[1] This order dates back to the lower Ordovician period.

They are distinguished from related groups, such as the mussels, by having a straight hinge to the shells, and the adductor muscles being of equal size.

[2] The duplivincular ligament, taxodont dentition, and a shell microstructure consisting of the outer crossed lamellar and inner complex crossed lamellar layers are defining characters of this order.

Moore, 1952,[4] characterised by simple hinge-line dentition consisting of small, numerous, similar hinge teeth, separate mantle lobes, poorly developed siphons, and filibranch gills.

In 2010, Bieler, Carter & Coan[5] proposed a new classification system for the Bivalvia which combines the taxodont Arcida with the dysodont Limida Mytilida, Ostreida and Pteriida as the Pteriomorphia.