months I lost every large snail in my tank. I assumed the hermits were killing them. I even caught a yellow fancy brittle sea star pulling one of my snails out of his shell. I never thought about flat worms. I had over 100 nassirius snails die. Now I am thinking I have flat worms.