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Malacology, the study of molluscs, include chitons, clams, mussels, snails, sea slugs, tusk shells, octopus, and squid. Molluscs live almost everywhere - on the rocky shore, in freshwater habitats and in your garden.

Generally molluscs have:

  • an unsegmented, soft body
  • a muscular foot or tentacles
  • a mantle that can secrete a shell

Most, but not all, molluscs have:

  • an internal or external shell
  • a radula (tongue with teeth)

Molluscs are one of the largest animal groups with about 200,000 species worldwide. The number of species in Australia is about 15,000 with more than 2,000 known from Sydney. Sydney has an amazing diversity of molluscs, from the Little Blue Periwinkle the size of your little fingernail to the Giant Cuttlefish over 1 m long. Despite the many differences in external appearance, their internal structure is very similar. Mollusca means 'soft-bodied' and, although some have developed a tough shell, they are all soft on the inside.

Molluscs are further classified into seven major groups and Sydney has representative from five of these. The main groups found in Sydney are gastropods, bivalves, cephalopods, chitons, and also a minor group, the aplacophorans or spicule worms.

Molluscs can be found in marine, terrestrial and freshwater environments. 99% of Australian freshwater molluscs are endemic to their region, meaning they are found nowhere else on Earth.

Although extremely diverse, molluscs have some common characteristics such as a soft, unsegmented body, a muscular foot or tentacles and a mantle that can secrete a shell. Snails and slugs comprise about 70% of all mollusc species.

Most molluscs with shells produce a highly valuable and shiny object: the pearl. The most desirable pearls are natural pearls, which are formed when a small, foreign object gets stuck inside an oyster.


Mollusc factsheets

63 Fact Sheets in this section