▁on ▁its ▁right ▁side . ▁ ▁The ▁body ▁c ilia ▁are ▁f used ▁to ▁form ▁poly kin et ids ▁called ▁cir ri ▁in ▁some , ▁and ▁are ▁sparse ▁to ▁absent ▁in ▁others . ▁ ▁Form s ▁with ▁cir ri ▁are ▁common ▁throughout ▁soil , ▁fresh water , ▁and ▁marine ▁environments . ▁ ▁Ind ividual s ▁tend ▁to ▁be ▁fl atten ed , ▁with ▁cir ri ▁conf ined ▁to ▁the ▁vent ral ▁surface . ▁ ▁These ▁are ▁various ly ▁used ▁for ▁craw ling ▁over ▁objects , ▁acting ▁as ▁feet , ▁sw imming , ▁or ▁assist ing ▁in ▁food ▁capture . ▁ ▁They ▁are ▁generally ▁divided ▁into ▁hyp ot rich s ▁and ▁st ich ot rich s , ▁but ▁were ▁originally ▁all ▁considered ▁hyp ot rich s . ▁ ▁Form s ▁with ▁sparse ▁or ▁absent ▁body ▁c ilia ▁tend ▁to ▁be ▁smaller ▁and ▁are ▁mostly ▁marine , ▁but ▁a ▁few ▁are ▁common ▁in ▁fresh water . ▁ ▁Again , ▁they ▁are ▁generally ▁divided ▁into ▁o lig ot rich s ▁and ▁ch ore ot rich s , ▁but ▁were ▁originally ▁all ▁considered ▁o lig ot rich s . ▁ ▁The ▁latter ▁group ▁includes ▁the ▁t int inn ids , ▁which ▁produce ▁l or ica e ▁or ▁shell s ▁and ▁are ▁the ▁pre domin ant ▁foss il ▁c ili ates . ▁ ▁As ▁first ▁defined ▁by ▁B üt sch li ▁in ▁ 1 8 8 9 ▁the ▁sp iro tr ich s ▁were ▁one ▁of ▁two ▁orders , ▁together ▁with ▁the ▁now - ab andon ed ▁hol