The list of marine molluscs of South Africa is a list of saltwater species that form a part of the molluscan fauna of South Africa. This list does not include the land or freshwater molluscs. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (/ˈmɒləsk/). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.