, ▁some ▁are ▁introduced ▁all ▁over ▁the ▁world , ▁syn anth rop es ▁are ▁often ▁severe ▁p ests . ▁ ▁An atom y ▁Most ▁sl ugs ▁in ▁the ▁family ▁Ag ri ol im ac idae ▁are ▁rather ▁small ; ▁only ▁a ▁few ▁( in ▁the ▁gener a ▁Mes ol im ax ▁and ▁K ry nick ill us ) ▁are ▁larger . ▁Most ▁are ▁not ▁more ▁than ▁ 5 0   mm ▁long . ▁The ▁mant le ▁is ▁usually ▁large , ▁occup ying ▁approximately ▁ 1 / 3 ▁of ▁the ▁entire ▁body ▁length , ▁situated ▁in ▁the ▁anterior ▁part ▁of ▁the ▁body . ▁The ▁p neum ost ome ▁is ▁clearly ▁post med ial . ▁The ▁surface ▁of ▁the ▁mant le ▁in ▁living ▁sl ugs ▁is ▁covered ▁in ▁concent ric , ▁mobile ▁wr ink les . ▁In ▁addition ▁sometimes ▁there ▁is ▁a ▁shall ow , ▁poor ly ▁defined ▁gro ove ▁which ▁runs ▁above ▁the ▁p neum ost ome ▁on ▁the ▁right ▁side , ▁not ▁passing ▁to ▁the ▁left . ▁ ▁The ▁pen is ▁is ▁short , ▁usually ▁bag - sh aped , ▁often ▁with ▁external ▁append ages , ▁inside ▁with ▁different ▁stim ul atory ▁org ans . ▁No ▁tub ular ▁memb rane ▁enc ir cles ▁the ▁pen is ▁and ▁vas ▁de fer ens . ▁The ▁pen is ▁ret ractor ▁mus cle ▁is ▁situated ▁beside ▁the ▁right ▁tent acle . ▁ ▁In ▁this ▁family , ▁the ▁number ▁of ▁ha p lo id ▁chrom os om es ▁lies ▁between ▁ 2 6 ▁and ▁ 3 0 ▁(