 For the past two centuries no consensus has existed on bivalve phylogeny from the many classifications developed . In earlier taxonomic systems , experts used a single characteristic feature for their classifications , choosing among shell morphology , hinge type or gill type . Conflicting naming schemes proliferated due to these taxonomies based on single organ systems . One of the most widely accepted systems was that put forward by Norman D. Newell in Part N of the Treatise on Invertebrate Paleontology , which employed a classification system based on general shell shape , microstructures and hinge configuration . Because features such as hinge morphology , dentition , mineralogy , shell morphology and shell composition change slowly over time , these characteristics can be used to define major taxonomic groups . 
