▁h ollow ▁lo b op od ▁legs ). ▁ ▁L ifest yle ▁▁ ▁The ▁way ▁in ▁which ▁the ▁Burg ess ▁Sh ale ▁animals ▁were ▁buried , ▁by ▁a ▁mud slide ▁or ▁a ▁sed iment - lad en ▁current ▁that ▁acted ▁as ▁a ▁sand st orm , ▁suggests ▁they ▁lived ▁on ▁the ▁surface ▁of ▁the ▁se af loor . ▁Op ab in ia ▁probably ▁used ▁its ▁prob os cis ▁to ▁search ▁the ▁sed iment ▁for ▁food ▁particles ▁and ▁pass ▁them ▁to ▁its ▁mouth . ▁Since ▁there ▁is ▁no ▁sign ▁of ▁anything ▁that ▁might ▁function ▁as ▁j aws , ▁its ▁food ▁was ▁pres umably ▁small ▁and ▁soft . ▁Wh itt ington , ▁bel ieving ▁that ▁Op ab in ia ▁had ▁no ▁legs , ▁thought ▁that ▁it ▁craw led ▁on ▁its ▁lo bes ▁and ▁that ▁it ▁could ▁also ▁have ▁sw um ▁slowly ▁by ▁fla pping ▁the ▁lo bes , ▁especially ▁if ▁it ▁tim ed ▁the ▁movements ▁to ▁create ▁" M ex ican ▁waves ". ▁On ▁the ▁other ▁hand , ▁he ▁thought ▁the ▁body ▁was ▁not ▁flexible ▁enough ▁to ▁allow ▁fish - like ▁und ulations ▁of ▁the ▁whole ▁body . ▁ ▁Classification ▁ ▁Consider ing ▁how ▁pale ont olog ists ' ▁reconst ru ctions ▁of ▁Op ab in ia ▁differ , ▁it ▁is ▁not ▁surprising ▁that ▁the ▁animal ' s ▁classification ▁is ▁still ▁deb ated . ▁Wal c ott , ▁the ▁original ▁descri ber , ▁considered ▁it ▁to ▁be ▁an ▁an ost rac an ▁cr ust ace an , ▁while ▁Le if ▁St ør mer , ▁following