Interpretative line drawings showing the anatomy of Diandongia (Early Cambrian) indicating the evolution of the mantle canals, disposition of marginal setae, size of visceral area, and the overall shell shape.35The dark blue arrow indicates the inhale currents, and the light blue arrow indicates the exhale currents. Vascula media was lost, and the vascula lateralia on both valves becomes anteriorly sub-parallel in Ordovician and subsequent forms. These modifications likely reflected how water currents circulated within the brachiopod mantle cavity. Because water circulation cannot be definitively recorded from fossils, dashed arrows have been used to represent our interpretation of water circulation in Cambrian and Ordovician linguloid brachiopods. vm, vascula media; vl, vascula lateralia; Dv, dorsal valve; Vv, ventral valve. See also Figure S4.
