▁quite ▁a ▁spect ac ular ▁sight . ▁ ▁N ass ell ari ans ▁feed ▁on ▁other ▁pl ank ton ▁such ▁as ▁small ▁alg ae , ▁b acter ia , ▁di at oms , ▁and ▁small ▁zo op l ank ton . ▁ ▁F oss il ▁History ▁ ▁Early ▁Pale oz o ic ▁radi olar ian ▁foss il ▁history ▁is ▁domin ated ▁by ▁Sp um ell aria ▁until ▁the ▁Car bon ifer ous ▁period , ▁during ▁which ▁n ass ell arian ▁fa una ▁experienced ▁a ▁sharp ▁increase ▁in ▁divers ity . ▁N ass ell arian ▁and ▁sp um ell arian ▁divers ities ▁have ▁been ▁relatively ▁similar ▁since ▁the ▁Mes oz o ic , ▁with ▁dro ps ▁in ▁divers ity ▁after ▁mass ▁ext inction ▁events ▁and ▁a ▁rise ▁in ▁both ▁sp um ell arian ▁and ▁n ass ell arian ▁divers ity ▁during ▁the ▁Qu atern ary . ▁ ▁Sym b ios es ▁between ▁alg ae ▁and ▁radi ol ari ans ▁is ▁observed ▁frequently ▁in ▁ext ant ▁species , ▁but ▁the ▁evolution ▁and ▁timing ▁of ▁this ▁sym b ios is ▁is ▁currently ▁unknown , ▁as ▁the ▁sym bi otic ▁alg ae ▁do ▁not ▁leave ▁behind ▁hard ▁ske let ons ▁to ▁foss il ize . ▁It ▁may ▁be ▁possible ▁to ▁answer ▁this ▁question ▁using ▁is ot op ic ▁analysis , ▁as ▁alg al ▁sym b ion ts ▁prefer entially ▁u pt ake ▁carbon - 1 2 , ▁so ▁sym b ion t - b ear ing ▁cal care ous ▁organ isms ▁such ▁as ▁For amin if era