On the early evolution of parallelodontid Arcoidea (Bivalvia)

The Arcida Gray, 1854 are one of eight orders in the bi valve subclass Pteriomorphia (Carter et al. 2011), and an example of outstanding evolutionary adaptation.Originating in the Early Ordovician, the Arcida have a continuous and comprehensive fossil record and occur with a global diversity of approximately 600 species in eleven families today (MolluscaBase 2025).However, the fossil, particularly Palaeozoic Arcida, remain relatively unexplored by taxonomists (Oliver & Holmes 2006).Currently, three or four superfamilies, respectively, are considered valid in the Arcida (Bieler et al.