This is known as a " taxodont dentition " and represents an ancient ancestor.
2.
During the Early Ordovician, a great increase in the diversity of bivalve species occurred, and the dysodont, heterodont, and taxodont dentitions evolved.
3.
In 2010, Bieler, Carter & Coan proposed a new classification system for the Bivalvia which combines the taxodont Arcoida with the dysodont Limnoida Mytiloida, Ostreoida and Pteroida as the Pteriomorphia.
4.
These are deep water clams of a small and primitive order with a taxodont hinge ( composed of many similar, small teeth ), generally with a central ligament pit, large labial palps which are used in deposit feeding and the gills used only for respiration, the anterior and posterior adductor muscles are nearly equal in size, a foot which is divided sagittally and longitudinally with papillate margins.
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