I have the small ones, blue legs. The hermits the local fish store sell come in cerith snail shells, I've got a variety of shells the same size but they insist of cerith shells, so they kill them off, decide the really don't like the shell and im still left with dead snails. I had nassarius snails with my last tank before it crashed, I may try some. what im looking for is something that will pick off detritus and algea off the rocks. the hermits do a great job, but just aren't working out with my snails.