▁foot ▁could ▁not ▁be ▁m oll us can ▁c ten idia , ▁since ▁these ▁are ▁covered ▁by ▁purely ▁cell ular ▁t issue . ▁Instead ▁he ▁suggested ▁that ▁they ▁might ▁be ▁bra chi op od ▁l oph op hor es , ▁which ▁are ▁feed ing ▁org ans ▁that ▁contain ▁a ▁lot ▁of ▁ext rac ell ular ▁material , ▁or ▁pol ych a ete ▁branch iae , ▁which ▁are ▁resp ir atory ▁org ans ▁composed ▁largely ▁of ▁non - cell ular ▁cut icle ▁– ▁both ▁of ▁these ▁types ▁of ▁structure ▁have ▁been ▁found ▁in ▁the ▁Burg ess ▁Sh ale , ▁in ▁which ▁all ▁the ▁known ▁spec im ens ▁of ▁Od ont og ri ph us ▁have ▁been ▁discovered . ▁ ▁Car on , ▁Sch el tem a , ▁et ▁al . ▁( 2 0 0 6 ) ▁had ▁suggested ▁that ▁the ▁wr ink les ▁on ▁the ▁top ▁surfaces ▁of ▁Od ont og ri ph us ▁spec im ens ▁were ▁caused ▁by ▁the ▁r ipp ling ▁contra ctions ▁of ▁a ▁m oll usc - like ▁mus cular ▁foot . ▁But ter field ▁disput ed ▁this ▁on ▁the ▁grounds ▁that : ▁a ▁m oll us can ▁foot ▁is ▁also ▁mainly ▁composed ▁of ▁cell ular ▁material , ▁which ▁he ▁thought ▁unlikely ▁to ▁be ▁foss il ized ▁in ▁Burg ess ▁Sh ale ▁conditions ; ▁the ▁wr ink les ▁were ▁too ▁straight ▁and ▁ran ▁too ▁precisely ▁across ▁the ▁animals ' ▁bodies ; ▁the ▁g aps ▁between ▁them ▁were ▁the ▁same ▁size ▁as ▁the ▁g aps ▁between ▁the ▁g ill -