Overview of molluscs - Phylum Mollusca

Snails, slugs, clams, mussels, squids and octopuses are all very different-looking animals. However, they are all molluscs.

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.

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