Neritina Pulligera, or commonly called Military Helmet, Black Helmet.  
It is widely recommended in aquariums because it is an alga-eater that does not reproduce very easily. It is gasteropode and comes from the Neritidae family. Originally from Indonesia, Thailand, Malaysia and the Philippines.

Feature and behavior:  

Round shell, is like a soldier helmet, the color ranges from brown to black, often shiny. For a 100 lt aquarium it will good the presence of 3 snail, and this will help so much to keep the furniture clean from the algae.  

Feeding and mantenance:  

It is vegetarian, and in the specific alghivora, and, as soon as it is immersed, it will surely make great cleansing of smooth surfaces infested with pointy algae, then it will go to brush algae.  

NOTE : THIS PICTURE IS FOR REFERENCE PURPOUSE ONLY