Hmmm....I think the large turbo snails broadcast their eggs and sperm in the water, like Trochus (although I haven't witnessed it - hopefully others can chime in if they've seen theirs broadcast). As I mentioned, Trochus snails broadcast their sperm and eggs and so do stomatella, but Cerith, Nerite, Nassarius will lay eggs on objects in the tank (walls, rock, powerheads, etc.). Hope this helps