itt ington ▁( 1 9 7 5 ) ▁concluded ▁that ▁Op ab in ia , ▁and ▁other ▁tax a ▁such ▁as ▁Mar rel la ▁and ▁Y oh o ia , ▁cannot ▁be ▁accommod ated ▁in ▁modern ▁groups . ▁This ▁was ▁one ▁of ▁the ▁primary ▁reasons ▁why ▁G ould ▁in ▁his ▁book ▁on ▁the ▁Burg ess ▁Sh ale , ▁Wonder ful ▁Life , ▁considered ▁that ▁Early ▁Camb rian ▁life ▁was ▁much ▁more ▁diverse ▁and ▁" ex perimental " ▁than ▁any ▁later ▁set ▁of ▁animals ▁and ▁that ▁the ▁Camb rian ▁explos ion ▁was ▁a ▁truly ▁dram atic ▁event , ▁possibly ▁driven ▁by ▁unusual ▁evolution ary ▁mechan isms . ▁He ▁regarded ▁Op ab in ia ▁as ▁so ▁important ▁to ▁understanding ▁this ▁phenomen on ▁that ▁he ▁wanted ▁to ▁call ▁his ▁book ▁Hom age ▁to ▁Op ab in ia . ▁ ▁However , ▁other ▁discover ies ▁and ▁anal ys es ▁soon ▁followed , ▁reve aling ▁similar - looking ▁animals ▁such ▁as ▁An om al oc aris ▁from ▁the ▁Burg ess ▁Sh ale ▁and ▁K ery g m ach ela ▁from ▁Si ri us ▁Pass et . ▁Another ▁Burg ess ▁Sh ale ▁animal , ▁A ys he a ia , ▁was ▁considered ▁very ▁similar ▁to ▁modern ▁O nych op hora , ▁which ▁are ▁regarded ▁as ▁close ▁relatives ▁of ▁ar th rop ods . ▁Pale ont olog ists ▁defined ▁a ▁group ▁called ▁lo b op ods ▁to ▁include ▁animals ▁that ▁are ▁thought ▁to ▁be ▁close ▁relatives ▁of ▁ar th rop ods ▁but ▁lack ▁joint ed ▁lim bs . ▁There ▁is