atorial ly ▁along ▁the ▁ske let al ▁cone . ▁These ▁divisions ▁are ▁called ▁strict ures . ▁The ▁strict ures ▁divide ▁the ▁organ ism ▁into ▁segments , ▁typically ▁giving ▁it ▁a ▁more ▁bul b ous ▁shape . ▁Some ▁n ass ell ari ans ▁also ▁exhib it ▁sp ines ▁from ▁the ▁ap ical ▁end ▁or ▁along ▁the ▁later al ▁sides ▁of ▁the ▁cone . ▁Sp ines ▁along ▁the ▁bas al ▁a pert ure ▁of ▁the ▁organ ism ▁are ▁called ▁feet . ▁ ▁E col ogy ▁ ▁Many ▁n ass ell ari ans ▁house ▁din of lag ell ate ▁sym b ion ts ▁within ▁their ▁tests . ▁The ▁n ass ell arian ▁provides ▁am mon ium ▁and ▁carbon ▁dio x ide ▁for ▁the ▁din of lag ell ate , ▁while ▁the ▁din of lag ell ate ▁provides ▁the ▁n ass ell arian ▁with ▁a ▁m uc ous ▁memb rane ▁useful ▁for ▁hunting ▁and ▁protection ▁against ▁harm ful ▁inv aders . ▁There ▁is ▁evidence ▁from ▁small ▁sub unit ▁rib os om al ▁DNA ▁analysis ▁of ▁these ▁din of lag ell ate ▁sym b ion ts ▁that ▁din of lag ell ate ▁sym b ios is ▁with ▁radi ol ari ans ▁evol ved ▁independently ▁of ▁other ▁din of lag ell ate ▁sym b ios es ▁( e . g . ▁for amin if era ). ▁Small ▁sub unit ▁rib os om al ▁DNA ▁analysis ▁also ▁shows ▁evidence ▁that ▁no ▁co e volution ▁of ▁the ▁din of lag ell ates ▁and ▁radi ol ari ans ▁has ▁occurred . ▁