Umbonal musculature and relationships of the Late Triassic filibranch unionoid bivalves Author Skawina, Aleksandra Author Dzik, Jerzy text Zoological Journal of the Linnean Society 2011 2011-10-25 163 3 863 883 http://dx.doi.org/10.1111/j.1096-3642.2011.00728.x journal article 10.1111/j.1096-3642.2011.00728.x 0024-4082 5441920 ORDER UNIONIDA STOLICZKA, 1871 Emended diagnosis: Freshwater bivalves characterized by linearly arranged pedal elevator attachments in the beak region, but having plesiomorphic nacreous internal shell layer, and, in underived forms, transversely ribbed cardinal teeth of the hinge. Nomenclatorial remark: We prefer Unionida , rather than Unionoida or Unioniformes ( Bogan & Roe, 2008 ), because the ending -ida, not -oida, is generally applied to the genus-derived roots of ordinal-rank names in other molluscan classes and many animal phyla, but the vernacular name ‘unionoids’ is here applied to members of the order to allow a distinction from the family rank taxon Unionidae .