The Permian nonmarine bivalve Palaeanodonta Amalitzky, 1895: Position in the modern Bivalvia system

Abstract

© 2015, Pleiades Publishing, Ltd. Bivalves assigned to the genus Palaeanodonta Amalitzky, 1895 comprise more than 30 species and are widespread in malacofaunas of the Permian Period in both Eurasia and Gondwana. The history of the establishment of Palaeanodonta, changes in the opinion of the author of the genus concerning its composition and type species are considered. Relationships of Palaeanodonta with the genus Naiadites Dawson, 1860, which was initially regarded as its senior synonym, and with Anthraconaia Trueman et Weir, 1946, which shows superficial similarity, are analyzed. Certain characters, such as the external opisthodetic ligament, reduced pseudotaxodont hinge, crossed lamellar comarginal and radial shell microstructure, resulted in the conclusion that the type species of the genus, Unio castor Eichwald, 1860, the species close to it, i.e., P. longissima (Netschajew) and P. rhomboidea (Netschajew), and also the species included in the group Palaeanodonta fischeri (Amal.) (P. subcastor (Amal.), P. okensis (Amal.), P. parallela (Amal.), P. obunca (Netschajew), P. amalitzkyi (Silantiev)), as well as the group Palaeanodonta dubia (Amal.) (P. umbonata (Amal.), P. sibirzevi (Amal.), P. indeterminata (Amal.), P. monstrum (Amal.)) belong to the genus Palaeomutela Amalitzky, 1892. The species listed are similar in the reduced pseudotaxodont hinge apparatus, which is characterized by a narrow hinge area and few small teeth, which are usually at most ten in number, and occasionally fewer down to complete disappearance. This character is the basis for the recognition of the subgenus Palaeanodonta Amalitzky, 1895 within the genus Palaeomutela Amalitzky, 1892. The diagnoses of the genus, subgenera, and their species composition are provided.