Snail
Usually, by 'snail' people mean the snails on land. Land snails usually have lungs, and are in the order Pulmonata. Aquatic snails are in other orders, and usually have gills. Close relatives of the snails are the slugs, which are basically snails without shells. Both slugs and snails are numerous and successful on land. Most land snails and slugs are herbivorous. Aquatic snails and slugs are usually omnivores or predatory carnivores.