Yoldia limatula is a deposit-feeding pelecypod. In Buzzards Bay, Massachusetts, and Long Island Sound it comprises less than 10% (by number) of the total bottom fauna, yet is probably capable of entirely reworking the sediment. Yoldia reworks the sediment by ejecting it several centimeters into the water from its excurrent siphon. Measurements of hourly reworking rates were made under controlled temperature conditions. Extrapolations of yearly reworking rates were determined to be 5-6 l/sq m/yr in Buzzards Bay and 23-51 l/sq m/yr in Long Island Sound. This study suggests that great numbers of organisms may not be required to account for extensive sediment working.