The pen shell, Atrina (Servatrina) lischkeana, stands upside down on the sand where its apex part is buried. After the injection of 2 % Evans blue solution into the sand, the pen shell intermittently discharged Evans blue from the exhalent orifice, inhalent orifice or side slit of the mantle lobes. These results of the experiment revealed that the water in the bottom sediment would be filtered in the mantle cavity by the ventilation of the pen shell.