▁mic rom oll us ks . ▁ ▁The ▁sub family ▁is ▁sometimes ▁placed ▁in ▁the ▁family ▁C yst isc idae , ▁and ▁is ▁sometimes ▁instead ▁left ▁in ▁the ▁family ▁Mar gin ell idae ▁the ▁margin ▁sn ails . ▁It ▁is ▁within ▁the ▁cla de ▁Ne og ast rop oda . ▁ ▁( Note : ▁Gast rop od ▁tax onomy ▁has ▁been ▁in ▁flux ▁for ▁more ▁than ▁half ▁a ▁century , ▁and ▁this ▁is ▁especially ▁true ▁currently , ▁because ▁of ▁new ▁research ▁in ▁mole cular ▁ph y log eny . ▁Because ▁of ▁all ▁the ▁on going ▁changes , ▁different ▁reliable ▁sources ▁can ▁yield ▁very ▁different ▁class ifications .) ▁ ▁Sh ell ▁description ▁ ▁The ▁shell ▁minute ▁to ▁large , ▁white , ▁uniformly ▁colored , ▁or ▁pattern ed ; ▁sp ire ▁imm ers ed ▁or ▁low ▁to ▁tall ; ▁lip ▁thick ened , ▁smooth ▁or ▁l ir ate ; ▁external ▁var ix ▁present ▁or ▁absent ; ▁si ph onal ▁not ch ▁present ▁or ▁absent ; ▁weak ▁to ▁distinct ▁posterior ▁not ch ▁present ; ▁col um ella ▁multip licate ▁with ▁combined ▁total ▁of ▁ 3 ▁to ▁ 1 3 ▁p lications ▁plus ▁par iet al ▁li ra e ; ▁internal ▁wh or ls ▁c yst isc id ▁type . ▁ ▁Description ▁of ▁soft ▁parts ▁Animal ▁with ▁short ▁to ▁long ▁tent acles , ▁rarely ▁absent ; ▁si phon ▁short ▁to ▁long ; ▁eyes ▁situated ▁later ally ▁on ▁head ▁slightly ▁below ▁the ▁base ▁of ▁the ▁tent acles ; ▁mant le ▁usually ▁not ▁extending ▁over ▁external ▁shell ▁surface .