Florida cerith snails, Cerith floridanum, are hardy algae eating snails that fill in the gaps left by some of the other algae eating snails and crabs.  In the wild we see them munching on that purply brown film algae that sometimes grows on the bare substrates.  In our tanks they are real hardy and seem to feed on other green and brown encrusting algae.  They "get along" well with the other snails and don't bother corals or other invertebrates.  They also seem to like to bury in the sand and mud, so they may be great for a refugium.  These snails seem to be extremely hardy and will live for years in just about any aquarium system.