</s> ▁Mar gin ell idae , ▁or ▁the ▁margin ▁shell s , ▁are ▁a ▁tax onom ic ▁family ▁of ▁small , ▁often ▁color ful , ▁sea ▁sn ails , ▁marine ▁g ast rop od ▁m oll us cs ▁in ▁the ▁cla de ▁Ne og ast rop oda . ▁ ▁Tax onomy ▁ ▁The ▁higher ▁classification ▁of ▁the ▁family ▁Mar gin ell idae ▁has ▁long ▁been ▁in ▁a ▁state ▁of ▁confusion . ▁Many ▁popular ▁works ▁still ▁treat ▁all ▁members ▁of ▁this ▁family ▁under ▁the ▁single ▁genus ▁Mar gin ella , ▁bas ing ▁them ▁primarily ▁on ▁super f icial ▁similar ities ▁of ▁the ▁shell . ▁ ▁The ▁confusion ▁over ▁the ▁classification ▁st ems ▁from ▁the ▁fact ▁that ▁the ▁earlier ▁class ifications ▁were ▁based ▁rather ▁cr ud ely ▁on ▁shell ▁characters . ▁Although ▁many ▁good ▁differential ▁shell ▁characters ▁do ▁exist ▁within ▁this ▁group , ▁those ▁characters ▁were ▁generally ▁mis inter pre ted ▁or ▁not ▁recognized ▁as ▁significant . ▁Such ▁information ▁as ▁did ▁exist ▁on ▁the ▁rad ula e ▁and ▁the ▁external ▁an atom y ▁of ▁the ▁living ▁animals ▁was ▁widely ▁scattered ▁in ▁the ▁scientific ▁literature , ▁and ▁internal ▁an atom ical ▁descri ptions ▁were ▁not ▁available ▁until ▁fairly ▁recently . ▁ ▁Sh ell ▁description ▁The ▁shell ▁of ▁Mar gin ell idae ▁is ▁usually ▁small , ▁but ▁var ies ▁in ▁different ▁species ▁from ▁minute ▁to ▁medium - s ized . ▁The ▁external ▁color ▁of ▁the ▁shell ▁can ▁be ▁white , ▁cre am , ▁yellow , ▁orange , ▁red , ▁or ▁brown , ▁and ▁can ▁be ▁uniformly ▁colored