What kind of shellfish make pearls?

Pearls are produced by molluscs – soft algae or freshwater animals with one (single-leaf) or two (bivalve) shells. Molluscs are invertebrates that do not have a backbone or vertebrae. Scientists estimate that there are over 100,000 different types of molluscs in the world’s waters. However, only a few dozen of these types produce pearls, and only about half of them are used for the production of cultured pearls.

There are two types of shellfish: those that live in salt water and those that live in freshwater. Pearl clams that live in salt water are often referred to as oysters. Pearl molluscs that live in fresh water may be referred to as mussels.