 Although many non @-@ sessile bivalves use their muscular foot to move around , or to dig , members of the freshwater family Sphaeriidae are exceptional in that these small clams climb about quite nimbly on weeds using their long and flexible foot . The European fingernail clam ( Sphaerium corneum ) , for example , climbs around on water weeds at the edges of lakes and ponds ; this enables the clam to find the best position for filter feeding . 
