formerly:
Class: GASTROPODA   Cuvier, 1797 
Subclass: OPISTHOBRANCHIA Milne-Edwards, 1848 
Order: CEPHALASPIDEA   Fischer, P., 1883
Superfamily: Acteonoidea  d'Orbigny, 1843 

according to Bouchet & Rocroi (2005)
is the superfamily: Acteonoidea no more in the Order Cephalaspidea
now it is with the superfamilies
Architectonicoidea
Glacidorboidea
Mathildoidea
Nerineoidea (fossil)
Omalogyroidea
Pyramidelloidea
Ringiculoidea
Rissoelloidea
Siphonarioidea
in the new informal group Lower Heterobranchia (= Allogastropoda)
have a look at
Bouchet P., Rocroi J.-P., Frýda J., Hausdorf B., Ponder W., Valdés Á. & Warén A. (2005). 
"Classification and nomenclator of gastropod families". 
Malacologia: International Journal of Malacology (Hackenheim, Germany: ConchBooks) 47 (1-2): 1–397.
--
--

-