Very large monopectinate ctenidium (1), with elongated filaments hanging from roof of large mantle cavity and their tips (2) resting on the food groove on the floor of the cavity. Strong transverse respiratory current, created by cilia covering the filaments, carries in food material which is trapped as water passes through ctenidium by porous mucus sheets on both its faces. Shell diameter 8mm. Portland Harbour. April 2012.