The oldest department in the Natal Museum is devoted to malacology - the study of animals belonging to the phylum Mollusca. Molluscs are soft-bodied creatures such as sea shells, land snails, slugs, squids and octopuses. In terms of the number of species, they are the second largest group of animals in the world, and the largest in the sea. South Africa is estimated to be home to a total of between four and five thousand different species of molluscs.

From the first shells presented in 1879, the department has grown over the years to house the largest collection in Africa, with two research officers and one scientific technician/artist. Although no "official ranking" has been awarded, it has become the de facto "National Collection of Molluscs".