Meganodontia acetabulum is described as a new genus and species of the Lucinidae, based on valves trawled at 256~472 m depths on the Tashi fishing ground off the northeastern coast of Taiwan. The new genus is close to Anodontia but differs mainly in the small umbones, the perfectly circular outline, the hinge and ligament, and the large muscle impressions. It is the largest known Recent species of Lucinidae. Other species of bivalves, belonging to families symbiotically associated with chemautotrophic bacteria, have been taken at the same or nearby stations, suggesting that the Tashi fishing ground is a site where chemosymbiosis plays an important role in biomass production and ecosystem function.