Lithophaga, the date mussels, are a genus of medium-sized marine bivalve molluscs in the family Mytilidae. Some of the earliest fossil Lithophaga shells have been found in Mesozoic rocks from the Alps and from Vancouver Island. The shells of species in this genus are long and narrow with parallel sides. The animals bore into stone or coral rock with the help of pallial gland secretions, hence the systematic name Lithophaga, which means "stone-eater". Their club-shaped borings are given the trace fossil name Gastrochaenolites.