Originally established as a subclass including the orders Actinodontoida, Unionoida
, and Trigonioida
. Bieler, Carter & Coan (2010) list this taxon as a clade with unspecified rank between superorder and order, and the Bivalve Tree of Life as a superorder. For being more practical and avoiding the multiplication of ranks, we will conserve here the traditional ranking of Pteriomorphia
as subclasses although we acknowledge (as "alternate representation) a clade Autobranchia (=Autolamellibranchiata) including (Pteriomorpha
)). The phylogenetic hypothesis of a clade Palaeoheterodonta
has received overwhelming support from molecular data.