Molluscs

thumb|Cornu aspersum (formerly Helix aspersa)—a common [[land snail]] thumb|Shell of Marisa cornuarietis, a [[freshwater snail]] Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). 86,600 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The number of additional fossil species is estimated between 60,000 and 100,000, and the proportion of undescribed extant species is very high. Many taxa remain poorly studied.