 Bivalves have been an important source of food for humans at least since Roman times and empty shells found in middens at archaeological sites are evidence of earlier consumption . Oysters , scallops , clams , ark clams , mussels and cockles are the most commonly consumed kinds of bivalve , and are eaten cooked or raw . In 1950 , the year in which the Food and Agriculture Organization ( FAO ) started making such information available , world trade in bivalve molluscs was 1 @,@ 007 @,@ 419 tons . By 2010 , world trade in bivalves had risen to 14 @,@ 616 @,@ 172 tons , up from 10 @,@ 293 @,@ 607 tons a decade earlier . The figures included 5 @,@ 554 @,@ 348 ( 3 @,@ 152 @,@ 826 ) tons of clams , cockles and ark shells , 1 @,@ 901 @,@ 314 ( 1 @,@ 568 @,@ 417 ) tons of mussels , 4 @,@ 592 @,@ 529 ( 3 @,@ 858 @,@ 911 ) tons of oysters and 2 @,@ 567 @,@ 981 ( 1 @,@ 713 @,@ 453 ) tons of scallops . China increased its consumption 400 @-@ fold during the period 1970 to 1997 . 
