Orthida

Orthida is an extinct order of brachiopods which appeared during the Early Cambrian period and became very diverse by the Ordovician, living in shallow-shelf seas. Orthids are the oldest member of the subphylum Rhynchonelliformea (Articulate Brachiopods), and is the order from which all other brachiopods of this group stem.

== Description == Orthids typically possess biconvex, radially ornamented valves that join into a strophic(straight) hinge. The ventral(pedicle) valve is much taller than the dorsal(brachial) valve, which is relatively flat. Because of that, the interarea is also taller on the ventral valve. Radial ornamentation typically occur as costae, which often appear as grooves on the interior surface as well as the exterior. A single median sulcus on the dorsal valve is often present.