▁mass ▁and ▁a ▁spir al ▁movement ▁of ▁the ▁body , ▁the ▁g ill , ▁the ▁kid ney ▁and ▁the ▁os ph rad ium ▁( which ▁means ▁sens ory ▁re ceptor , ▁or ▁ol factory ▁organ ) ▁have ▁disappeared ▁on ▁the ▁right ▁side . ▁These ▁org ans ▁exist ▁only ▁on ▁the ▁left ▁side ▁of ▁the ▁animal . ▁▁ ▁The ▁heart ▁consists ▁of ▁only ▁one ▁at rium ▁and ▁one ▁vent ric le . ▁ ▁The ▁nerv ous ▁system ▁is ▁also ▁more ▁developed ▁than ▁in ▁the ▁Ar che og ast rop ods . ▁The ▁gang lia ▁are ▁connected ▁with ▁different ▁org ans ▁through ▁n erve ▁path ways . ▁ ▁In ▁the ▁Mes og ast rop oda , ▁the ▁ex cret ory ▁and ▁the ▁re product ive ▁du ct s ▁are ▁separated ▁( in ▁contrast ▁with ▁the ▁most ▁primitive ▁pro sob ranch s ). ▁Many ▁members ▁produce ▁egg ▁caps ules , ▁containing ▁one ▁to ▁more ▁than ▁ 1 , 0 0 0 ▁eggs . ▁ ▁Tax onomy ▁ ▁Here ▁follows ▁the ▁tax onomy ▁of ▁the ▁Mes og ast rop oda ▁( acc ording ▁to ▁the ▁IT IS ) ▁( which ▁is ▁no ▁longer ▁considered ▁valid ). ▁▁ ▁The ▁next ▁tax onomy ▁that ▁was ▁used ▁was ▁ ▁that ▁of ▁to ▁P onder ▁& ▁Lind berg , ▁ 1 9 9 7 . ▁ ▁The ▁current ▁prev ail ing ▁system ▁of ▁tax onomy ▁is ▁that ▁of ▁B ouch et ▁& ▁Roc ro i , ▁ 2 0 0 5 . ▁ ▁Famil ies ▁ ▁Ab ys so ch rys