I've had these snails lurking around for about 8 months, since my last major shipment of live rock. I've compared them to pictures of similar looking whelks, which I know prey on snails and clams, but I've observed these for a long time and have never seen them prey on those creatures. Rather, I've seen them much on the rocks and walls as if eating algae. Are they just a special kind of nassarius snail that eats algae? Or are they something I should be worried about?