Malleidae, or hammer oysters, is a family of saltwater clams. They are related to the pearl oysters, in the order Pteriida and the superfamily Pterioidea. There are about 22 species in this family.

The shells of most of these animals are T-shaped, with the hinge along the top of the T, and with the byssus emerging from the hinge. An oblique ligament holds the hinge. The shell is partially nacreous. There is a single, large adductor muscle. The exhalant current exits at the hinge.

Most hammer oysters live in tropical, coralline areas.

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