Parasitic snails on my Trochus

[whatcaneyedo]

I just noticed this today. These tiny snails seem to be hiding out in my sandbed and then pouncing on my only Trochus snail whenever it ventures down to the bottom. I've inspected my other snails, an astrea, two turbos, and two abalone and there are no signs of these little buggers on them. They also don't appear to be bothering any of my giant clams (like the derasa in the background). So I've been picking them off and syphoning them out each time I see them. Now here is the punch line: I haven't added anything new to my tank in 7 months and I'm only experiencing this problem now! My last additions were the turbo snails and the elegance coral in early December. However I did have a yellow coris wrasse until recently... it was probably keeping their population down for me.