Claim: A species of sea snail is characterized by its long ribs and a trench which cuts through the ribs.
Evidence: There are many thousands of species of sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs. The gastropods (/ˈɡæstrəpɒdz/), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda /ɡæˈstrɒpədə/. Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine), derived from the notochord. Main articles: Land snail, Freshwater snail, and Sea snail Main article: Slug A snail is, in loose terms, a shelled gastropod. For sea snails, see Sea snail. When the word "snail" is used in this most general sense, it includes not just land snails but also numerous species of sea snails and freshwater snails.