Revision of Late Permian Nonmarine Bivalves of the Genus Opokiella Plotnikov, 1949

Abstract

The genus Opokiella occurs in the Upper Permian (upper part of the Guadalupian–Lopingian) of the East European Platform, sharply differing from members of the Palaeomutela Fauna, which prevails in this territory throughout the Permian Period. Distinctive characters of Opokiella, such as the hinge with a tubercular cardinal tooth and individual pseudotaxodont teeth anterior and posterior to the umbo, thick opisthodent parivincular ligament, and mostly homogeneous shell microstructure, suggest that this group of nonmarine bivalves should be assigned to the monogeneric family Opokiellidae Kanev, 1983 (of the suborder Anthracosiidina Silantiev and Carter, 2011, order Cardiida Férussac, 1822). The genus Opokiella is similar in external characters to nonmarine bivalves known from the Lopingian beds of Tanzania under the conventional name “Carbonicola.”