Group of molluscs
Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly evolved sea slugs and sea snails, (marine gastropod mollusks) within the subclass Heterobranchia. 
Although the great majority of Lower Heterobranchs are indeed marine, a few have succeeded in making the transition to freshwater.
Description.
The shell shapes in this group are typically those that are seen in the sundial, pyramid, rissoella and orbitestellid families of snails.
Taxonomy.
2005 taxonomy.
In the taxonomy of the Gastropoda by Bouchet &amp; Rocroi, 2005, the Lower Heterobranchia is an Informal Group. Superfamilies within the Lower Heterobranchia include:
For a more detailed taxonomy see: Taxonomy of the Gastropoda (Bouchet &amp; Rocroi, 2005)#Informal group "Lower Heterobranchia" (= Allogastropoda)
2010 taxonomy.
Jörger et al. (2010) have redefined major groups within the Heterobranchia: they moved Glacidorboidea and Pyramidelloidea to Panpulmonata.
2014 taxonomy.
Wägele et al. (2014): moved Rissoelloidea and Acteonoidea from Lower Heterobranchia to Euthyneura.
2016 taxonomy.
Kano et al. (2016): moved Ringiculoidea from Lower Heterobranchia to Euthyneura.
So the following taxa remain within the Lower Heterobranchia:
References.
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