Practice question

Both Brachiopoda and Bivalvia display superficially similar bivalved shells leading to historical confusion yet fundamentally differ in symmetry, orientation and anatomy. Brachiopod valves occupy dorsal and ventral positions, inequivalve, plane bilateral symmetry bisecting each valve medianly, valves not mirror images. Bivalve valves are left and right lateral usually equivalve mirror images with symmetry between valves. Brachiopod shell may be chitinophosphatic or low-magnesium calcite punctate, unlike nacreous aragonite typical bivalves, reflecting independent evolutionary origin of shell secretion from mantle and producing contrasting architecture and hinge mechanisms throughout geological time and fossil record.