Trigoniida is order of medium-sized saltwater clams, marine bivalve mollusks. Within the fossil record the occurrence of this order is widespread, ranging from the Devonian Period to Recent. The diagnostic feature for the order is the unique and complex dentition of the shell, (i.e. the interior hinge teeth that articulate the two valves). The dentition is particularly elaborate within the family Trigoniidae. Bieler, Carter, & Coan (2010) included the following families and superfamilies in Trigoniida. Taxa marked with a † are extinct with the only extant family in the order being Trigoniidae.