Enantiomorphous dimorphism in Silurian and Devonian bivalves; Maminka Barrande, 1881 (Lunulacardiidae, Silurian) - the oldest known example

The genus Maminka Barrande, 1881 (Lunulacardiidae) from the Wenlock and Ludlow (Silurian, Lower Paleozoic) of Europe is the oldest known bivalve with enantiomorphous dimorphism which is common among the Silurian and Devonian Lunulacardiidae and Antipleuridae. It represents the result of a special adaptation to the reclining mode of life combined with byssal attachment when early in ontogeny either the left or right valve became the lower valve; later, the bivalve develops as two enantiomorphous sets of shells. Distribution, ontogeny and evolution of this interesting feature in the genera Maminka Barrande, 1881, Stolidotus Hede, 1915, Mila Barrande, 1881, Dualina Barrande, 1881, Antipleura Barrande, 1881, Silurina Barrande, 1881 and Hercynella Kayser, 1878 are discussed.