The Checkered Nerite (Nerita tessellata) eats Diatoms, Cyano, Algae and Detritus on the rocks and glass in your tank. Very hardy under normal water conditions. It is called the Checkered Nerite because of the attractive checkered pattern on its shell.  Nerites will consume diatoms, film algae, finer hair algae species, and many species of cyanobacteria - including Lyngbya. These snails are excellent for cleaning the rocks and glass of your aquarium, and are 100% reef safe. They will not consume most display macroalgae, Ulva species are a notable exception though. 
The Checkered Nerite s we ship usually range from about the size of a penny to a nickel in diameter. 
Nerites have a tendency to want to climb out of the water when first added to the aquarium. They should be kept in tanks with lids, or with thick lips on the rim of the tank. This will keep them in and cleaning. Usually after a period of a week they learn their new boundaries pretty well. If they get out before then you can place them back in the tank, they carry water with them in their shell which enables them to breathe if they go above the water line.