foot" for locomotion over the surface. In "欧洲帽贝属" the foot includes the entire ventral surface of the animal. The foot of the双壳纲is a fleshy process adapted by its form to digging rather than to locomotion.头足类的神经系统是除了嵴椎动物以外的有体腔动物当中最复杂的。头足类的外套膜有的巨大神经纤维是神