▁the ▁living ▁animals ▁on ych op hor ans ▁( vel vet ▁w orm s ) ▁and ▁tard igr ades ▁may ▁also ▁be ▁members . ▁ ▁In ▁the ▁ 1 9 7 0 s , ▁there ▁was ▁an ▁on going ▁debate ▁about ▁whether ▁multi - cel led ▁animals ▁appeared ▁suddenly ▁during ▁the ▁Early ▁Camb rian , ▁in ▁an ▁event ▁called ▁the ▁Camb rian ▁explos ion , ▁or ▁had ▁ar isen ▁earlier ▁but ▁without ▁leaving ▁foss ils . ▁At ▁first ▁Op ab in ia ▁was ▁regarded ▁as ▁strong ▁evidence ▁for ▁the ▁" expl os ive " ▁hypothesis . ▁Later ▁the ▁discovery ▁of ▁a ▁whole ▁series ▁of ▁similar ▁lo b op od ▁animals , ▁some ▁with ▁closer ▁res embl ances ▁to ▁ar th rop ods , ▁and ▁the ▁development ▁of ▁the ▁idea ▁of ▁stem ▁groups ▁suggested ▁that ▁the ▁Early ▁Camb rian ▁was ▁a ▁time ▁of ▁relatively ▁fast ▁evolution ▁but ▁one ▁that ▁could ▁be ▁understood ▁without ▁assuming ▁any ▁unique ▁evolution ary ▁processes . ▁ ▁History ▁of ▁discovery ▁▁ ▁Charles ▁D ool ittle ▁Wal c ott ▁found ▁in ▁the ▁Burg ess ▁Sh ale ▁nine ▁almost ▁complete ▁foss ils ▁of ▁Op ab in ia ▁reg alis ▁and ▁a ▁few ▁of ▁what ▁he ▁class ified ▁as ▁Op ab in ia ▁media , ▁and ▁published ▁a ▁description ▁of ▁all ▁of ▁these ▁in ▁ 1 9 1 2 . ▁The ▁generic ▁name ▁is ▁derived ▁from ▁Op ab in ▁pass ▁between ▁Mount ▁Hung ab ee ▁and ▁Mount ▁B iddle , ▁sout heast ▁of ▁Lake ▁O ' H ara , ▁British ▁Columbia , ▁Canada