 Since the year 2000 , taxonomic studies using cladistical analyses of multiple organ systems , shell morphology ( including fossil species ) and modern molecular phylogenetics have resulted in the drawing up of what experts believe is a more accurate phylogeny of the Bivalvia . Based upon these studies , a new proposed classification system for the Bivalvia was published in 2010 by Bieler , Carter & Coan . In 2012 , this new system was adopted by the World Register of Marine Species ( <unk> ) for the classification of the Bivalvia . Some experts still maintain that <unk> should be considered a separate subclass , whereas the new system treats it as the order Anomalodesmata , within the subclass Heterodonta . Molecular phylogenetic work continues , further clarifying which Bivalvia are most closely related and thus refining the classification . 
