 In almost all layers arthropods are the most abundant and diverse group of fossils in the GPB , followed by sponges . 69 @.@ 2 % of GPB individuals and 63 @.@ 9 % of species lived on the surface of the sea bed ; within this group , mobile deposit feeders that extracted food particles from the sediment accounted for 38 @.@ 2 % of the total number of individuals and 16 @.@ 8 % of the total species ; the smallest sub @-@ group was mobile hunters and scavengers ; and the rest were sessile suspension feeders . Animals that lived in the sediment made up 12 @.@ 7 % of the species and 7 @.@ 4 % of the individuals ; the largest sub @-@ group was mobile hunters and scavengers . Bottom @-@ dwelling animals capable of swimming comprised 12 @.@ 7 % of species and 7 @.@ 4 % of individuals . Organisms that spent their whole life swimming were very rare , accounting for only 1 @.@ 5 % of individuals and 8 @.@ 3 % of species . 
