▁period ▁when ▁this ▁classification ▁was ▁still ▁current , ▁and ▁therefore ▁references ▁to ▁mes og ast rop ods ▁or ▁Mes og ast rop oda ▁are ▁frequently ▁encountered . ▁ ▁The ▁lower ▁tax a ▁that ▁were ▁tradition ally ▁contained ▁in ▁Mes og ast rop oda ▁are ▁now ▁mostly ▁placed ▁in ▁the ▁super order ▁Ca en og ast rop oda . ▁A ▁more ▁detailed ▁account ▁of ▁the ▁tax onomy ▁is ▁given ▁in ▁the ▁articles ▁on ▁Gast rop oda ▁and ▁Arch ae og ast rop oda , ▁and ▁a ▁recent ▁tax onomy ▁is ▁laid ▁out ▁in ▁Tax onomy ▁of ▁the ▁Gast rop oda ▁( B ouch et ▁& ▁Roc ro i , ▁ 2 0 0 5 ) ▁ ▁Description ▁ ▁There ▁are ▁about ▁ 3 0 , 0 0 0 ▁species ▁that ▁were ▁included ▁in ▁this ▁tax on . ▁Most ▁of ▁them ▁are ▁to ▁be ▁found ▁in ▁the ▁sea , ▁but ▁there ▁are ▁also ▁numerous ▁species ▁in ▁fresh water ▁and ▁even ▁a ▁few ▁occur ▁on ▁land . ▁Their ▁shell s ▁have ▁no ▁mother - of - pe ar l ▁or ▁n acre . ▁ ▁Most ▁of ▁these ▁sn ails ▁are ▁her b iv orous , ▁but ▁a ▁few ▁are ▁par as ites ▁or ▁pred ators . ▁The ▁rad ula ▁has ▁seven ▁dent icles ▁( or ▁small ▁teeth ), ▁which ▁are ▁sometimes ▁reduced . ▁ ▁The ▁Mes og ast rop oda ▁are , ▁in ▁many ▁ways , ▁more ▁developed ▁than ▁the ▁Arch ae og ast rop oda . ▁Through ▁t ors ion ▁of ▁the ▁int est inal